Conservation ecology of sympatric Asian otters Aonyx cinerea and Lutra perspicillata


Material Information

Conservation ecology of sympatric Asian otters Aonyx cinerea and Lutra perspicillata
Physical Description:
viii, 172 leaves : ill. ; 29 cm.
Foster-Turley, Patricia A., 1952-
Publication Date:


Subjects / Keywords:
Oriental small-clawed otter -- Ecology   ( lcsh )
Smooth otter -- Ecology   ( lcsh )
Oriental small-clawed otter -- Feeding and feeds   ( lcsh )
Smooth otter -- Feeding and feeds   ( lcsh )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )


Thesis (Ph. D.)--University of Florida, 1992.
Includes bibliographical references (leaves 162-171).
Statement of Responsibility:
by Patricia A. Foster-Turley.
General Note:
General Note:

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001759722
notis - AJH2805
oclc - 26736859
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Full Text








This study was accomplished with the help and support

from many organizations, colleagues and friends. All of them

deserve my heart-felt thanks.

Financial or logistical support for this project was

generously donated by a number of organizations. The Marine

World Foundation supported my salary and overhead throughout

six years of this dissertation work. Travel and field work

expenses were covered by an Institute of Museum Services

Conservation Grant. Logistical and staff support in Malaysia

were provided by the Department of Wildlife and National Parks

of Peninsular Malaysia, thanks to the director general,

Mohammed Khan bin Momin Khan. Gas chromatography analyses

were donated by Chevron, USA. The Minnesota Zoological

Gardens and Cheyenne Mountain Zoo provided samples used in

this study. The Florida Museum of Natural History provided

curatorial support. I would like to thank these organizations

and the people involved for this help.

I would especially like to thank Elizabeth Wing, the

chairman of my committee, and Michael B. Demetrios, president

of Marine World, for their personal encouragement and

professional support for this dissertation. I also received

valuable guidance from University of Florida faculty members

Karen Bjorndal, John Eisenberg, Jack Kaufmann, Carmine

Lanciani, Brian McNab, Mel Sunquist, Fred Thompson and Norris

Williams. I am grateful, too, for the input from my fellow

graduate students, especially Mary Bishop, Cheri Jones, Cathy

Langtimm and Jay Malcolm, whose friendships sustained me as we

crossed the hurdles together.

A number of researchers helped with parts of this study.

Burhannudin Mohammed Nor, my Malaysian research counterpart,

provided valuable assistance in the field. Mark Whitten at

the Florida Museum of Natural History provided endless

training and support for the gas chromatography work. Other

help with this portion of the study was provided by Anne

Belcher of Monell Labs and Greg Heminghous of Chevron Research

Labs. Peter Ng of the University of Singapore identified crab

specimens, and Guy Musser of the American Museum of Natural

History identified the mammal remains in my samples. The

staff of the Florida Museum of Natural History, especially

Kurt Auffenberg, George Burgess, Sylvia Scudder and Laurie

Wilkens, were a great help in various aspects of this study.

I also learned much of value from my colleagues and friends in

zooarchaeology, especially Susan de France, Marc Frank, Laura

Kozuch, Lee Newsom and Irvy Quitmyer.

Many members of the international zoo and conservation

community also provided valuable input. I would like to

especially acknowledge the important contributions of Gerry

Binczek, Paul Calle, Ellen Dehrenfeld, Jim Doherty, Susan

Engfer, Jim Estes, Tim Gross, Sheila Macdonald, Chris Mason,


Jay Peterson, Dave Rowe-Rowe, Sompoad Srikosamatara and Duane

Ullrey. Finally, I would like to acknowledge the valuable

personal support I received from my husband, Patrick "Bucko"

Turley, throughout my graduate studies. Without his help and

encouragement, this project would not have been possible.



.age ii
. . .o. ii




Conserving Worldwide Otter Populations .
Asian Otters .......
Conservation Priorities for Asian Otters


Introduction . .
Methods . .
Results . .
Discussion ..............


Introduction . .
Methods . .
Results . .
Discussion . .

. vii

. 4
. 14

. 20
..... 20

..... 25
. 35
. 25
. 35
. 48

S 61

. 61
S 62
S 69
S 82


Introduction . . .
Methods. . . .
Results . . .
Discussion .... . ..


Natural History . . .
Conservation. . . .
Future Work . . .

. 87

. 87
. 93









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of
Doctor of Philosophy



Patricia A. Foster-Turley

May, 1992

Chairperson: Dr. Elizabeth Wing
Major Department: Zoology

Problems in the conservation of two little-known Asian

otter species, the small-clawed otter (Aonvx cinerea

Illiger) and the smooth otter (Lutra perspicillata Geoffroy)

are addressed in this study. Investigations were conducted

to improve otter field survey techniques, to determine the

diet of small-clawed and smooth otters and to gather basic

ecological information on both species.

The volatile components of otter scat were investigated

by gas chromatography for evidence of species, gender and

individual "fingerprints." Chromatograms of samples from

captive small-clawed otters in United States zoos revealed

five peaks that were found in more than 76.7% of the male

samples but were never found in female samples. Different

diets affected the average number of peaks in the


chromatograms but did not overshadow the male peaks.

Chromatograms of ten replicate samples from each of six

control otters were all very consistent, although no

individual "fingerprints" could be found.

In Tanjong Piandang, Malaysia, smooth and small-clawed

otter scats could be discriminated by the presence of

related tracks and by the amount of smearing at the toilet

sites. Scat samples were obtained from known otters of both

species in Asian zoos and from the field. Initial gas

chromatography attempts with these samples were unsuccessful

in identifying species or gender. This was probably due to

deterioration of the samples before the analysis could be


Small-clawed and smooth otter scats were collected from

the Tanjong Piandang study site during four seasons of high

and low water levels. Analysis of prey remains in the scats

indicated year-round dietary and habitat separation between

the two species. Smooth otters ate mostly fish from the

rice field canals, supplemented by rats (Rattus spp.) during

one season. Small-clawed otters ate mostly crabs and

mudskippers (Gobioidei) from the tidal mudflats,

supplemented by small snakes and rice field fish.

Based on these findings, dietary recommendations for

better captive husbandry of small-clawed otters are

suggested. Some ecological and conservation requirements of

both species are also summarized in this study.



Thirteen species of otters belong to the subfamily

Lutrinae of the carnivore family Mustelidae, which also

includes weasels, badgers, ferrets and mink (Corbett and

Hill, 1980). Otters are widely distributed throughout North

America, Central and South America, Europe, Asia and Africa,

and are found in most habitats except for deserts, polar

regions and the highest alpine slopes. Most otters catch

their prey in oceans, rivers, lakes and marshes but spend

considerable amounts of time sleeping, grooming and denning

on dry land. The sea otter (Enhydra lutris), however, is

entirely marine and even gives birth in the ocean.

Otters in North America and Europe have been well-

studied (see reviews in Harris, 1968; Chanin, 1985; Mason

and Macdonald, 1986), but those in other parts of the world

are less well-known (Foster-Turley, 1990a). Of all the

world's otters, those in Asia have so far received the least

attention from biologists and conservationists.

Conserving Worldwide Otter Populations

Threats to Otters

A number of threats to worldwide otter populations have

been identified (Macdonald and Mason, 1990a). In some

places otters are still hunted for their fur, or sometimes,


meat and organs. They sometimes are drowned in fishing nets

or killed by cars. They are often killed by fishermen who

view them as competitors. Direct persecution of otters,

however, is a minor threat to their survival.

The most important threats to the survival of otter

populations are degradations of the clean aquatic ecosystems

that they inhabit. At a high trophic level, otters are

early victims to poisoning of the food chain with pollutants

such as chlorinated hydrocarbon pesticides, heavy metals and

organochlorines such as PCBs (Macdonald and Mason, 1990a).

Any factors that reduce fish populations also have a

deleterious effect on otters. Such factors include

siltation from mining and logging operations, discharges of

organic wastes into rivers and acidification of water

systems from acid rain. Otters also require undisturbed

bank side cover for their survival. Logging along

riverbanks, channelizing rivers through agricultural lands

and "reclaiming" wetlands for agricultural and aquacultural

projects also reduce usable otter habitats.

For a combination of these reasons, five otter species

are listed in the IUCN Red List of Threatened Animals (World

Conservation Monitoring Center, 1990) as Vulnerable. These

species include Lutra felina, Lutra longicaudis, Lutra

provocax and Pteronura brasiliensis of South America and

Lutra lutra in Eurasia. The three Asian species, Lutra

sumatrana, Lutra perspicillata and Aonyx cinerea are listed

as Insufficiently Known.

Conservation Efforts

Increasingly, otters are being used as the symbol for

the survival of healthy aquatic environments, and programs

to conserve otters are gaining momentum (Foster-Turley,

1990a). Surveys to determine where otter populations still

exist and where greater habitat protection measures are

necessary are a first step. Parallel efforts involve

research into such areas as the ecological requirements of

otters, otter reproductive biology and the effects of PCBs

in the food chain. Finally, conferences and education

efforts are needed to disseminate information on otter

biology and to ensure the public's support of otter/wetlands

conservation endeavors.

Such multifaceted otter conservation programs have the

longest history in Great Britain and have spread throughout

Europe. In England and Wales, otter surveys have been

conducted using standardized methods since 1973. These

surveys are performed by trained volunteers and appointed

otter surveyors and are repeated in the same areas every few

years (Mason and Macdonald, 1986). Initial surveys have

been made in most industrialized European nations.

Nationalistic nonprofit otter protection associations now

exist throughout Europe (Macdonald and Mason, 1990b). These

groups lobby governmental agencies on behalf of otter and

wetlands policies and mount volunteer survey efforts in

their countries. Captive breeding cooperative efforts and a

studbook have also been initiated for the European otter.


Otter conservation efforts in the rest of the world lag

far behind those in Europe. This dissertation focuses on

initial efforts towards the understanding and conservation

of otters in Asia.

Asian Otters

Five species of otter occur in Asia. One of these, the

sea otter (Enhydra lutris), is highly specialized for a

marine existence and, in Asia, is found only in the coastal

U.S.S.R. and the Kuril Islands. The biology of this otter

is well-known (see reviews in Kenyon, 1969, 1982; Estes,

1980), and it has been, and continues to be, the focus of

numerous studies and widespread conservation action. The

IUCN Otter Specialist Group recognizes the extent of the

work already accomplished with this species and gives it the

lowest priority for attention (Estes, 1990). This otter

will not be considered in this dissertation.

Asian Small-Clawed Otter (Aonyx cinerea Illiger)

The Asian small-clawed otter is the smallest otter in

the world (Harris, 1968), occasionally reaching weights of 5

kg but generally much smaller. These otters have unique

hand-like front paws with reduced nails which are well-

adapted for catching small vertebrate and invertebrate prey

in shallow, murky water (Foster-Turley and Markowitz, 1982).

This adaptation is also reflected in the expanded tactile

areas of their brain (Radinsky, 1968).


Asian small-clawed otters were historically distributed

from Palawan in the Philippines throughout Southeast Asia,

with a disjunct population in Southern India (Medway, 1969;

Lekagul and McNeely, 1977). In most of their range they are

sympatric with smooth otters (Lutra perspicillata) and often

with hairy-nosed otters (L. sumatrana) or Eurasian otters

(L. lutra) as well. In parts of the Malay peninsula and

Sumatra all four species at one time co-occurred. The

island of Palawan is the only location where small-clawed

otters have not coexisted with another otter species.

In the wild, Asian small-clawed otters have been

observed both singly and in groups (Medway, 1969; Payne et

al., 1985). Groups of four to eight were reported in Padas

Bay, Sabah, Malaysia (Furuyu, 1976). Wayre (1974) saw

small-clawed otter pairs twice on the East Coast of

Malaysia, both times at night. Shariff (1985) reported

signs of these otters at Kuala Pandak Putih, Perak,

Malaysia. Little more is known about the wild behavior and

ecology of this otter.

Asian small-clawed otters are somewhat better known in

captivity. Many small-clawed otters were exported from

Thailand to the United States and the United Kingdom, where

a number of private owners maintained them as pets and wrote

books about their antics (Davis, 1969; Fyson, 1976). In the

mid-1970s the government of Thailand classified them as a

protected species and stopped their exportation by the pet

industry. Due to the difficulties in breeding them

successfully, few of these pets ever reproduced, so few

remain in private hands today. These otters also have a

fairly long history in zoos around the world and by the

early 1970s had successfully reproduced in zoos in the

United Kingdom (Leslie, 1970, 1971; Timmis, 1971) and

Australia (Lancaster, 1975).

