Sirenews (ISSN 1017-3439) appears twice a year
in April and October and is edited by Daryl P. Domning,
Department of Anatomy, Howard University, Washington, D.C. 20059 USA
(fax: 1-202-265-7055). It is supported by the U.S. Marine Mammal Commission
and Sea World, Inc.
NUMBER 25 APRIL 1996
IN THIS ISSUE: MASSIVE MANATEE DIEOFF IN FLORIDA (p.
ON CULTIVATION GRAZING BY DUGONGS (p.
WHEN SEACOWS WALKED ON FOUR LEGS (p.
EDITORIAL: BAD NEWS OR GOOD?
Several significant developments for Florida manatees have occurred since our last
issue. One is the publication of the workshop volume on manatee population biology edited by
Tom O'Shea, Bruce Ackerman, and Franklin Percival (see Recent Literature, below). The
upshot of the two decades of painstaking work summarized in this impressive compilation is
that Florida manatees actually seem to have increased in numbers since protective efforts were
begun. At the end of the volume, O'Shea and Ackerman conclude that "the increases in
numbers of manatees counted in aggregation areas in winter reflected an increase in the Florida
population from the 1970's through the 1980's .... We are uncertain whether such a trend
continued in the 1990's." Furthermore, "Reproduction parameters revealed by studies
presented in these proceedings ... indicated the potential for more rapid growth than previously
recognized": as high as 7% per year at Crystal River. "This higher potential for population
growth makes the probability of true population growth in other areas during the 1970's and
1980's more plausible than previously thought...."
These conclusions were promptly underlined by the results of two statewide aerial
surveys conducted by the Florida Department of Environmental Protection after cold fronts in
January and February 1996: total counts of 2,274 and 2,639 manatees, respectively. These
numbers are dramatically higher than the previous high count of 1,856, made in 1992; and as
minimum estimates of actual manatee abundance, they show that the true population size is
closer to 3,000 than to the figure of 2,000 routinely quoted in recent years. Although survey
coordinator Bruce Ackerman noted in a press release that weather conditions nearly perfect for
counting manatees accounted in part for this result, the evidence for a growing manatee
population seems to be mounting.
What are we to make of this? Is the manatee population on the road to recovery and
removal from the endangered species list? Have all the protective regulations had their desired
effect, so that no further constraints on boaters or developers are needed? If manatee numbers
have grown along with human numbers in Florida, does that not show that human population
growth is harmless to wildlife, maybe even beneficial? Was the whole uproar over the
supposed plight of the manatee in fact just an environmentalist hoax to begin with? Or (to put a
more charitable face on it) is this a demonstration of the self-correcting nature of science in the
light of new data?
Before jumping to any of these conclusions, we should read more of what O'Shea and
Ackerman had to say: "Possible increases in manatee population size since the mid-1970's may
be attributable to intensified conservation. However, the threats to manatee survival and
habitat loss have accelerated and are expected to increase. A turning point may soon be
reached, if it has not already. This contention is supported by the possibility that upward
trends in counts at power plants in winter may have diminished in the late 1980's and early
1990's ...; by the lack of a notable increase of counts and a higher number of deaths in
southwestern Florida ...; by the high number of recovered carcasses in 1994 [plus a still higher
number in 1995 and a disastrous start to 1996 see other news in this issue]; and by increased
numbers of boats and the more complex technology of high-speed boating.... Because of the
lack of accuracy and precision in estimates of population size, the size of the Florida manatee
population could decrease even while counts may seem to increase or be stable.... Given that
negative effects on manatee populations will continue to increase with burgeoning human
populations in Florida and that decreases in adult mortality can result in growth and long-term
persistence of Florida manatee populations ..., no prudent alternatives exist to maintaining
proactive, vigorous management aimed at mortality reduction."
In short, the catch is that even if the manatee population has grown under the protection it
has received, we are rapidly approaching the limits of the protective measures now
envisioned. The legally-mandated Manatee Protection Plans are already in place in at least four
of the 13 Florida counties considered critical for manatee protection, and further tightening of
regulation beyond what is in these plans is likely to be strenuously opposed. Meanwhile, the
numbers of humans, boats, and new developments continue to grow without limit. An
aggressive manatee-protection campaign has bought the population valuable time, but the
onslaught of demography will soon throw the manatee and its allies back on the defensive,
facing ever-grimmer odds. The population recruitment suggested by the latest synoptic surveys
may still prove to have been no more than reinforcements thrown into a losing battle.