All that we know about the social behavior of Asian

small-clawed otters comes from captive studies. In

captivity these animals display a strong pair-bond and both

parents share the duties of rearing their offspring. As

many as seven cubs can be born in a litter following a

gestation period of approximately 60 days. The interbirth

interval can be as short as 10 months, with older siblings

staying with the parents and helping to wean the next litter

(Wilson et al., 1991). Females can begin breeding when only

15 months of age, but only the alpha female in the group


Family groups can easily build up in this way to 15 or

more animals, before the groups become too unwieldy for even

the largest exhibits. To manage the captive population in

United States zoos, same-sexed sibling groups are sometimes

housed together. Introducing new, unrelated animals to

established groups is generally impossible due to the high

levels of aggression displayed. Introducing individual

males to females, however, usually goes smoothly. Based on

the information gleaned from captive management of this

species, it is likely that the social groups observed in the

wild (Furuyu, 1976) are family groups.

Smooth Otter (Lutra perspicillata Geoffrov)

Smooth otters, the largest otters in Asia except for

sea otters, may weigh up to 11.4 kg (Harris, 1968). They

are distinctive in their genus for their flattened tails,

exceptionally large and heavily webbed front paws, smooth

coat and flat upper border of the rhinarium (Roberts, 1977).

Smooth otters are widely distributed throughout

Southeast Asia north to Thailand and west through India and

Pakistan. In most of their range they are sympatric with

the diminutive small-clawed otter, and sometimes also with

L. lutra and/or L. sumatrana. There is also a historical

record of a disjunct population of smooth otters in the

Tigris River Valley, Iraq (Harris, 1968). An otter of this

subspecies (L. perspicillata maxwelli) was immortalized in

the classic book, Ring of Bright Water (Maxwell, 1961).

Smooth otters are reported in small groups that are

thought to be family groups, and they have been seen fishing

cooperatively (Payne et al., 1985). Smooth otters are said

to be jungle foragers, relying on terrestrial prey when

their rivers dry up seasonally. These otters inhabit

marshes, rivers, canals and flooded fields at low elevations

(Lekagul and McNeely, 1977).

Pakistani fishermen along the Indus river historically

used trained smooth otters to chase fish into their nets

(Roberts, 1977). This practice may once have been more

widespread. In Bangladesh today, villagers in the

Sunderbans marshes still raise smooth otters in their homes

and train them to wear harnesses and chase fish (Foster-

Turley, 1990b). Smooth otters are also used in Nepal as

decoys for catching the Gangetic dolphin (Platanista

cangetica) (Shrestha, 1988).

Wayre (1974) saw smooth otters briefly on Penang (a

pair) and Pangkor Islands (a single otter) on the west coast

of Malaysia and watched a party of six smooth otters

catching and eating large silvery fish in the Kerteh River

of the east coast of Malaysia. All his sightings of this

species were during the daytime.

Also in Malaysia, Shariff (1984, 1985) reported smooth

otters in the mangroves of Kuala Gula, the Tembeling River

in Taman Negara, the islands of Langkawi and nearby Anak Gua

Cerita and in Kuala Pandak Putih, Perak. In Taman Negara

smooth otters were most often seen alone, although

occasionally they were seen in pairs or trios. In Kuala

Gula smooth otters were more often seen in groups of five or

more. In all, smooth otters were seen 20 times in Taman

Negara and 19 times at Kuala Gula, always during daytime

hours when they were swimming, foraging or resting on the


Smooth otters are maintained in 12 Indian zoos (Naidu

and Malhotra, 1989) and in a handful of other zoos

throughout Asia. Four litters of smooth otters (Lutra


perspicillata) in the Delhi Zoo were born following

gestation periods of 61 to 62 days (Desai, 1974). The

female alone dug a den and chased away the male and other

females from the vicinity when the cubs were born. The male

rejoined the group when the cubs were weaned at about 130

days and helped feed them fish. Desai (1989) attributed the

opportunity to dig their own dens as a key to their breeding

success. As of October 1988, the Delhi Zoo had 38 smooth

otter cubs born in 13 litters (Naidu and Malhotra, 1989).

These births were year-round, in January, March, July,

October, November and December. Matings, however, were only

observed between August and November, thus suggesting the

possibility of delayed implantation, as was mentioned by

Lekagul and McNeely (1977).

Eurasian Otter (Lutra lutra)

The Eurasian otter is similar to the smooth otter but

can be distinguished by its dense coat with grizzled

guardhairs (Medway, 1969), the "W" shape of the upper margin

of its rhinarium and its thicker tail in cross-section

(Roberts, 1977). The size of adult Eurasian otters in Asia

varies from 4 to 10 kg (Harris, 1968), which is generally

larger than small-clawed otters and smaller than smooth


The Eurasian otter has the largest distribution of any

otter and is found from Ireland east to Japan and from Sri

Lanka and Indonesia north to the Arctic. The Eurasian otter


historically occurred in Southeast Asia south to Sumatra,

with a single specimen recorded in peninsular Malaysia from

the island of Langkawi (Medway, 1969).

This species has been well-studied in the European

portion of its range (see reviews by Harris, 1968; Chanin,

1985; Mason and Macdonald, 1986), but very little is known

about its habits in tropical Asia. Unlike the similar

smooth otter, the Eurasian otter is said to be found in high

altitude habitats. In the Himalayas, Eurasian otters are

reported to travel up to 3500 m altitudes in search of

spawning trout during the summer, but to return in winter to

low altitude pools in the valleys of Kashmir (Roberts,

1977). The Eurasian otter is the only mustelid in Sri

Lanka, where it is distributed in most habitats from coastal

mangroves to mountain streams (DeSilva and Santiapillai,


Hairy-nosed Otter (Lutra sumatrana Gray)

The hairy-nosed otter is very similar to the European

otter morphologically, except for its hair-covered rhinarium

and slightly different skull measurements (Lekagul and

McNeely, 1977). This otter is similar in size to the

Eurasian otter, but has a darker coat with a more distinct

white throat (Harris, 1968).

The hairy-nosed otter has a limited distribution from

southern Laos and Cambodia south to Java. It has been

recorded in the sea off Penang, Malaysia (Medway, 1969).

This otter has not recently been seen in peninsular

Malaysia, although Wayre (1974) speculates that it may still

occur in high altitude streams in the interior. Virtually

nothing is known about the ecology of the hairy-nosed otter.

Current Distribution and Status

Information on the status of Asian otters was compiled
for the First International Asian Otter Symposium in 1988

and published in the IUCN Otter Action Plan (Foster-Turley

and Santiapillai, 1990). This information, based on initial

status surveys or "best guess" estimates by Asian

biologists, conservationists and governmental officials, is

summarized in Table 1.1.

These and other estimates on the status of Asian otters
indicate that the populations are declining (Table 1.1).

The rarest otter species appear to be L. sumatrana and L.

lutra. The hairy-nosed otter historically had the most

limited distribution of any Asian otter. Today it may

already be extinct in peninsular Malaysia and Thailand. The

status of hairy-nosed otters is unknown in Vietnam and

Indonesia, where the last populations may still exist. This

otter is a Species of Global Conservation Concern for the

IUCN Otter Specialist Group (Mason and Macdonald, 1990).

The Eurasian otter is also faring poorly in Asia, although

its wide geographic distribution provides more protection

from species extinction. Smooth and small-clawed otters,

although declining in numbers, are still relatively common

in much of their former range. The Eurasian, smooth and

Table 1.1: The status of otters in Asia, based on the IUCN
Otter Action Plan (Foster-Turley and Santiapillai, 1990).




Hong Kong







Identified Threats
(All otters)

Very rare,declining
Very rare,declining


May be extinct
May be extinct

Very rare,declining


May be extinct

Very rare
May be extinct
Very rare

May be extinct

--land clearing
--fishermen competition
--hunting for fur
--dikes and dams
--pesticides, fertilizers

--logging, siltation
--water pollution
--hunting for fur
--medicinal use of livers

--reduced habitats
--industrial pollution
--medicinal use of livers

--wetlands reclamation
--dikes and dams
--water pollution
--hunting for fur, meat,
aphrodisiac use of bacula

--dikes and dams
--water pollution
--wetlands reclamation
--river gravel extraction

--water pollution
--dikes and dams
--fishermen competition
--hunting for fur

--fishermen competition
--lack of protected areas

--wetlands reclamation
--water pollution
--killing as pests

Table 1.1--continued






South Korea

Sri Lanka




Identified Threats
(All otters)

Very rare,declining
Very rare,declining



May be extinct
May be extinct
May be extinct

Very rare


May be extinct
May be extinct


--water pollution
--hydroelectric schemes
--hunting for fur, meat
--medicinal use of uterus

--hydroelectric schemes
--hunting for fur
--fishermen competition
--reduced habitats

--logging and siltation
--mining contamination
--reduced habitats

--reduced habitats

--reduced habitats

--hydroelectric schemes
--reduction of mangroves

--water pollution
--logging and siltation
--hydroelectric schemes
--reduction of mangroves
--fishermen competition
--lax law enforcement

--reduced habitats

NOTE: The status is given separately for each of the
species, Lutra lutra, Lutra perspicillata (L. persp.), Lutra
sumatrana (L. sumat.) and Aonyx cinerea (A. ciner.). The
threats are common to all the otters in a given country.


small-clawed otters are all listed by the IUCN Otter

Specialist Group as Species of Local Conservation Concern.

The threats to Asian otters are thought to be largely

due to direct human disturbances of their habitats, by

clearing riverine and mangrove forests, reclaiming wetlands,

damming rivers for hydroelectric schemes and polluting

waterways with agricultural and industrial wastes. Otters

are often killed where they are thought to compete with

fishermen, and they are sometimes hunted for fur, meat or

various organs for supposed medicinal or aphrodisiac


Conservation Priorities for Asian Otters

All otters worldwide have a similar set of conservation

priorities (Mason and Macdonald, 1990). These priorities

include trying to reduce the threats of water pollution,

habitat destruction, overhunting, and conflicts with

fishermen. In addition, more research into otter biology

and more public education programs are needed. In cases of

severely threatened populations, captive breeding and

possible reintroductions may also be useful.

The Asian otter species are particularly problematic

due to the lack of basic ecological information on these

species. Accordingly, the IUCN Otter Specialist Group lists

two initial priorities for smooth, small-clawed and hairy-

nosed otters (Mason and Macdonald, 1990): to conduct field

surveys to determine current distribution and status and to

study the ecology and conservation requirements of these

species. Other conservation priorities for Asian otters


include better legislation and protection of otters and

their habitats and potential captive breeding and

reintroduction programs.

In this dissertation, my aim is to contribute to the

conservation of Asian otters by addressing some of the

priorities developed for these species. My work focuses on

problems in three areas: captive husbandry, survey

techniques and compilation of basic ecological information

on these species.

Captive Husbandry and Breeding

Initial Asian otter conservation efforts began with the

study of Asian small-clawed otters in captivity. In 1981,

this species was designated one of the first Species

Survival Plan (SSP) species for the American Association of

Zoological Parks and Aquariums (AAZPA) (Foster-Turley and

Engfer, 1988). A captive Master Plan for this species was

formulated in 1988 (Engfer and Foster-Turley, in press) and

is updated yearly by the AAZPA Asian small-clawed otter SSP

Committee. Asian small-clawed otters are now maintained in

18 institutions in North America and are breeding in five of


The first regional studbook for Asian small-clawed

otters was begun in 1985 (Foster-Turley, 1985) and has been

periodically updated by the succeeding studbook keeper

(Engfer, 1991). Another regional studbook for Asian small-

clawed otters in Australasian zoos has been initiated by

Chris Banks, Melbourne Zoo, Australia and a similar regional

studbook for Europe is being coordinated by the London Zoo.


All the regional data on captive Asian small-clawed otters

will soon be incorporated into an International Studbook,

with Susan Engfer as studbook keeper.

Despite this international attention, two impediments

to the successful captive husbandry and breeding of Asian

small-clawed otters still exist. The first issue is a

health problem. Two-thirds of the captive population suffer

from urinary calculi (kidney stones), the most often cited

cause of their death (Calle, 1988). A detailed analysis of

the studbook reveals no genetic trends, and this affliction

is thought to be nutritional in origin, related to an

improper captive diet. However, there has been no

information on the wild diet of this otter, which I have

attempted to remedy as one component of this dissertation

(see Chapter Four).

The second problem is a reproductive one. Population

managers still cannot encourage genetically chosen pairs to

reproduce, despite extensive habitat improvements and re-

pairings. Some pairs do reproduce, and then, often, too

prolifically, with up to two litters of seven offspring per

year. Other pairs, although behaviorally compatible, never

reproduce. The lack of solid reproductive information on

both sexes has been pinpointed as a major problem for these

otters. A detailed reproductive study at the Minnesota Zoo

aims to address this problem, as well as provide a control

group of animals for the gas chromatography work described

in Chapter Two.