The shape of this battle is already evident to those who read the published evidence
more closely. O'Shea and Ackerman cite "data ... that suggest substantial population growth
from internal recruitment at the Crystal River and at Blue Spring and slower growth or
stability on the Atlantic Coast...." These preliminary results show, in other words, that
manatees have increased in precisely those areas where they are most strictly protected, but
may have been unable to do so where boating activity and boat-caused mortality are heaviest.
What we see here, in fact, is an inadvertent experiment to determine what level of human
harassment manatee populations can tolerate. The results neatly demonstrate both their ability
to flourish, given reasonable protection, and (more realistically) their likely inability to survive
much longer, as the worst that Florida is presently throwing at them worsens still further.
This was not, however, the message that was reaching the public in the wake of the
1996 synoptic surveys. As manatee researchers anticipated when the State of Florida began
these surveys several years ago, they are two-edged weapons. While it is always useful to have
minimum counts to plug into population models, the danger is that these minimum counts will
be taken as actual estimates of population size, and growth in these numbers will be
misinterpreted as actual growth in population. They are in fact being misinterpreted this way in
the Florida press, by boating advocates and others, and some have even begun to call for
downlisting of the Florida manatee to a less endangered status.
The issue of downlisting should, in principle, be easy to dismiss. The revised Florida
Manatee Recovery Plan (1996 version, due to be published in a few weeks) states that
"downlisting should be considered when ... the population is growing or stable, when
mortality factors are controlled at acceptable levels or are decreasing, and when critical
habitats are secure and threats to them are controlled or decreasing." Of these three criteria, it is
obvious that the latter two are not likely to be met in the foreseeable future: human-caused
mortality continues to rise, and the threats of human population growth and development
pressures are anything but "controlled or decreasing." In practice, however, only the first
criterion readily registers in the public consciousness, where higher manatee counts necessarily
mean a recovering population.
Sometimes, however, one problem is solved by another; and the misleading press
coverage of the January and February surveys was fortuitously swept from the headlines by the
disastrous manatee dieoff in March. For the moment, this antidote of well-founded alarm
seems to have taken effect, but spells of complacency are bound to recur. When they do and
whenever any of us has occasion to communicate with the public or the mass media on these
issues we need to emphasize as strongly as possible the following points:
1. The statewide synoptic surveys provide only minimum counts, not estimates of the total
population; they are extremely sensitive to weather conditions and cannot be compared
statistically with each other or with estimates derived from other techniques.
2. While it is possible that the total manatee population in Florida has increased, it is more
certain (and more significant) that increases have occurred in precisely those areas where
manatees are best protected, while in areas of lesser protection there has been little or no
increase (and none that is likely to be sustained).
3. We can take no comfort in any numerical increases that have been achieved, because the
protective measures that made them possible are approaching the limits of political
acceptability, while the threats to manatees only increase and can be expected to wipe
out the recent gains. For this reason, no talk of downlisting the Florida manatee is even
4. The manatee population is still small in absolute terms, and always vulnerable to
unexpected catastrophes like the March 1996 dieoff especially when, as in this case, the
victims are predominately adults in their prime, which are the animals most essential to
survival of the population. When some 2% of that population can be wiped out in one such
event over and above all other sources of mortality there is ample cause for concern about
the species' future.
Not all these points are easy to make in sound bites, but this is the message we urgently
need to get out. DPD
Jesse R. White, D.V.M.
Dr. Jesse White, well-known marine mammal veterinarian, died on 23 January 1996 at
his home in Dunnellon, Florida, at the age of 61 years. A native of Oklahoma, he received his D.