Survey Techniques

British conservationists were the first to develop

methods to survey otters (Mason and Macdonald, 1986). The

secretive behavior of European otters, like most otters,

makes it very difficult to assess their numbers by direct

counts of the animals. The British otter survey method

relies on noting the presence of otter tracks and scats

(called sprintn" in Europe) along measured stretches of

rivers and streams.

Although scat surveys have been used to make population

estimates for other species (Putnam, 1984), there is

controversy about the use of this method for making

population estimates for otters (Mason and Macdonald, 1987;

Kruuk and Conroy, 1987). One problem with this technique is

the differential scent-marking behavior of otters during

various seasons and the resulting lack of correlation

between numbers of scats and numbers of otters in the

population. Researchers in Scotland (Jenkins and Burrows,

1980) and Louisiana (Shirley et al., 1988) have tried to

estimate otter populations by injecting captured otters with

radioactive zinc and using standard mark and recapture

formulas based on the detection rate for radioactive


In Asia, initial otter surveys are even more difficult

than in much of the developed world. Most of the remaining

otter habitat is uncrossed by roads and bridges, which in

Europe provide easy access to the streams and rivers. It is

unlikely that the radioactive zinc technique will have wide


utility in Asia due to the logistics and permits involved. In

Asia, otter surveys are also complicated by the fact that two,

three, or even four species of otters are sometimes sympatric

and differentiating their signs could be difficult.

One technique that has been attempted to differentiate

the scats of sympatric carnivores is the use of thin layer

chromatography of fecal bile acids (Major et al., 1980).

Johnson et al. (1984) compared this technique with visual

determinations of field signs to discriminate the scats of

bobcats and mountain lions and found that field signs were

more accurate. They also performed initial experiments

using gas chromatography and suggested that this might be a

more reliable technique. Gas chromatography of pure scent

extractions from the glands of various carnivore species

have yielded information on species, gender and individual

identity (see review in Gorman and Trowbridge, 1989).

Initial gas chromatography work with European otter scats is

intriguing but inconclusive (Trowbridge, 1983).

If species, gender and individual identity can be

determined from gas chromatography assessment of otter

scats, this technique will have wide utility in surveys of

otter populations throughout Asia and elsewhere and with

other species as well. Experimental work with this

potential scat surveying technique is the second focus of

this dissertation (Chapters Two and Three).

Ecological Studies of Asian Otters

The third focus of this study is to gather initial

information on the ecological and conservation requirements


of Asian otters in the wild (Chapters Three and Four).

During pilot studies in Malaysia (1984) and Thailand (1987)

four potential study sites were located (see Appendix A).

One of these, a rice field and mangrove habitat near Tanjong

Piandang on the northwest coast of Malaysia, was chosen for

a number of reasons. This site contains sympatric

populations of smooth and small-clawed otters that are

easily accessible by jeep and boat. It is also near Penang

and Langkawi Islands, where the last hairy-nosed and

Eurasian otters in peninsular Malaysia were reported

(Medway, 1969), thus presenting the possibility of sightings

or information on these rare animals.

The Malaysian government offered generous support for

this project in the form of necessary permits, vehicles,

boats and personnel and a five-year commitment of time and

expenses for a counterpart researcher, Mr. Burhannudin

"Bond" Mohammed Nor. Two Royal Forestry Department

biologists from Thailand, Ms. Budsabong Kanchanasaka and Ms.

Kalyanee Boonkird, also worked with us to learn techniques

for a parallel otter study in their own country. The

involvement of Thai and Malaysian biologists will ensure

that the work begun in this field study continues toward a

greater understanding of the ecology of these otters.

In conclusion, it is hoped that this dissertation will

provide useful information for the conservation of two Asian

otter species. It is also hoped that the techniques

developed will find wider applicability towards the

understanding and conservation of all of the world's otters.



Otters have a well-developed sense of smell and seem to

order their world around their communication and perception

of scent. Captive otters spend much of their time carefully

depositing their scat in particular locations and in

olfactory investigations of other otter's scats in their

enclosures. Since the smell of their scat appears to serve

a communication function for otters, any interpretations of

these scent messages could produce a window of understanding

on their behavior in captivity and their ecology in the

field. Before the complexities of field work can be

attempted, it is necessary to study the scent of otter scat

under the controlled conditions of captivity. That is the

focus of this chapter.

Mammalian Olfactory Communication

Many mammals communicate with conspecifics through

emitting and detecting olfactory signals. Much of this

evidence is summarized in early review papers (Ralls, 1971;

Eisenberg and Kleiman, 1972; Johnson, 1973; ). A recent

review paper (Gorman and Trowbridge, 1989) summarizes

advances in the study of mammalian scent since these earlier



Odor chemists have identified certain components of the

scent marks of mammals including dogs (Schultz et al.,

1985); foxes (Albone et al., 1974; Albone and Perry, 1976);

wolves (Raymer et al., 1986a, 1986b); skunks (Anderson and

Bernstein, 1975); mink (Brinck, 1978; Sokolov et al., 1980);

ferrets (Crump, 1980); tamarins (Epple et al., 1979, 1988;

Belcher et al., 1988); rabbits (Mykytowycz, 1979); voles

(Welsh et al., 1988); guinea pigs (Wellington et al., 1983)

and deer (Muller-Schwarze and Muller-Schwarze, 1975).

Certain volatile components of the anal glands (Gorman et

al., 1978; Brinck et al., 1983) and urine (Trowbridge, 1983)

of European otters (Lutra lutra) have also been


Ascribing a biological function to identified mammalian

odors is difficult (Stoddart, 1976; Preti et al., 1977;

Ritter, 1979; Mykytowycz, 1979). The standard bioassay

techniques used with insects rarely apply to the

complexities of mammalian behavior. Nevertheless,

researchers using captive mammals have demonstrated that

some scent messages contain information on species (Brinck

et al., 1983; Belcher et al., 1988; Epple et al., 1988;

Welsh et al., 1988; Apps et al., 1990), subspecies (Muller-

Schwarze and Muller-Schwarze, 1975; Epple et al., 1979),

sexual condition (Epple, 1978; Bailey et al., 1980; Gorman,

1980; Henry, 1980; Macdonald, 1980; Raymer et al., 1986b;

Jemiolo et al., 1987) and individual identity (Rasa, 1973;

Gorman, 1976; Stoddart, 1976; Brinck, 1978; Yamayaki et al.,



Although it is much more difficult to locate the scent

marks of mammals in the field (Macdonald, 1980), biologists

studying foxes (Henry, 1980) and wolves (Mech and Peters,

1977) have succeeded in collecting and analyzing urine scent

marks from free-ranging animals. Researchers predict that

the odors of scent marks in the field may vary with the diet

(Classon and Silverstein, 1977), but this has not been


Otters as a Model for Scent Studies

Carnivores (Order Carnivora) are well-endowed with

scent glands and demonstrate a wide range of marking

behaviors (Ewer, 1973; Rasa, 1973; Mech and Peters, 1977;

Henry, 1980; Macdonald, 1980). Most carnivores, including

all otters except for sea otters (Enhydra lutris), possess

both proctodeal and anal glands (Stubbe, 1969, 1970; Gorman

et al., 1978). Otters do not exhibit the anal marking

behavior more typical of other mustelids with more

specialized anal glands (Stubbe, 1970). Instead, their

marks are deposited along with their scats in conspicuous

locations that are often used repeatedly. The build-up of

waste products in these areas often affects the growth of

vegetation, making these toilet sites conspicuous to the

field researcher. Otters often urinate and defecate

simultaneously (personal observation) so any volatile

components in their urine are also deposited with the feces.

For these reasons, otters are particularly good subjects for

the investigation of their scent marks in the wild.

To the human nose, European otter scat has a

distinctive sweet scent. Otter surveyors in Europe depend

upon this scent to identify otter scat from mink, cat, dog

or other similar scat when no tracks are evident. *Several

techniques have been used to study the scent produced by

otters. Gorman et al. (1978) investigated the anal scent

sacs of the European otter through histological and chemical

analysis. Using gradient gel electrophoresis, they found

that individual differences in the protein components of the

anal gland secretions from two otters were constant over a

three-month time period. Brinck et al. (1983) found

taxonomic similarities as well as species-specific

differences in the chemical composition of the anal sac

secretions of seven mustelid species, including European


In the field, it has been proven that the scats of

European otters are not randomly distributed in the

environment, but instead occur at prominent, conspicuous

locations (Trowbridge, 1983). This well-accepted fact has

long been the basis for otter surveys throughout Europe

(Mason and Macdonald, 1986) and has led to widespread

speculation that the otters themselves use the scent

deposited in these scats to identify other individuals. A

small study by Mason and Macdonald (1986) demonstrated that

when scats of captive otters were placed beside wild otter

scats, these toilet areas were marked with more scats than

control toilet areas with no unknown scats added. This

seems to indicate that wild otters recognize an unfamiliar


animal's scats and respond to this stimulus by remarking

their toilet sites.

Trowbridge (1983), using a double-blind presentation of

samples in discrimination tests, found that a trained

captive male European otter could discriminate the scent of

known and unknown otters. Trowbridge also used gas

chromatography techniques to record the scent profile of ten

scat samples from each of three otters over a 25 day period,

in a search for individual differences. Using an ether

extraction technique and a temperature program from 900 to

2900C at 50C/minute, she located the same 98 peaks in all of

these scat samples. There was substantial variation in the

peak proportions within samples from one animal and between

individuals, but no single peak varied significantly among

the three individuals. When any two individuals were

compared, from 9 to 33 peaks varied in their proportions

depending on which pairs of individuals were examined.

These results suggested individual differences in the scent

components of individual European otters, although the

chemical components were not identified.

Since the Trowbridge study, the tools and techniques of

gas chromatography have been substantially refined. In this

chapter, modern gas chromatography techniques are used to

analyze the volatile components in the scat of captive Asian

small-clawed otters (Aonvx cinerea). First, individual and

gender-related scent "fingerprints" are investigated in the

chromatograms from individual otters. Then, the effects of

different diets on the scent of a group of otters are

examined. The captive work in this chapter provides the


foundation for the field application described in Chapter




Asian small-clawed otters are highly social and are

seldom maintained alone in zoo enclosures. When one

individual in a group defecates, the others rush over to add

their contribution to the community toilet site. It is

stressful for a group of these otters to be separated even

for the short periods of time necessary to obtain pure

individual scat samples.

Fortunately, during the course of this dissertation

project the Minnesota Zoological Park, Apple Valley,

Minnesota, was conducting a tightly controlled reproductive

study. Six Asian small-clawed otters (three males and three

females) were housed separately in identical concrete-

floored cages. The otters could hear and smell each other

but could not see or touch their neighbors. After the

initial stress of separation, the otters became calmer and

apparently adapted to their solitary routine.

Each female otter was anaesthetized weekly for the

reproductive study; the males were also anaesthetized twice

during the scat collection period. Various combinations of

anaesthetics were used, including Telazol, isofluorine gas,

a mixture of ketamine hydrochloride and tranquilizer Versid,

and a mixture of ketamine hydrochloride and tranquilizer


Valium. To minimize any effect these drugs or the stress of

capture might have had on the scent produced by the otters,

all samples were collected on the morning previous to any

experimental procedure and at least a week following any

past immobilizations. The scat samples were taken from the

cages of each of these six otters once a week for a total of

ten weeks, from August to October 1989. These samples were

used to test for individual and gender-related differences.

Five female siblings were housed as a group at Marine

World, in Vallejo, California. Attempts to collect

individual scat samples resulted in the otters screaming and

clawing at the doors which separated them. Under these

conditions a "normal" defecation seemed impossible, and this

procedure was discontinued. Scats from the community pile

of this group were collected in August, 1990. These were

tested for gender-related characteristics and used for

dietary trials.

In four instances, keepers were able to obtain a known

individual scat sample from one of the Marine World females

before the rest of the group contaminated it. Four weekly

scat samples were also obtained in May/June 1990 from a

temporarily solitary male otter at the Cheyenne Mountain

Zoo, Colorado Springs, Colorado. These samples were also

tested for gender-related differences.

In summary, individual samples were obtained from the

otters listed below. Ages are given at the time of scat



1. MF35: female, 9 years old, Minnesota (10 samples)

2. MF37: female, 3 years old, Minnesota (10 samples)

3. MF82:, female, 4 years old, Minnesota (10 samples)

4. MM02: male, 2 years old, Minnesota (10 samples)

5. MM38: male, 2 years old, Minnesota (10 samples)

6. MM34: male, 1 1/2 years old, Minnesota (10 samples)

7. Toby: male, 12 years old, Cheyenne Mt. (4 samples)

8. VFB: female, 1 year old, Marine World (1 sample)

9. VFO: female, 1 year old, Marine World (2 samples)

10. VFX: female, 1 year old, Marine World (1 sample)

Although individual samples were not obtained from

these otters, they were included in the group scat


11. VFR: female, 1 year old, Marine World

12. VFN: female, 2 years old, an older full sibling of

the other Marine World females

Captive Diets

Otters are active animals that require relatively large

amounts of food, up to 10% of their body mass each day

(Harris, 1968). The Bronx Zoo nutrition staff has calculated

that a single 4 kg Asian small-clawed otter requires 2299

kilojoules of food each day (Wilson et al., 1991). All of

the otters in this study received more than this minimum

food requirement, divided into two meals per day.