V.M. degree from Texas A&M University at College Station in 1962. He served as Staff
Veterinarian at the Miami Seaquarium, 1967-86, and Marine Mammal Veterinarian for the
Florida Department of Natural Resources, Homosassa, Florida, 1986-87. In 1984, he founded
the Florida Manatee Research and Education Foundation, an organization for which he always
served as Director and President. He was an Adjunct Professor at the College of Veterinary
Medicine, University of Florida, 1983-87, and Clinical Professor in the Department of Small
Animal Medicine at the same institution from 1987 until his death. He received several
lifetime achievement and conservation awards from professional associations, and was the first
veterinarian to serve on the U.S. Marine Mammal Commission's Committee of Scientific
Advisors. His publications focused on manatees and marine mammal care and maintenance.
He was particularly interested in captive breeding of manatees, and it was during his tenure at
the Miami Seaquarium that the first successful and regular breeding of captive Florida
manatees began. (John R. Twiss, Jr. and DPD)
SHOULD THE SIRENIA SPECIALIST GROUP ESTABLISH A HOME PAGE
ON THE WORLD WIDE WEB?
A couple of weeks ago, I attended a meeting of the IUCN Species Survival
Commission (SSC) Steering Committee which was held in Australia. I was invited to attend
the meeting as an observer along with other Specialist Group Chairs from the region. The
Australians enjoyed being the only delegates not suffering from jet lag, a reverse of the usual
The issue of communication among and within Specialist Groups was discussed. The
SSC is planning to set up a home page on the World Wide Web which will concentrate on
being a link among the home pages established and maintained by various Specialist Groups.
This initiative raises questions for the Sirenia Specialist Group:
How many members would have access to a Sirenia SSG home page on the World Wide
Web if one were established?
Is there anyone who is prepared to establish and maintain such a page?
The page would have many advantages. Here are a few:
It would be a source of up-to-date information on manatees and dugongs.
It would be an additional method of distributing this newsletter.
It could enable Group members to access the gray literature and publications lists of other
It could be an effective method of distributing the Dugong and Manatee Action Plans when
they are finalized.
I do not see a Sirenia Specialist Group home page duplicating the role of MARMAM.
Your reactions, please; and is there a volunteer who is willing to establish and maintain
the page? Helene Marsh
NIRS BREAKS THROUGH SIRENIAN FOLIAGE
The conventional methods used for analyzing nutrient contents of seagrasses are
laborious and expensive. This is essentially why most studies dealing with sirenian and/or
seagrass nutritional ecology have limited numbers of replications. This may now be a thing of
Near-infrared reflectance spectroscopy (NIRS) has been in use for the analysis of
agricultural and food products since the late 1960's. This technique makes use of a small
segment of the electromagnetic spectrum (just above the visible region, 700 nm to the edge of
the infrared region, 2500 nm), called near-infrared (NIR). The NIR spectrum contains
information on the major building blocks of the biological world (CH, OH, and NH groups).
I applied this technique in my research entitled "The ecology of seagrasses as food for
dugongs and green turtles" at James Cook University. It allowed me to predict multiple
constituents of seagrass relevant to a dugong's (and green turtle's) perspective, for a large
number of samples (ca. 1,200, which would have been expensive and laborious using
conventional methods). This technique allowed me to select the "best" (most typical)
calibration set (15-20% of the total), based on the population's spectral variability, for which
precise conventional nutritional/chemical analyses were performed. These calibration data
were then used for the development of predictive equations for each constituent using a cross-
validation technique. The predicted values have a good agreement with the laboratory values.
The r2 values for the different constituents were: 0.99 for nitrogen, 0.96 for organic matter,
0.94 for neutral detergent fiber, 0.91 for acid detergent fiber, 0.90 for lignin, 0.91 for water-
soluble carbohydrates, and 0.92 for in vitro dry matter digestibility.
NIRS analysis offers several advantages. It is rapid, nondestructive, and
environmentally safe. One of its most important features is that it can analyze samples for
multiple constituents. Even though this technique has existed for more than 20 years, it has
never been employed in nutritional ecology of wildlife. This technique will certainly simplify
the task of trying to understand why sirenians prefer certain species of foliage. Lem V.
COURSES ON ZOO ANIMAL BEHAVIOR AND WELFARE
Edinburgh Zoo, in conjunction with the University of Edinburgh, is again offering a
two-week summer school course from 15 to 26 July 1996 on Zoo Animal Behaviour and
Welfare. It is designed for all those involved in management and husbandry of captive animal
populations, and will update participants on the latest scientific theory and its practical
implementation. Registration deadline is 31 May 1996.