All individual scats were collected from otters

maintained on their standard zoo diet. At both the

Minnesota Zoo and Cheyenne Mountain Zoo the otters were fed

a commercial horsemeat based mixture (Nebraska brand),

grated carrots and occasional fish. At Cheyenne Mountain

Zoo, male otter Toby was also fed chopped kale and

supplemental Vionate multiple vitamins. The Marine World

otters were fed a mixture of canned feline ZuPreem brand

diet, lams brand cat kibble and chopped assorted sea fish

species supplemented with Vionate multiple vitamins.

For the feeding trials, the Marine World otters were

fed experimental diets that were intended to replicate as

closely as possible the diets ingested in the wild. As it

was impossible to feed the otters native Malaysian fauna,

available fauna of related taxa were substituted. Each diet

was fed exclusively to the animals for 24 hours prior to

scat collection, except as noted below. In most cases, the

otters readily consumed the novel diets, fed either dead or

alive. Scat samples containing remnants of these prey items

were collected from the community pile on the morning

following the last feed of each item. The experimental diet

trials included:

Trial 1: Grass shrimp (Crangon franciscorum). This

small crustacean less than 2.5 cm in length was

obtained from a San Francisco Bay bait store and fed

live and frozen/thawed. (5 samples)

Trial 2: Crayfish (Pacifastacus leniusculus). This

larger crustacean up to 20 cm long was obtained from a

San Francisco Delta wholesaler and fed live. (8



Trial 3: Fish. Pelagic smelt (Osmerus mordax) and

herring (Clupea harenaus) were obtained frozen from a

fish wholesaler and combined portions of equal amounts

of both species were fed thawed. (5 samples)

Trial 4: Insects. Crickets (Family Gryllidae) were

obtained from a pet store and fed to the otters both

live and frozen/thawed. Because not enough crickets

were available to provide 100% of the otters' diet for

24 hours, this was supplemented with the standard

feline ZuPreem diet. (5 samples)

Trial 5: Adult water snakes. Snakes (Nerodia spp.)

were obtained from a California reptile dealer who

imported them from Florida. When live adult snakes

were presented, the otters displayed curiosity, but

showed no inclination to capture and consume this prey.

When dead chopped snakes were first presented, all of

the otters also rejected this novel food item.

Finally, chopped snake was gradually added to the

standard Zupreem diet over a period of three days,

until finally an evening meal of mostly snake was

ingested by some of the animals, while others refused

to eat it. "Snake" scat samples were taken the

following morning from portions of the community pile

that contained excreted snake skin. (5 samples)

Trial Six: Baby Snakes. Following a serendipitous

live-birth of water snakes in the holding barrel, baby

snakes were offered to the otters. These were readily


captured and consumed as a supplement to the standard

canned feline Zupreem diet. (2 samples)

Trial Seven: Zoo Diet. The standard Marine World

otter diet of canned feline Zupreem and dry lams brand

cat kibble without the addition of fish was fed to the

otters. (5 samples)

Scat Collection. Preservation and Handling

Preliminary gas chromatography work was conducted with

North American (Lutra canadensis) and Asian small-clawed

otter scat at the Florida Museum of Natural History and at

Monell Labs in Philadelphia. The gas chromatography

protocol used in this study was formulated with the help of

Dr. Mark Whitten at the Florida Museum of Natural History.

All scat samples were transferred from each otter's

cage floor to sterile glass bottles with teflon lids using

sterile disposable pipettes. All bottles and pipettes used

to collect all scats at all three facilities were identical.

All scat samples were immediately placed in a standard

freezer. When all samples had been collected at the

Minnesota Zoological Gardens and Cheyenne Mountain Zoo, they

were mailed with dry ice to my laboratory at Marine World in

Vallejo, California. Those samples collected directly at

Marine World were also immediately placed in a standard

freezer for later processing.

At Marine World, all scat samples were thawed and

weighed and an equal amount by weight of nanograde methylene


chloride was added to each bottle. The contents of the

bottles were thoroughly mixed, and allowed to stand for 24

hours at room temperature. Sterile disposable pipettes were

used to transfer small amounts of the clear liquid above the

sediment to amber gas chromatography vials. These vials

were transported immediately to the Chevron Research

Laboratory in nearby Richmond, California. At Chevron, the

extracted samples were again placed in a standard freezer

for periods of time up to a month before they were analyzed.

Gas Chromatographic Analysis

At the Chevron labs, all extracted samples were thawed,

and then filtered, if necessary. They were analyzed with a

Hewlett Packard 5790 gas chromatograph using a 25 m HP-1

column 0.2mm in diameter and a 0.5 micron film. The

injection port temperature was maintained at 2500C under 20

psig of helium. A splitless injection of 1 microliter of

each sample was injected using an autosampler. The

temperature of the gas chromatograph was programmed from

500C with a 1 min. hold to 3000C with a 5 min hold at a rate

of 60/min.

Data Analysis

Gas chromatography data are presented in graph form

with associated lists of numbers pinpointing the time during

the programmed temperature regime when each volatile

compound in the sample eluted (the "retention time") and how


much of this compound was present (the area under each

peak). The amount of each compound present in the sample

depends on the size of the sample, so a calculated "area

percent" (the area under each peak divided by the total area

under all peaks in a sample) is usually the basis of

analysis of these data. Because the large methylene

chloride solvent peak eluted during the first minute of the

runs, the area percent were calculated on all peaks

beginning after the first minute.

Retention time alone cannot identify the chemical

composition of any compound without further expensive mass

spectrometer analysis and comparison with a reference

library of compounds. Many compounds in mammal scent have

not yet been identified, and this process often involves

years of work by specialized chemists. For the purposes of

this study, no attempt was made to identify any of the

compounds present. Instead, the data were analyzed for

scent "fingerprints" that show particular peaks and peak

areas for different subjects and experimental conditions.

The largest peaks do not necessarily represent those

compounds with the strongest "smell." The "smell" of a

substance is a function of the olfactory receptors of the

animal in question as well as the total amount and nature of

the volatile compound that is present. Even the smallest

peaks might be essential to the otter's perception and

interpretation of a scent. For this study, methods were


developed to compare all the peaks in the chromatograms, not

just the largest ones.

One problem with gas chromatographic analyses of many

samples with a large number of peaks is identifying the same

peak in different samples. Even when the temperature

program is held constant, and the same chromatograph is used

for repeated runs, the same compound may elute at a slightly

shifted retention time, due to slight uncontrollable

differences between the runs. In retrospect, the addition

of a known standard into the samples and the calculation of

the relative retention times of various peaks based on this

known standard would help alleviate this problem with data

analysis. Alternately, if a strong peak always appeared in

a similar location in each sample this could reasonably have

been accepted as the same compound and relative retention

times could have been calculated using this standard peak.

Unfortunately, no standard peak appeared in all samples and

no known standard was added, so other ways of naming and

numbering common peaks were developed.

When the data set was sorted by retention time into one

list of 3805 records and the sample numbers and retention

times for various segments were examined, certain patterns

appeared. In a few sections of the chromatograms, the

entire series of 60 samples from Minnesota Zoo animals

appeared in reverse order to the order in which they were

run. This gave strong evidence to the fact that these areas

actually represented a single compound that eluted slightly


earlier in successive samples that were run together. The

width of this range of retention times for a single compound

depended on its position in the series and also on the

amount of area under the peaks. Although it was not obvious

in all cases where the series began and ended for each

compound, it was found that in most series a gap of at least

0.05 marked the borders of a single peak. A set of

empirical rules were thus evolved to guide in identifying

common peaks.

1. When all results are ordered in a series by

retention time, if the retention times follow a gradual

series any gap in the series of more than 0.05 marks

the beginning of a new peak.

2. If the above rule includes the same sample

number twice, then this is evidence that more than

one actual compound exists within this series. In

this case the series is next split into two peaks

at the biggest gap within the series.

3. If there is a long series with duplicate

samples but with no obvious gaps to apply rule

number 2, then the peak is split into two where

the duplicates start.

Two types of errors can result with these numbering

rules. One type of error is to include a few separate

compounds under a single peak classification. Initially,

44 peaks out of the 273 total peaks numbered by Rule 1 had

to be relabelled due to duplicates within this system (Rules


2 and 3). In these cases, the gap criterion of 0.05 was too

high and more than one compound was initially included in

the same peak. The other type of error is one in which the

same compound is split and given two or more different peak

numbers. This would happen if the arbitrary gap criterion

of 0.05 is too low. There is, however, no evidence within

these data to show that peaks were split.

The gap range criterion of 0.05 was chosen as a

conservative numbering system, which may have merged

separate compounds of individual importance but was unlikely

to have split them into two peak identifications. If

individual differences in the scent profiles are due to

unique compounds possessed by only certain individuals, then

this conservative lumping technique could have obscured this

finding (a Type II error) but it is unlikely that it led to

Type I errors. The data were found to be robust enough to

accommodate these potential errors and to still yield

significant results.


Description of Chromatograms

Visual inspection of all 103 chromatograms obtained for

this study reveals two general patterns. The 60

chromatograms from the Minnesota Zoo and the 4 individual

Marine World chromatograms display the first pattern, with

peaks evident throughout the full range of retention times

(Fig. 2.1 and Fig. 2.2). By contrast, the 35 group Marine


World samples and the 4 Toby samples display the second

pattern, with most of their activity only at later retention

times (Fig. 2.3). Many of the chromatograms of both types

share common large peaks around 9.5, 34.6 and 37.4 minutes.

Of all the samples, the most consistent in appearance

are the 60 samples obtained from the six Minnesota Zoo

otters (Fig. 2.1 and Fig. 2.2). Most of these chromatograms

display single large peaks at retention times around 1.1,

1.9, 7.1, 9.5, 29.1, 34.6 and 37.3 minutes and a series of

large peaks between 22 and 27 minutes. Each sample has from

35 to 79 peaks, with an overall average of 55 peaks per


The individual Marine World female samples, like those

from Minnesota animals, also have peaks throughout the full

45 minutes of the runs, with large early peaks around 2.8

and 9.5 minutes. These chromatograms also have many peaks

between 3 and 4 minutes, between 15 and 19 minutes, around

22 minutes, from 25 to 27 minutes and at 29 minutes. These

samples have from 31 to 37 peaks each, with an average of 34

peaks per sample.

The second overall pattern is evident in the 35 group

feeding trial samples (Fig. 2.3) and the 4 samples from male

Toby (Fig. 2.4). Although a few of these chromatograms have

peaks in the vicinity of 2.8 minutes and 9.5 minutes, the

rest of the activity is only evident at later retention

times. The Toby chromatograms have little activity before



0 5 10 15 20 25 30 35 40 45
Time (min)

Figure 2.1: Chromatogram from the scat of a representative
male Minnesota Zoo otter showing a typical pattern of peaks
for males in this series.

0 5 10 15 20 25 30 35 40 45
Time (min)

Figure 2.2: Chromatogram from the scat of a representative
female Minnesota Zoo otter showing a typical pattern of
peaks for females in this series.

25 30
Time (min)

Figure 2.3: Chromatogram from the scat of a group of female
otters at Marine World fed a diet of adult snakes.

10000 1o




0 5



25 30 35

Time (min)

Figure 2.4: Chromatogram from the scat of male otter, Toby,
showing the pattern typical of this animal and the Marine
World female group.




18 minutes but have a series of moderate to large peaks from

18 to 25 minutes. Most of the peaks in the group feeding

trial samples are after 19 minutes. The four chromatograms

from male Toby have from 46 to 103 peaks, with an average of

77.5 peaks per sample. The group feeding trial

chromatograms have from 8 to 58 peaks, with an average of

only 17.14 peaks per sample.

Individual Differences

The 60 Minnesota Zoo chromatograms, including 10

replicates from each of six otters, were used to test for

individual differences. These chromatograms are visually

very similar in overall appearance and in the location of

major peaks (Fig. 2.1 and Fig. 2.2). In all, 183 peaks were

identified in the 60 chromatograms using the labeling rules

outlined above. Sixteen of these 183 peaks are found in all

60 Minnesota Zoo runs, and another 14 are found in from 50

to 59 runs, revealing a total of 30 common peaks. At the

other end of the scale, 52 peaks are unique to a single run,

and another 53 peaks are found in 2 to 10 runs. Seventeen

peaks occur in 11 to 20 samples, 18 peaks occur in 21 to 30

samples, 5 peaks occur in 31 to 40 samples and 8 occur in 41

to 50 samples.

The frequency distribution of the peaks was used to

search for individual differences by two methods. First,

the 53 rare peaks occurring in from 2 to 10 samples were

examined to see if any were only found in replicate runs

from one individual otter. No individual "fingerprint"

peaks were found by this method, as all of the rare peaks

were found in chromatograms of more than one otter.

Individual animals might instead produce characteristic

mixtures of compounds that are common to all animals. In

the chromatograms, this would appear as consistent patterns

in the relative sizes of some of the common peaks. Such

subtle differences in combinations of peaks are much more

difficult to locate than the absolute presence or absence of

particular peaks.

To test this hypothesis, the data on the 30 common

peaks that were present in 50 or more of the Minnesota Zoo

runs were sorted by area percent. The resulting list was

scanned for clusters of runs on the same animals with high

or low relative amounts of any compound.

This analysis revealed seven peaks that are relatively

high or low in certain individual otters. A closer look at

these seven peaks, however, revealed no definite

consistencies in the peaks alone, or in ratio combinations

with other peaks. A principal component analysis of the

most common peaks also yielded no definite individual

differences. Although in this study no individual markers

could be determined, it is still theoretically possible that

further sophisticated statistical analyses might reveal some

differences at a later date.

Gender Differences

Since 30 of the 60 Minnesota zoo chromatograms

originated from otters of each sex, the search for gender

markers concentrated on those 22 peaks that occurred in 20


to 30 of the samples. None of these peaks was found

consistently only in females. Eight of these 22 peaks,

however, occurred predominantly in males (Table 2.1). Both

peaks M1 and M6 occur in a single chromatogram from female

35, and peak M5 appears once each in female 37 and female 82

chromatograms. The rest of the occurrences of these peaks

are seen only in male chromatograms. The other five peaks,

M2, M3, M4, M7 and M8 occur only in males.

It must be noted that not every sample from every male

contains these peaks, although they eventually appear in at

least one of the replicate samples from each male. Peak M3

is the most reliable, and is found in 96.7% of the 30

possible male samples. Peak M4 is next in reliability,

occurring in 93.3% of the males samples. The other three

male peaks, peaks M2, M7 and M8 only appear 86.7%, 80%, and

76.7% of the time, respectively.

When the 30 Minnesota male chromatograms are separately

examined, 14 of them contain all eight male peaks, seven

contain seven of the peaks, and four more contain six male

peaks. Thus, a total of 83.3% of the male chromatograms

contain at least six of the eight identified male peaks.

Only one chromatogram contains a single male peak. The rest

of the chromatograms (13.3%) contain from three to five male


In order to test the predictive value of these eight

male peaks, the four replicate samples of male otter Toby

and the four samples from three individual Marine World

Table 2.1: Male peaks in Minnesota Zoo chromatograms. Ten
samples from each of six Minnesota Zoo animals, three males
and three females, reveal certain peaks found predominately
in male chromatograms. The number of samples ("#samp") and
the percentage of 30 total samples (%) from otters of each
sex with these peaks are listed below.

Males Females

Peak Range in RT isam _% #samp % Notes

M1 14.558 to 14.803 22 73.3% 1 3.3% Female 35

M2 16.326 to 16.471 26 86.7% 0 0% All Males

M3 17.954 to 18.159 29 96.7% 0 0% All Males

M4 21.458 to 21.496 28 93.3% 0 0% All Males

M5 21.625 to 21.779 28 93.3% 2 6.7% Fem 37, 82

M6 23.345 to 23.597 19 63.3% 1 3.3% Female 35

M7 24.818 to 24.888 24 80.0% 0 0% All Males

M8 29.703 to 29.757 23 76.7% 0 0% All Males


females were examined for the presence or absence of these

peaks. The samples from male otter Toby contain all the

male peaks, Ml (in 3 samples), M2 (in 1 sample), M3 (in 4

samples), M4 (in 3 samples), M5 (in 3 samples), M6 (in 3

samples), M7 (in 2 samples) and M8 (in 3 samples). None of

the chromatograms from individual Marine World females shows

the presence of any peaks in any of these areas of retention

time. Once again peak number M3, found at retention times

from 17.954 to 18.159, proves to be the most reliable,

appearing in all four of the Toby samples.

Finally, chromatograms of the 35 group scat samples

from the five Marine World females were also scanned for the

presence of the eight male peaks. Although these

chromatograms have few peaks at retention times of less than

19 minutes, they do have quite a few peaks at later times in

the chromatograms where five of the male peaks occurred in

the Minnesota Zoo and Toby samples. No evidence is found in

any of these samples, however, of peaks M1, M2, M3, M4, M6,

M7, or M8. Peak M5, a peak that is found in two Minnesota

Zoo female samples, appears in one fish feeding trial

sample. This peak seems to be a less reliable indicator of

males than the other seven peaks.

Dietary Effects on Chromatograms

When the group of females from Marine World was fed

different diets, the chromatograms of their scat reveals a

wide variation in the number of peaks/sample (Table 2.2).

Table 2.2: Number of peaks in chromatograms of scat samples
obtained from otters fed different diets described in text.

Prey Item N Ranae Mean SD SE

Grass Shrimp 5 9-11 9.6 0.89 0.40

Crayfish 8 9-11 9.8 0.89 0.31

Fish 5 10-34 21.2 8.81 3.94

Crickets/Zoo Diet 5 13-19 15.8 2.17 0.97

Adult snakes/Zoo Diet 5 20-58 39.0 18.07 8.08

Day-old snakes/Zoo Diet 2 15-28 21.5 9.19 6.50

Zoo Diet 5 8-15 10.2 2.77 1.24

One-Way Anova Analysis

Source of Variation Sum Squares DF Variance Est.

Between Groups 3480.69 6 580.11

Within Groups 1759.60 28 62.84

TOTAL 5240.29 34

F = 9.23


Note: Number of samples (N), range in peaks per sample
(Range), mean number of peaks per sample (Mean), standard
deviation (SD) and standard error (SE) are reported for
chromatograms The one-way Anova test reports source of
variation, sum of squares, degrees of freedom (DF), and a
variance estimate.


The most peaks/sample are evident when adult snakes were fed

and the least are found with diets including grass shrimp, 1

crayfish or the standard zoo diet. A one-way Anova analysis

reveals that the differences in the number of peaks for

different diets was highly significant (p<.001).

Most of the peaks in all chromatograms are recorded at

later retention times (Fig. 2.3). Most peaks occur after

18.2 minutes in four fish samples and two samples of day-old

snakes; after 19.5 minutes in two cricket samples; and after

21.0 minutes in all the rest. The only earlier peaks appear

at 2.7 minutes in one crayfish and three adult snake

samples, at 3.4 minutes in three cricket samples, at 9.3 in

one grass shrimp, one crayfish and two cricket samples, and

at 15.8 minutes in one sample of day-old snakes.

In all, 117 peaks were identified in this data set.

Fifteen of these peaks are common to most of the 35 samples.

The crayfish and grass shrimp chromatograms, with the fewest

peaks overall, are mostly comprised of combinations of these

common peaks. At the other extreme, 52 peaks were

identified as unique to one or more samples of a single


The adult and day-old snake samples are the most

distinctive, containing 40 of the 52 diet-related peaks.

These seven snake samples are also distinctive in another

way, with a total of 22 peaks between retention times of

38.0 and 42.7 minutes. None of the other feeding trials

produced any activity in this area of the chromatograms.


Although the different diets are found to produce some

distinctive peaks, none of these is at the retention times

where male peaks have previously been noted. Even the many

unique peaks found in the snake trials are much later in the

chromatograms than any of the identified male peaks. These

results indicate that any peaks produced from the ingestion

of different diets do not obscure the presence of male



Male Peaks

The most important result of this study is the proof

that chromatograms of the volatile components in Asian

small-clawed otter scat can be used to distinguish males

from females. Certain chromatographic peaks are found

primarily in male samples. These peaks may represent male

steroids such as testosterone derivatives, or other

compounds that are metabolized in the presence of these

hormones, although definitive mass spectrometer tests were

not conducted in this study.

Until recently, most searches for the presence of

steroids in carnivores have been directed towards urine and

not feces. In one study (Raymer et al., 1986b) the volatile

components of male and female wolf urine were discriminated,

then castrated males and ovariectomized females were given

testosterone, progesterone or estradiol. It was found that

certain compounds associated with urine of intact males were


not found in urine of castrated males, although these

compounds would reappear in castrated males upon treatment

with testosterone. Ovariectomized females treated with

testosterone also produced some of these "male" compounds,

but at lower levels. Among the compounds found in greater

amounts in intact males or in neutered animals following

testosterone treatments were methyl propyl sulfide, methyl

isopentyl sulfide and four carbonyl compounds. Because

Asian small-clawed otters usually urinate and defecate

simultaneously, similar urinary volatiles may have accounted

for some of the male peaks found in this study.

Some of the male peaks may also be compounds that are

deposited in the feces along with waste products or as

secretions from the anal and proctodeal glands. Dr. Tim

Gross, at the Henry Doorly Zoo, Omaha, Nebraska, is looking

for sex steroids in the feces of Asian small-clawed otters

and in black-footed ferrets (Mustela nigripes). Preliminary

results (Gross, pers. comm.) show the presence of estradiol

and progesterone in female small-clawed otter scat, but he

has not yet looked for the presence of steroids in male

feces. In his extraction procedure, he uses methylene

chloride. It is likely that the male peaks extracted by

methylene chloride in this study could also be sex steroids.

If sex steroids like testosterone and testosterone-

influenced metabolites are indeed being detected, the choice

of Asian small-clawed otters for this study was fortuitous.

Most mustelids are seasonal breeders that only secrete large


amounts of testosterone when their testicles are enlarged

during their breeding season. In captivity, Asian small-

clawed otters breed throughout the year, with no peaks in

births evident during any season. Females have a minimum

interbirth interval of only ten months (Wilson et al.,

1991). When without a litter they cycle at approximately

four week intervals (Leslie, 1970). These otters are also

monogamous with a strong pair bond. Under these conditions

males probably have a more steady supply of testosterone

from one week to the next. In this study, the absence of

certain male peaks in particular individuals during some

sampling times could indicate low relative amounts of these

sex steroids. Overall, however, each male peak was present

from 63.3% to 96.7% of the time over a ten week period. In

other more typical mustelids with seasonal breeding,

testosterone and testosterone-influenced metabolites could

be expected to be at very low levels and undetectable by

this technique for many successive months.

The presence of male peaks Ml and M6 in single samples

from female 35, is also interesting. In the Minnesota Zoo

reproductive study that paralleled this one, two of the

three females were found to cycle normally, with definite

peaks in urine progesterone levels. Female 35, however, was

diagnosed as anestrous with a nonchromosomal genetic

abnormality (Binczek, pers. comm.). This aberrant female

apparently sometimes secretes male compounds, much as the


ovariectomized female wolves in the Raymer et al. (1986b)


Male peak M5, found in 86.7% of the male samples, was

also found in one sample from each of the two normal

Minnesota females, and in one of the Marine World female

group samples. This peak presumably represents a compound

more common in males, but occasionally secreted by normal

females as well.

No female peaks were identified in this study despite

the evidence that both estradiol and progesterone can be

extracted from feces of Asian small-clawed otters. If these

gender related peaks are present in this study but were not

detected, they might be hidden in areas of the chromatograms

where they are overshadowed by other larger peaks. A big

peak at a particular retention time could hide a smaller

peak in the same area and both would be considered to be the

same peak in this gas chromatographic analysis.

Alternately, if these peaks are highly volatile, they may

have dissipated before the scat samples were collected and

preserved. Test runs on pure samples of these hormones

would pinpoint the times at which they elute, and these data

would be useful to further studies to identify these peaks

in chromatograms of otter scat.

Individual Differences

Another goal of this project was to try to pinpoint

individual scent profiles of different animals. As in other


studies of carnivore scent marks, this study was

unsuccessful in this attempt. Gorman and Trowbridge (1989)

theorize that any individual carnivore "fingerprints" are

most likely due to differing proportions of the same mix of

compounds that all animals share and not to unique compounds

found in individual animals. Although these individual

"fingerprints" have not yet been found in any carnivore, it

is still theoretically possible that they do occur. More

work at a future date might reveal differences and

similarities among the complex mix of components present in

the scent of otter scat. Since otters can recognize

individuals of their own species from the scent in the scat

(Trowbridge, 1983), it is just a matter of time before our

own analytical tools can duplicate this task.