A new two-module short course on Assessment and Implementation of Animal Welfare
Programmes will also be offered on 1-3 November and 6-8 December 1996. (The first
weekend module will cover scientific assessment of animal welfare; the second, animal welfare
in practice.) Covering aspects of the new Royal College of Veterinary Surgeons' Certificate in
Animal Welfare, Ethics and Law, this course will introduce the current scientific methods that
are used to assess and understand animal welfare and demonstrate how these can be practically
For information on either course, contact Hamish Macandrew, UnivEd Technologies
Ltd., FREEPOST, 16 Buccleuch Place, Edinburgh EH8 OLL, UK; tel.: 0131-650-3475; fax:
Dugongs Take Years to Recover
From Seagrass Loss. Preen and Marsh
(1995) report dugong deaths associated with
the loss of some 1000 km2 of seagrass in
Hervey Bay, Queensland, Australia,
following a flood and two cyclones in 1992.
Aerial surveys have been used to track the
resultant changes in dugong numbers in
the region. The surveys suggest that the
decline had ceased by 1993:
Date Population Estimate
1988 2206 s.e. 420
1992 1109 s.e. 383
1993 579-629 s.e. 126
1994 807 s.e. 151
However, calf counts associated with
the surveys suggest that the population may
take even longer to recover than originally
Date % Calves
These figures parallel changes in the
pregnancy rate and proportion of
reproductively active males in Torres Strait
dugongs coincident with an extensive
seagrass dieback in that region in the mid-
1970's (Marsh 1995). Data from
Australia suggest that large-scale diebacks
of tropical seagrasses, often associated with
extreme weather events such as floods or
cyclones, are relatively common (Poiner
and Peterken, 1995). In addition to any
direct mortality of dugongs associated with
such diebacks, their impacts on the life
history of dugongs in the affected area is
likely to be serious and long-lasting. The
only data I know of concerning temporal
changes in the pregnancy rates of manatees
are from Marmontel (1995), who provides
evidence that suggests an increase in Florida
from 1976 to 1991.
Does anyone else have any data
suggesting temporal changes in the life
history parameters of sirenians?
Marmontel, M. 1995. Age and reproduction
in Florida manatees. In: T.J. O'Shea, B.
B. Ackerman, and H.F. Percival (eds.).
Population biology of the Florida manatee.
Information & Technology Report (U.S.
Dept. Interior, Natl. Biological Service) 1: 98-
Marsh, H. 1995. The life history, pattern of
breeding, and population dynamics of the
dugong. In: T.J. O'Shea, B.B. Ackerman,
and H.F. Percival (eds.). Population
biology of the Florida manatee.
Information & Technology Report (U.S.
Dept. Interior, Natl. Biological Service) 1:
Poiner, I.R., and C. Peterken. 1995.
Seagrasses. In: L.P. Zann and P. Kailola
(eds.). The state of the marine environment
report for Australia. Technical Annexe:
1. The marine environment. Canberra,
Australia, Dept. of Environment, Sport and
Preen, A., and H. Marsh. 1995. Response of
dugongs to large-scale loss of seagrass
from Hervey Bay, Queensland, Australia.
Wildlife Research 22: 507-519.
- Helene Marsh
Manatee Plans and Materials Being
Developed. The regional management plan
for the West Indian Manatee in the Wider
Caribbean was approved at the Third Meeting
of the Interim Scientific and Technical
Advisory Committee to the Protocol
Concerning Specially Protected Areas and
Wildlife (SPAW) in the Wider Caribbean
Region (Kingston, Jamaica, 11-13 October
1995). The plan will be published in
English, French, and Spanish.
The Caribbean Environment
Programme is also supporting the preparation
of manatee recovery plans in Belize,
Colombia, Honduras, Mexico, Suriname,
Trinidad and Tobago, and Venezuela, and
the development of educational activities on
manatee conservation in Belize, Jamaica,
Mexico, and Suriname. It is also
producing a number of educational
materials for children in English, Spanish,
and French on manatee conservation as part
of a region-wide public awareness and
education campaign. A number of these
products (poster, coloring book, and bumper
stickers) are available, as is a directory of
manatee experts and institutions from the
Wider Caribbean including Brazil. Address:
Regional Coordination Unit for the Caribbean
Environment Programme, 14-20 Port Royal
Street, Kingston, Jamaica; tel.: 1-809-922-
9267/9268/9269; fax: 1-809-922-9292. -
(Source: The Pilot [UNEP], No. 13.)