Variation in Number of Peaks for Different Diets

When different prey items were fed to the five female

otters at Marine World, the number of peaks in the resulting

chromatograms varied widely with the diet. A diet of

crustaceans, either crayfish or grass shrimp, resulted in

chromatograms with the fewest peaks. This may have been due

in part to the relative inertness of chitin in these scat

samples. Chitinous exoskeletons constituted a large portion

of the scat samples from both the crayfish and grass shrimp

feeding trials. When methylene chloride was added based on

the mass of the samples, the resulting extract was low in

chemical activity, and resulted in fewer chromatographic

peaks. Crayfish exoskeletons were thicker and heavier than


those of grass shrimp so the crayfish scat samples were

composed of more chitin by mass. The crayfish samples,

accordingly, had the smallest number of chromatographic

peaks. The snake chromatograms showed the greatest number

of unique peaks among the various feeding trials,

particularly in the latter portion of the runs. This may be

related to the observation of European otter surveyors

(Macdonald, pers. comm.) that otter scats containing snake

skin have a strong, "vile-smelling" odor. The musk glands

of adult water snakes may contribute to this smell and may

also have contributed to the large number of peaks found in

chromatograms resulting from an adult snake diet. These

musk glands are not developed in newly hatched snakes and

this may explain why the chromatograms of the otters' scat

following ingestion of this prey item revealed fewer peaks

than were seen in the case of adult snakes.

Despite the significant differences in the total number

of peaks in the chromatograms of otters fed different diets,

the location and sizes of the most common peaks were similar

in all trials. Except in the case of the adult snake

trials, where extra peaks were noted, the diet did not

change any of the major components of the chromatograms.

Even in the case of the snake trials, however, the observed

differences were in the latter portion of the runs, beyond

the areas where the male peaks were identified. These

results indicate that scat samples collected in the field

from otters eating different foods could still usefully be


compared for consistent similarities and differences in

their chromatograms.

Differences Between Runs

Although this study focused on the search for gender,

individual, and diet-related effects on the chromatographic

profiles of otter scat, other results became evident. One

of these was the basic observed differences between the

chromatograms from the Minnesota Zoo, Marine World and

Cheyenne Mountain Zoo. When the peaks were labeled, the

Cheyenne Mountain Zoo (Toby) and Marine World samples shared

116 peaks with Minnesota Zoo animals but 65 new peaks were

unique to Toby, 15 peaks were only found in Marine World

females, and 3 others were found in both Toby and Marine

World samples but not in Minnesota Zoo animals. In

contrast, the 60 samples that were all from the Minnesota

Zoo were consistent in both the number of peaks, and in the

retention times of most of these peaks.

Despite attempts to standardize the collection,

handling, preservation and preparation of all samples,

unavoidable differences occurred in the husbandry and

feeding routines and in the exhibit substrates in each of

the three zoos. For instance, the volatile components of a

scat sample scraped off a hollow log or a patch of grass are

probably different than those from a scat scraped off a

clean concrete floor. The time of day the otters are fed

and the exhibit is cleaned and what chemicals are used to


clean the exhibit may also affect the volatile components of

the scat. These slight differences in procedures may have

resulted in the observed differences in the chromatograms

among animals at different zoos.

For this reason, samples from animals from different

zoos could not be compared for individual differences. Any

peaks found only in otters from a particular enclosure could

be due to any number of factors other than inherent

differences in the scent produced by an individual otter.

For instance, the four chromatograms analyzed from Toby

contained a total of 65 peaks not found in chromatograms

from other otters. Instead of being evidence of individual

identity markers for this one animal, these peaks are

probably just compounds relevant to the diet and husbandry

of this otter at Cheyenne Mountain Zoo.

Aqing of Samples

Another result was the apparent effect of the time of

collection on the chromatograms of otter scat. This can be

demonstrated by comparing the chromatograms from the Marine

World female group and from individual members of this group

when all were fed the same standard zoo diet.

The Marine World individual samples and the group

samples from these same animals were very different. The

four individual chromatograms from three of the Marine World

females all had a number of early peaks but had relatively

few peaks in the later portion of the runs. The group


samples showed the opposite pattern, with few peaks in the

early half of the chromatograms and a relatively large

number of peaks at later times. These observed differences

between the individual and group samples from the same

otters may be a result of aging of the samples before they

were collected and frozen. Support for this explanation

comes from a comparison of the collection procedures for

these two sets of samples.

The samples from individual members of the female group

were collected opportunistically. The keepers happened to

be watching the female group, when a single otter defecated.

The keepers rushed into the enclosure, chased the other

animals away and collected the scat. This scat was

immediately labelled and frozen, in an extremely fresh


In contrast, the group female scats were collected from

the holding pen floor when the pen was cleaned around 1000.

These scats could have been deposited as early as 1600 the

evening before, when the animals were cleaned and fed for

the night. These group samples could have aged as many as

eighteen hours by the time they were collected and frozen.

Because this part of the experiment was conducted during the

summer, the afternoon temperatures were at least 260C.

Under these conditions, the most volatile compounds could

well have dissipated and other compounds may have decomposed

prior to the gas chromatographic analyses.


The most volatile compounds in a chromatogram elute

early in the runs. The lack of peaks in this portion of the

group female chromatograms may be a result of the

dissipation of these volatiles before the samples were

collected and frozen. The fresh-frozen individual otter

scats, however, still contained the more volatile compounds

that were evident as early peaks in the chromatograms. The

presence of peaks in the early part of these chromatograms

may thus be an indication of the freshness of these samples.

Another indication of the age of the samples may be

found by examining the number of peaks at later retention

times. It has been found through gas chromatographic

studies of the volatiles in mouse feces (Goodrich et al.,

1990) that the chemical composition of freshly voided feces

and feces that have aged for 24 hours are somewhat

different. The amounts and combinations of compounds at

later times in the chromatograms intensify with age. Many

of the compounds identified in the fresh samples were found

in the aged samples but some of the volatile fatty acids

were found in higher amounts in the aged samples. Certain

new compounds were only present in the aged samples. This

aging of samples is probably due in part to bacterial

decomposition of the feces.

When the individual Marine World chromatograms are

compared with the group chromatograms, this trend is also

evident. The fresher individual samples had fewer peaks in

the later portions of the chromatograms, in contrast to the

more aged group samples that had many late peaks. Together


the presence of more early peaks and fewer later peaks may

indicate samples that were frozen while still fresh.

Samples that have aged seem to show the opposite pattern of

few early peaks and more later ones.

Luckily the absence of the most volatile compounds in

the aged samples may not negate the usefulness of these

samples for conveying information on the identity of the

scent-marker. It is thought that the more volatile

compounds excreted by mammals are used for short term, long

distance signalling and that the less volatile compounds are

more useful at close range where they can be sniffed for a

longer period of time (Muller-Schwarze and Houlihan, 1991).

These researchers hypothesize that, in the case of beavers,

the more volatile compounds attract conspecifics to the

scent mounds, but the less volatile compounds hold the keys

to gender, individuality, reproductive status and other

communication signals. This may also be true of the otters

in this study.

The changes in the smell of scent marks and urine over

time are probably detectable by various species. For

instance, it has been shown that dwarf mongooses can

discriminate between fresh and older samples of scent marks

(Rasa, 1973) and that male guinea pigs can discriminate

between varying ages of urine (Wellington et al., 1983).

These olfactory cues may provide animals with useful

information regarding the time of passage of the animals

leaving the scent marks and may aid in the maintenance of

territoriality. Similarly, the overall changes in the


chromatograms between fresh and older scats might also give

a field researcher an indication of when the scats were


Potential Field Applications

This study with captive Asian small-clawed otters

demonstrates that important information on the gender of the

otter and the age of the sample can be extracted from the

scent. This information could provide another window of

insight on the ecology of wild otters in the field in

Southeast Asia. Knowing the gender of individual otters

leaving scats could help answer some questions of dispersal

and group cohesiveness. Are single scats at a distance from

the group toilet sites representative of males dispersing?

Are there any same-sexed groups or are they composed of both

sexes? Do the otters leave their scats in the early night

or closer to the morning? Can any patterns of the movements

of the animals be charted by noting the age of the samples?

These and other questions might be addressed, if this

technique works in the field. The fact that the gender and

temporal information was evident in scats even when the

otters were fed different diets also points to the possible

utility of this technique to field studies.

It is also possible that this technique could help

differentiate the species of otter depositing scats, where

two species are sympatric and tracks are difficult to find.

Known samples collected from smooth otters (Lutra

perspicillata) in Asian zoos might reveal differences in the


chromatograms of their scat as compared to that of the Asian

small-clawed otters (Aonvx cinerea) in this study.

Unfortunately, in the field there are a number of

additional complexities that may affect a gas

chromatographic analysis of otter scat. Samples will

necessarily be collected from different substrates, varying

from vegetation to dirt to rocks, which may affect the

scent. Under field conditions, freezing samples may be

impossible and maintaining them in an ice chest for long

periods of time may change the scent. Other unforeseen

factors may further complicate the issue. Until this

technique is tried under field conditions, however, we will

never know if it will work. These field trials form the

basis of the next chapter.



Little is known about the behavior and ecology of Asian

small-clawed otters (Aonvx cinerea) and smooth otters (Lutra

perspicillata) throughout their range (see Chapter One).

They are often elusive and difficult to observe in the wild.

Like most otters, however, they deposit their feces in

obvious locations, where it is easy for other otters, or

otter researchers, to locate. These feces can provide

valuable information on the ecology of otters that cannot be

determined by rare direct observations of the animals'


The information contained in otter scat is used to

learn more about these two otter species in this study.

In this chapter, I present the results of visual and gas

chromatography analysis of smooth and small-clawed otter

scat from a Malaysian study site. In the following chapter,

I present information on the foraging ecology of these two

otter species as determined by the examination of prey

remains in scats. Together, these two chapters yield

biological information with conservation implications

outlined in the concluding chapter of this dissertation.


In the previous chapter I determined that, under the

controlled conditions of captivity, male and female small-

clawed otters can be discriminated by the volatile

components in their scat. In this chapter, the volatile

components in scat samples obtained from known smooth and

small-clawed otters in Asian zoos are examined for species-

specific differences. The utility of the gas chromatography

analysis is then tested in the field. Simultaneously I

collected information on the group size and scent-marking

activities of both otter species by occasional observation

of otters and by visual analysis of signs at their toilet



Study Site

All samples were collected in a 6 km2 area of

cultivated rice fields and adjacent mangroves and mudflats

on the west coast of the Malay Peninsula near the town of

Tanjong Piandang, in the northwest corner of the state of

Perak, Malaysia (5003' N, 100025' E). The study site (Fig.

3.1) is diked, canalized and irrigated. Two crops of rice

are harvested each year on a schedule posted at the entrance

to the area. The western side of the study site is bordered

by a coastal mangrove forest approximately 0.5 km wide. Two

canalized rivers, Sungei (River) Labu and Sungei Betel Atas,

form the northern and southern borders of the study site.

Beyond the manually-operated watergates, the rivers run









Figure 3.1: Map of the study site at Tanjong Piandang,
Perak, Malaysia. The letters A through G indicate toilet
sites described in the text.


through tidally influenced mangroves and mudflats and empty

into the Straits of Malacca 0.75 km away. The mudflats near

both water gates are inhabited by many species of crabs

(mostly families Grapsidae, Ocypodidae and Paguridae) and

mudskippers (Gobioidei). The southern border of the study

area is defined by a major highway between the towns of

Tanjong Piandang and Parit Buntar.

The rice field site is bisected north to south by a

dirt road originating at the Tanjong Piandang/Parit Buntar

Highway, and extending 3.5 km north to the mangrove fringe,

where it forms a T. The left fork of the T follows the

mangrove fringe 0.7 km to the water gate at Sungai Betel

Atas. The right fork follows the mangrove fringe 0.6 km to

the water gate at Sungai Labu. From here a 0.5 km walking

path follows the west side of the tidal river from beyond

the water gate north to where it empties into the Malacca

Straits. Both species of otters deposited most of their

scat along these roads, especially near conspicuous

landmarks, such as road intersections and water gates.

Accordingly, the existing system of 5.3 km of roads and

paths formed the transects for this study.

Collection Schedule

Four six-week-long collection trips were made to the

Malaysian study site, in April/May 1989, July/August 1989,

November/December 1989, and May/June 1990. The spacing of

these visits was intended to cover the variable high and low

water levels and resulting rice harvest and planting cycles.


The fields were irrigated in December 1988, July 1989, and

February 1990 and were drained for harvest in May 1989,

December 1989, and July 1990. During the July/August 1989

collection trip the fields were being irrigated and a new

crop of rice was being planted. During the May/June 1990

trip the rice was midway in its growing cycle and the water

levels were relatively high. The water levels were at their

highest during the April/May 1989 trip. During the

November/December 1989 visit the fields were being drained

and the rice was being harvested. The varying levels of

water in the canals affected the distribution and abundance

of the fish species within the water system, and thus the

prey of the otters in this region.

Field Samples

All smooth and small-clawed otter signs were recorded

each morning along the 5.3 km transect. Estimates were made

of the size of groups based on numbers of scat piles and

related tracks. Notes were made on the amount of smearing

of the scats as an indication of the otters' scent-marking

behavior. Only those toilet sites with well-defined tracks

were given a species designation in the field notes and were

included in the data. The principal toilet sites and

landscape features are diagrammed in Fig. 3.1. Fresh scat

samples that were accompanied by good diagnostic tracks were

collected from these toilet sites for the gas chromatography



Occasionally otters of both species were observed in

the study site or in nearby rice fields or mangrove canals.

During the first trip I spent a number of nights roaming the

study site, but observations were rare, brief and

uninformative, so this process was discontinued. Throughout

the rest of the study, field notes were maintained on all

opportunistic otter sightings, but no concerted effort was

conducted to observe them. All of these sightings occurred

either at the study site, near the house we occupied in the

Tanjong Piandang rice fields during the third and fourth

trips, or at the Kuala Gula Wildlife Sanctuary field station

in a mangrove/oil palm habitat approximately 80 km away.

The sightings are described in Appendix B.

Captive Samples

Samples were also collected from captive otters in

Malaysian and Thai zoos. These animals were housed either

individually or in groups. Individual samples from otters

maintained in groups were obtained with the vigilance and

help of the local keepers. All samples obtained from zoo

otters are listed in Table 3.1.

Preparing and Analyzing Gas Chromatography Samples

All scat samples from the field or from captive otters

were prepared identically. The samples were scraped into

inert glass vials and an equal amount of methylene chloride

by weight was added. After 24 hours, a small amount of the


Table 3.1: Scat samples collected from Asian
for gas chromatography analysis.

zoo otters











































NOTE: The species are small-clawed ("smcl") or smooth
otters and the dates (listed by MM/DD/YY) are when samples
were collected.


Tanjong Piandang

Tanjong Piandang

Taiping Zoo

Zoo Negara

Melaka Zoo

Zoo Negara

Zoo Negara

Zoo Negara

Taiping Zoo

Bang Phra Zoo

Bang Phra Zoo

Crocodile Farm

Safari World


Born 7/89

Born 11/89

Female and




of pair

Male of pair







extract was removed with a sterile disposable pipette and

placed in an amber gas chromatography vial for later

analysis in the United States.

During the first three study visits, these extracts

were held in an ice chest for the duration of the time in

the field. On the last trip (May/June 1990), following the

experiments described in the last chapter, the storage

protocol was improved. Although the scent samples were

still by necessity held in an ice chest for a few days, they

were transferred to a freezer as soon as possible. The

samples were transported to the United States in the ice

chest but they were placed in a hotel freezer during the

times in transit in Kuala Lumpur or Bangkok.

All gas chromatography analyses were conducted by the

Chevron Labs, Richmond, California, as described in the

previous chapter. The samples from the first three trips

were refrozen for periods of up to a month before they were

run in two batches with other accumulated samples from U.S.

zoos. The samples from the last field trip were run in a

single batch immediately upon being transferred to Chevron.

Peak Analyses

The gas chromatography data were analyzed in three

stages. First the data were sorted by numbers of

peaks/sample to look for consistencies and differences in

peak numbers between samples and batches. Next, the data

were examined for species-specific differences. The common

peaks in this data set were labelled and numbered according


to the rules in Chapter Two. The resulting data were

searched for the presence of particular peaks or patterns in

relative peak areas associated with only one species.

Finally, to see if males could be discriminated from

females by the presence of certain "male" peaks, I looked

for the eight male peaks identified in Chapter Two in all

samples from all trips. Samples containing these peaks were

then examined to see if they represented known males,

females or wild samples.


Field Sightings

I saw otters opportunistically and repeatedly during

the study. Groups of smooth and small-clawed otters were

observed near the field station at Kuala Gula and in the

study site. Another group of small-clawed otters was also

observed near our house outside the town of Tanjong

Piandang. These observations are detailed in Appendix B.

Visual Analysis of Toilet Sites

Group sizes

Confirmed smooth otter scats were located on 21

occasions within the study site. Only once was a single

scat deposited; groups of two or three otters were recorded

six times. The rest of the scats indicated groups of four

or more otters. Two of these toilets showed evidence of use

by groups of more than ten otters.


The small-clawed data were similar (Fig. 3.2). Seven

scats were found singly, and another 21 toilet sites

indicated groups of two or three otters. Seven toilet sites

revealed the presence of more than ten otters. The rest of

the 63 total small-clawed sites indicated from four to ten

animals in the group. When the smooth and small-clawed data

were compared in a Chi-square analysis, the difference in

group sizes between these two species was not found to be

significant (p<0.997).

Scat smearing

Only small-clawed otters smeared their scat at the

toilet sites. Scat-smearing was found in 28 of the 63

positively identified small-clawed otter toilet sites,

compared to none of the 21 positively identified smooth

otter toilet sites, a highly significant difference

(p<0.001) by Chi-square analysis.

Most of the small-clawed otter scat-smearing occurred

during the second trip, with 12 out of 18 sites showing

smearing (Fig. 3.3). The least amount of smearing was found

in the third trip, with only seven out of 27 sites showing

smearing. In both the first and third trips exactly half of

the sites showed smearing. The differences between trips,

however, were not found to be significant (p<0.072) when

subjected to Chi-square analysis.

The presence of smeared scat was related to the size of

the small-clawed otter groups (Fig. 3.4). In groups of

seven or larger, more toilet sites were smeared than not

Percent of Occurrences








Group Size

M Smooth otters

EM Small-clawed otters

Figure 3.2: The estimated sizes of groups of small-clawed
and smooth otters based on the scats and tracks at the
toilet sites.

1 2-3 4-5 6-7 8-9 10 >10

Number of Scat Sites







Third Trip Fourth Trip


M Smeared Scats

M Unsmeared Scats

Figure 3.3: The number of small-clawed otter toilet sites
showing smearing during each of the four study visits
described in the text.

First Trip Second Trip
First Trip Second Trip

i :g

Number of scat sites


7-9 10+

Group Size

M Smeared Scats

M Unsmeared Scats

Figure 3.4: The amount of smearing at small-clawed otter
toilet sites based on the estimated size of the group.


20 h


10 -


0 L



smeared. Groups of three or fewer rarely displayed

smearing. Chi-square analysis revealed that there were

significant differences (p<0.001) in the amount of smearing

based on group size.

The presence of smeared scat also varied among the

different locations (Fig. 3.5) with the most occurring at

Sungai Labu ("C" in Fig. 3.1) and the least at Point Labu

("D" in Fig. 3.1). The differences among these sites were

found to be significant (p<0.002) by Chi-square analysis.

Gas Chromatoqraphy Analysis

Description of chromatoqrams

A total of 60 gas chromatography samples were collected

and analyzed from the four research trips to the field.

Eight of these samples were from small-clawed and 16 were

from smooth otters held in Malay and Thai zoos. The rest of

the samples were collected from smooth otters (13 scats) or

from small-clawed otters (23 scats) in the study site at

Tanjong Piandang. Twenty-nine of the samples were obtained

during the first three trips. The remaining 31 samples were

obtained during the fourth trip. These fourth trip samples

included captive and wild otters of both species. Three of

the 12 small-clawed samples from the fourth trip were from

captive otters, including two from "Jambu" and one from

"Pit-Pit." Of the 19 smooth samples from the last trip, 13

were from captive otters, representing all animals listed in

Table 3.1.

Number of Scat Sites

Road "T" Second Road Betel Atas Point Labu Sungal Labu

Site Locations

M Smeared Scats

M Unsmeared Scats

Figure 3.5: The presence of smeared small-clawed otter scat
based on the location of the toilet sites.











The 29 samples obtained during the first three trips

are very different from the 31 samples that were collected

during the fourth trip. These early samples have a range of

from 35 to 191 peaks/chromatogram, with an average of 100.8

peaks/chromatogram. In contrast, the fourth trip samples

have far fewer peaks, ranging from 10 to 40 peaks per

sample, for an average of only 17.2 peaks/chromatogram.

The pattern in peaks were examined for the

characteristics of "aging" described in Chapter Two.

Samples from the fourth trip show evidence of this aging

pattern, with few early peaks evident in 28 of the 31

samples (Fig. 3.6). The samples from the first three trips,

in contrast, show another pattern of peaks. Twenty-four of

the 29 samples from these early trips have many peaks

throughout the chromatograms, with many large peaks at early

retention times (Fig. 3.7). This pattern is unusual when

compared to the controlled captive samples that are analyzed

in Chapter Two.

Species differences

When the complete data set is sorted by retention time

and the peaks are identified according to the rules outlined

in Chapter Two, no particular peaks are found that are

associated with only one otter species. Seventeen common

peaks that occur in 30 or more of the 60 samples are

identified. When these data are sorted by area percent, no

otter species is found to be characterized by either high or

low relative amounts of any of these peaks.



II -





0 5

Time (min)

Figure 3.6: Sample chromatogram from the fourth trip.






0 5 10 15 20 25 30 35 40 45
Time (min)

FiQure 3.7: Sample chromatogram from the first trip.

Since the fourth trip samples are more consistent than

those collected in previous trips, this data subset is

analyzed separately. Seven of the 17 common peaks are found

in 28 or more of the 31 fourth trip samples. Once again,

the relative area percent of these peaks is not a useful

species indicator. None of the rarer peaks that occur in

more than four samples is uniquely associated with either

otter species. When the data from known captive individuals

from the fourth trip are examined separately both for the

presence or absence of particular peaks, or for the presence

of high or low area percent of common peaks, again no

species indicators are identified.

In summary, no species-indicators are present in either

the absolute presence or absence of certain peaks, or in the

relative area percent of the most common peaks when the

data for the two species are compared. This result is

evident in the entire data set, in the fourth trip data and

in the data from known individual captive otters from both


Male peaks

The chromatograms from all 60 samples from Asia were

searched for the eight male peaks identified in Chapter Two.

In all, 26 samples (43%) contain one or more of these peaks.

Peak M3, the most common male peak in the Minnesota Zoo

data, was found in 22 of these 26 samples. The other peaks,

in order of frequency of occurrence in the samples were M6

(15 samples), M5 (14 samples), M1 (12 samples), M4 and M7

(11 samples each), M2 (10 samples), and M8 (4 samples).


In the complete data set, most of the 26 samples that

contain these peaks have only a few of them. Nine of these

samples contain only one peak and two others contain three

peaks. Ten samples have four or five peaks, and four have

six peaks. Only one sample, from a wild small-clawed otter,

has all eight peaks. In summary, only 19.2% of those

samples with male peaks have six or more of them, in direct

contrast to 83.3% of the Minnesota Zoo male chromatograms

that contain this many male peaks.

A subset of the data including known captive male

samples was tested separately for the presence of the eight

male peaks identified in Chapter Two. A total of 14 samples

were obtained from known captive male otters, representing

duplicate samples from four smooth males and two small-

clawed males (Table 3.1). Five of these samples were

obtained during the first trip and the rest were obtained

during the fourth trip. Four of the five first trip male

samples were from captive male/female pairs (ZNG and ZNP)

and the fifth was from a smooth male (TZM).

When all 14 captive male samples were tested for the

presence of the eight male peaks identified in Chapter Two,

the results were disappointing. The only samples containing

a number of the identified male peaks are those from the

first trip. The five samples from ZNG, ZNP and TZM all

contain four or more male peaks. A sample from a female and

baby (TF) from this trip also contains three of these peaks.

These peaks in these first trip samples are probably an


artifact of deterioration, as described above, and not the

actual presence of male markers.

Only two of the nine known male samples from the fourth

trip have any of the identified male peaks. One of the two

samples from a juvenile small-clawed otter (Jambu) contains

peak M4 and a single sample from an adult smooth otter (TZM)

contains peak Ml. The six other smooth male otter samples

from the fourth trip contain no male peaks. Seven fourth

trip samples from known captive females also contain no male


Fifteen field samples were also collected during the

fourth trip, including nine from small-clawed otters and six

from smooth otters. Peaks M3 and M5 are found in two wild

small-clawed samples. Based on the Minnesota Zoo control

data, where 97% of the male samples had three or more of the

eight male peaks, it is unlikely that a male would contain

only two of these peaks. None of the other samples contain

any of the identified male peaks.

In conclusion, it is unlikely that male otters are

reliably detected by this gas chromatography analysis. Most

of the male peaks identified in the entire 60 sample data

set are in samples from the early trips that had probably

deteriorated due to inadequate preservation techniques. The

fourth trip samples, however, contained few male peaks, even

among known captive male otters. Although the sex ratio of

wild smooth or small-clawed otters is unknown, if males were

reliably determined by these peaks, at least one of the


fifteen field samples should have been a male with more than

two of these peaks.