Major Manatee Dieoff in
Southwest Florida. Beginning 5 March
1996, fresh manatee carcasses began turning
up in southwest Florida between
Englewood and Marco Island. The animals
were large adults, and the only gross
abnormality was a diffuse bilateral
pneumonia. By 10 March, as many as four
carcasses were being reported per day. By
the 13th there were reports of 11 deaths in
one day, and the Florida Department of
Environmental Protection's (DEP) Marine
Mammal Pathobiology Laboratory in St.
Petersburg, which was handling the
necropsies, moved its operation to a field
station on Sanibel Island to process the
carcasses more efficiently. As of 4 April,
the total number of carcasses reported in the
area since 5 March amounted to 110, with
the total continuing to mount as this went
to press. Even if a few of these turn out to
have died from causes other than that of the
majority, this will still easily rank as by
far the largest single mass mortality of West
Indian manatees in recorded history.
All of the carcasses so far necropsied
were in good flesh; none had any indication
of cold stress and all had pulmonary lesions
characterized as diffuse, bilateral
discoloration of purple and bright red on
the serosal surface of the lungs. On a cut
surface, the lungs were congested and bled.
In the more severe cases, the primary
airways were filled with a serosanguinous
exudate that was adherent and occluded the
secondary airways. In the less severe cases,
the airways were open, but the pulmonary
parenchyma appeared the same in all cases
and there was a conspicuous absence of
inflammation. All other organs appeared
grossly normal. Death was rapid and the
result of pulmonary failure.
The vast majority of animals were
large (275 cm or more); the smallest were
191 cm and there were no perinatal-sized
animals involved. At least seven animals
were pregnant. Tunicates were not observed
in any of the GI tracts. Microbiological
results indicated a diversity of bacteria that,
in the absence of an inflammatory response
and of consistency between cases, were
considered secondary to the event.
Following the guidelines of the
Marine Mammal Protection Act, the Florida
DEP has requested technical advice from the
Working Group for Unusual Marine Mammal
Mortality Events. In addition to State
biologists, Federal scientists from the U.S.
Fish and Wildlife Service, National
Biological Service, National Marine
Fisheries Service, and Armed Forces
Institute of Pathology are cooperating in the
response to the dieoff, as well as scientists
from the University of Florida, University
of Miami, Miami Seaquarium, Sea World,
and Erasmus University in The Netherlands.
In 1995, Florida reported a total of
201 manatee deaths. This year, 200 have
died in Florida's waterways in little more
than three months.
The same area of southwest Florida
was the scene of another mass mortality in
1982 in which some 37 manatees died. These
deaths were traced to ingestion of tunicates
that contained red-tide organisms. That
outbreak included cases of manatees
behaving abnormally, and some animals
recovered; but in this case there have been no
reports of sick or strangely-acting manatees,
only deaths. Although the 1996 incident
has coincided with a red tide that has killed
sea birds and other marine animals,
preliminary screening of manatee blood for
red-tide toxins has been negative. Neither
have any of the other analyses so far
produced any conclusive evidence of a
On 1 April, researchers captured
six manatees in the area of the dieoff and
extracted blood from them in an attempt
to obtain a control group of live animals
with which to compare analytical findings
from the carcasses. For instance, if the live
animals have been exposed to the disease,
they might show unusual blood cell
counts or perhaps antibodies. Alternatively,
whatever is causing the disease may be
present in the control group's blood but
for some reason absent from the blood of
the animals that have died. Passive
Integrated Transponder (PIT) tags were also
placed in the captured animals, so if any of
them turn up dead in the near future, they
could provide insight into the incubation
period if an infectious disease is to blame,
or possibly give other clues about the
cause of death. At this time a viral infection
is considered a likely culprit, but unusual
bacteria and natural or man-made toxins
have not been ruled out. (Source: Florida
Award and New Job for Pat Rose. -
Patrick M. Rose, who has headed the Florida
Department of Environmental Protection's
(DEP) manatee program for the past twelve
years, was recently the recipient of a 1995
special edition National Conservation
Achievement Award sponsored by the
National Wildlife Federation (NWF).