Scent-Marking Displays

Smooth otter toilet sites never showed indications of

scat-smearing. On the few occasions when groups of three or

five of these otters were observed, all otters defecated

simultaneously but none engaged in scat-smearing behavior.

Scat smearing has also never been reported for this species

in captivity.

Small-clawed otters, in contrast, smeared their scat at

28 of the 63 toilet sites. This scat-smearing is most

likely associated with scent-marking displays. This

behavior was not directly observed in the wild, although it

is often observed in captive groups. The only time a small-

clawed otter was seen defecating in this study it was alone

and did not smear its scat. The observations of increased

scat-smearing with larger groups may indicate the social

facilitation of this behavior.

More scat-smearing was observed at the Sungai Labu gate

(site "C" in Fig. 3.1) than at the mouth of the river (site

"D"). Site "C," bordered by mudflats on one side and the

freshwater canal and rice fields on the other, is often used

by both otter species. Site "D," a mudflat and mangrove

habitat, is used only by small-clawed otters. Increased


scat-smearing in the shared area may be a scent-marking

display with interspecies territorial implications.

In captivity, small-clawed otters are often observed in

scat-smearing displays. Typically, scat is smeared with the

hind feet and the tail and all otters in the group

participate in a frantic manner. Presumably this scat-

smearing behavior involves scent-marking that uses the fecal

piles as a vehicle for deposition of more scent from the

anal glands. This behavior deserves more study in

captivity, before its function can be adequately assessed.


No seasonality was observed in the scat-smearing

behavior. Smeared small-clawed otter toilet sites were

found in all study periods. Seasonality was also not

readily apparent in the observations of small-clawed otter

cubs. Based on the estimated dates of birth of cubs

observed in this study, small-clawed otters were born in

July (one instance) and in November (two instances). Small-

clawed otters in United States zoos also show no seasonality

in their births (Enger, 1991).

Smooth otters in this area also did not show a definite

season of more births. Estimated dates of birth of smooth

otter cubs seen or heard in this study are April 1989, July

1989 and November 1989. At the Delhi Zoo, captive births

were also recorded year-round (Naidu and Malhotra, 1989),

showing no seasonality. Matings were only observed from


August to November, thus opening the possibility of delayed

implantation with this species. More captive and field data

are needed to address further the issues of delayed

implantation and seasonality of births in smooth otters.

Utility of Gas Chromatography Technique in the Field

Gas chromatography analysis of otter scat collected in

Southeast Asia was found to have little utility in this

pilot study. Unlike control samples from captive otters in

United States zoos, these field samples contained few of the

male peaks identified in Chapter Two. Few of the samples

that contained any of these peaks contained six or more of

them. Little about the gender of the animals could be

reliably inferred from these results. Preliminary

investigations to determine the species of the otter from

Asian scat samples also yielded no useful results. No

species-specific peaks or common peaks that were larger or

smaller in a given species were located in this study.

Quite likely, the failure of this pilot study lies in

the techniques for preservation of the samples in the field.

The samples from the first three trips were very

inconsistent, with few common peaks and many unique ones,

and a large number of peaks per sample. These samples were

maintained in an ice-chest and not frozen for up to a month

in the field. This technique almost certainly led to severe

degradation of the samples before they were analyzed in the

United States.


The storage protocol was improved by the fourth trip,

and the samples were placed in a freezer whenever possible.

Unfortunately, they were still carried in the ice-chest

whenever they were moved. It was determined in Chapter Two

that those samples that had aged before being frozen changed

in character, with fewer early peaks and more peaks at later

retention times. The fourth trip samples showed a similar

pattern with only an occasional rare peak at early retention

times, and few peaks overall. The fourth trip samples from

smooth otters at Crocodile World, Bang Phra Open Zoo, Safari

World and Zoo Negara all revealed this aging pattern even

though these samples were collected immediately after the

otter defecated. The aging seen in the fourth trip samples,

then, was not due to the time elapsed before collection, but

was probably due to the degradation of the samples when they

were repeatedly thawed and refrozen during transit.

Both of these storage protocols appear to be inadequate

for a gas chromatography assessment of the volatiles in

otter scat samples. Until better techniques can be

formulated to freeze samples immediately and completely in

the field, this technique will have limited practical

utility to studies of otters or other species in the wild.

Further Investigations

Two other experimental techniques not attempted in the

present study may be alternative ways to identify the

species and gender of wild Asian otters. Preliminary


reports from Dr. Tim Gross, of the Henry Doorly Zoo, Omaha,

Nebraska, indicate that the sex and reproductive condition

of certain carnivores, including Asian small-clawed otters,

can be determined by direct extraction of hormones in their

scat. This technique, if it works with samples that are

kept cool, but unfrozen, might be another approach to field

work questions.

Similar sympatric carnivore species can also sometimes

be discriminated by the bile acids in their scat (Major et

al., 1980; Johnson et al., 1984). These scats do not have

to be frozen to be analyzed for these substances at a later

date. It remains to be determined if this technique will

discriminate the Asian otter species.

I hope that refinements of the gas chromatography

procedure and other techniques will someday give the field

researcher a better understanding of the behavior and

ecology of elusive species like the Asian otters. Until

then, we must continue to rely on the time-honored field

techniques of counting tracks and scats, and hoping for

occasional glimpses of animals engaged in their daily




Hundreds of papers have been written on the diet and

foraging ecology of otters, especially European otters

(Lutra lutra) and North American otters (L. canadensis) (see

reviews in Harris, 1968; Chanin, 1985; and Mason and

Macdonald, 1986). The main purpose of this study is to

gather similar information on the foraging ecology of two

little studied otter species, the smooth otter, Lutra

perspicillata and the small-clawed otter, Aonvx cinerea.

Only two studies have been published on the diet of any

Asian otter species. The first is a study of the smooth

otter, in the Royal Chitwan National Park, Nepal (Tiler et.

al., 1987). For four months these researchers collected

smooth otter scats from eight segments of the Narayani River

and analyzed the scats for prey remains. They also studied

regurgitated pellets from fish-eating birds for comparison.

Although smooth otters were found to be primarily fish-

eaters, they also consumed frogs, shrimp, crabs, snakes and

mammals. When the diets of otters and fish-eating birds

were compared, otters were found to eat fish with a wide

range of vertebral diameters, whereas birds specialized on


small fish with vertebrae less than 2 mm in diameter. The

diet of the otters was found to vary with the topography of

the river. In high-banked, deep sections of the river that

were off-limits to fishermen, the smooth otters ate

predominately fish. In other sections, where the river

meandered through islands and channels accessible to

fishermen, the otters ate many more frogs and other non-fish

items. The researchers speculated that this divergence from

a piscivorous diet in the meandering portions of the river

was due to two factors: increased competition with human

fishermen and the presence of rock-bottomed pools that

provided a more suitable habitat for frogs and crustaceans.

A second study on the diet of small-clawed and smooth

otters has recently been published (Nor, 1989). This study

reports on the analysis of prey items from fifty scats of

both otter species in our study site in Tanjong Piandang,

Perak, Malaysia. He found that fish (of undefined species)

made up most of the diet of both otter species and that both

also ate mollusks and insects. Only small-clawed otters

were found to eat crabs, and only smooth otters were found

to eat mammals. Unfortunately, details of the methodology

were vague, and it was unclear when and exactly where the

scats were collected.

A second purpose of this study is to gather information

on the diet of wild small-clawed otters that might help

explain the urinary calculi (kidney stones) problem with

this species in captivity (Calle, 1988). Two-thirds of the

captive United States population of small-clawed otters have

calcium oxalate kidney stones. These urinary calculi are

the principal cause of death of these otters in captivity.

Detailed analysis of the studbook reveals no evident genetic

trends, and an improper captive diet is thought to be the

cause. Once the diet of wild small-clawed otters is

ascertained, a better captive diet can be formulated (see

Chapter Five).

Another aim of this study is to examine the potential

competition between two otter species in the same habitat.

Studies addressing the presumed competition of river otters

with fishermen are summarized in Harris (1968) and Mason and

Macdonald (1986). By and large, otters were found to

consume mostly bottom-feeding, slower-moving "trash" fish

and not the trout and salmon preferred by humans.

Only a few studies have focused on competition of

otters with non-human species (Erlinge, 1969; Rowe-Rowe,

1977a; Duplaix, 1980; Melquist, et al., 1981; and Wise et

al., 1981). Duplaix (1980) found that both giant otters

(Pteronura brasiliensis) and the much smaller southern river

otter (Lutra longicaudis) coexisted along the same stretches

of river in Surinam. By analyzing the prey contents in

scats of both species, she found that there was little diet

overlap. The smaller otter ate smaller fish than did the

giant otter.

Melquist et al. (1981) compared the diet of the native

North American mink (Mustela vison) and the North American

otter (Lutra canadensis) in Idaho, where they are sympatric.

Fish was the greatest prey item of overlap between the mink


and otter, occurring in 59% of 657 mink scats and 90% of

1902 otter scats. Both predators utilized small cyprinids,

but only the otters caught the larger fish species like

northern squawfish (Ptychocheilus oregonensis) and large-

scale suckers (Catostomus macrocheilus).

Both Erlinge (1969) and Wise et al. (1981) looked at

the overlap in the diet of European otters and introduced

North American mink (Mustela vison) where they coexisted.

Both studies assessed whether the decline in otter

populations was a result of the establishment of feral mink

populations from mink farm escapees. The Erlinge (1969)

study in southern Sweden demonstrated an approximate 60% to

70% overlap in the diets of both predators, depending on the

time of year. The greatest overlap was in winter, when both

species ate mostly burbot (Lota lota), pike (Esox lucius),

trout (Salmo trutta) and, especially for the otter,

cyprinids (family Cyprinidae). Even when the same fish

species were taken, however, the size of the minks' prey was

smaller than that of the otter. Also, mink did not utilize

habitats preferred by the otters, such as the wide parts of

the river that are rich in cyprinids. The diet of otters in

areas with mink and without mink was found to be similar.

Erlinge hypothesized that mink and otters had different

adaptations to catching different types of prey and that

there was some level of interference by the otter towards

the mink in preferred habitats. Competition by the mink,


however, was not thought to be a contributing factor to the

decline of the otter in Sweden.

A similar study in Devon, England compared the diet of

European otters and North American mink in a eutrophic lake

and a moorland river (Wise et al., 1981). At both sites,

the diets of both predator species overlapped by about one-

third. The mink was a generalist that ate more birds,

mammals and terrestrial prey than the otter, which was

largely a fish specialist. Once again, the greatest overlap

in the diets of both species was in the colder months, when

both relied to a greater extent on fish. These authors,

like Erlinge, concluded that competition with the introduced

mink was not a factor in the decline of otter populations.

Rowe-Rowe's diet studies (1977a, 1977b) of sympatric

spotted-necked otters (Lutra maculicollis) and clawless

otters (Aonvx capensis) in South Africa are the most

relevant to this dissertation. The clawless otter is in the

same genus as the small-clawed otter (A. cinerea) with

similar hand-like paws used to capture prey. The spotted-

necked otter is similar to the smooth otter (L.

perspicillata) with heavily-webbed front paws and mouth-

oriented prey-capture behavior. The pair of sympatric

African otters differs from the two Asian otters primarily

in size. A. capensis is a large animal up to 158 cm in

total length (head, body and tail), while L. maculicollis is

much smaller, with a total length of less than 107 cm

(Harris, 1968). With the two Asian otter species, the


situation is reversed. In this case, the Lutra species is

the larger of the pair, with the total length of L.

perspicillata reported up to 122 cm, while A. cinerea only

reaches a recorded length of 94 cm and is usually much

smaller than that (Harris, 1968).

Rowe-Rowe (1977a) compared the diet of both African

otters in two habitats that differed largely in the presence

or absence of trout. Amphibian remains were found in from

20.2% to 27.8% of the scats of both otter species in both

habitats. The relative use of crabs and fish, however,

differed between the two otter species. Clawless otters ate

the most crabs and the least fish in both habitats.

Depending on the habitat, from 64.0% to 67.8% of the

clawless otter scats contained crab remains, compared to

only 2.8% to 8.3% of these scats with fish remains. The

spotted-necked otter also ate substantial amounts of crabs,

with these remains found in from 30.6% to 39.2% of the

spotted-necked otter scats. Fish remains were found in from

30.6% to 39.2% of the spotted-necked otter scats. Rowe-Rowe

conjectured that the spotted-necked otter is largely a fish

specialist that had adapted to the abundance of crabs in his

study sites. Overall, the diet of these two otters

overlapped by about 66%.

The water mongoose, Atilax paludinosus, also inhabited

these sites. It fed chiefly on crabs, small mammals, birds

and frogs, and its diet overlapped that of the otters by 58%

to 66%. Despite this high degree of dietary overlap, the