This award recognizes contributions
made by dedicated public servants in the
cause of conservation. Recipients are selected
by the Awards Committee of the NWF Board
Pat has long been known for his
aggressive championing of boat speed zones
and other protective regulations on behalf of
the Florida manatee, and has borne the brunt
of many hard-fought intra-agency political
battles, as well as much bitter public criticism
incurred in the course of regulatory
controversies. To him belongs much of the
credit for the great success DEP has had to
date in enacting manatee protection.
Pat instituted the Florida Audubon
Society's manatee program, then became the
U.S. Fish and Wildlife Service's first
Manatee Coordinator, before starting DEP's
manatee program. He is also a noted
manatee photographer, and his still and
motion pictures have appeared in many
publications and films.
In recent weeks he has left DEP to
become the new Director of Government
Relations for the Save the Manatee Club,
which has opened a new satellite office in
Tallahassee in order to become more
involved in advocacy for stronger
manatee protection. Pat's dedication and
government experience will be major assets
to this effort, and his many friends and
colleagues are happy that his talents will not
be lost to the cause of manatee
conservation. (Sources: DEP, Save the
Manatee Club Newsletter)
Save the Manatee Club Goes
Online. Visit the Save the Manatee Club's
new web site! Facts about manatees,
information about the Adopt-A-Manatee
program (including an online adoption
application), and materials for educators are
all featured. Address: http://objectlinks.com/
More on Manatee Breeding in
Nuremberg. A letter to the U.S. Marine
Mammal Commission from Dr. Peter
Miihling, Director, Tiergarten Nmrnberg,
supplements the information reported in
Sirenews No. 22. He reports that between
1981 and 1995, 14 manatees in two
generations were born at his zoo, including
two births of twins. The founding stock
came from Guyana.
The manatee pool is 1.6 m deep with a
surface area of some 50 m2 (not including an
island). The manatees often rest in the
shallow areas, while ducks in the enclosure
rest in turn on the manatees' exposed backs.
No behavioral problems have been
observed, even with up to ten manatees in the
pool at once. As of June 1995, only four
animals were still held, the others having
been transferred to the Arnheim Zoo,
Tierpark Berlin, Singapore Zoo, and
Seapalace in Japan. Plans are now underway
to enlarge the manatee pool and make more
room for continued breeding.
Cultivation Grazing by Dusongs in
the Moluccas. From 1990 to 1995 we
studied the interactions between seagrasses
and dugongs in the Moluccas, East Indonesia.
This project was a collaboration between the
Pattimura University at Ambon, LIPI
Jakarta/Ambon and The Centre for
Environmental Science of Leyden
University, The Netherlands. We found
convincing evidence that dugongs practice
Preen (1993) postulated that seasonal
nutritional stress in subtropical areas, and a
response to this stress by "cultivation
grazing," would be major factors in the
observed difference in dugong herd size
between tropical and subtropical areas.
An impact of environmental stress on
herd size has also been observed for
terrestrial herbivores. Increased densities of
African elephants caused by restriction in
available habitat led to an increase in
group size (Laws, 1975). According to
Preen (1993, 1995), "cultivation" grazing
occurs when herds of dugongs forage
intensively in an area, effecting a high
level of seagrass removal over a large area.
"'Cultivation' grazing allows dugongs to
improve the quality of their diet by one or
more of the following: (1) maintaining the
meadow at a younger, actively growing
stage, so the seagrasses contain less fiber;
(2) converting the meadow to a lower seral
stage composed of preferred and nutritionally
superior seagrasses; and (3) concentrating
the regrowth vegetation into areas that
can be efficiently cropped. The nutritional
benefits of these modifications to the
seagrass meadows would maximize the
fitness of individual dugongs." McNaughton
(1979) postulated that the fitness benefits
gained by individual animals through
increased foraging efficiency could lead to
the development of herding behavior in
ungulates. According to Preen (1993, 1995),
due to their mode of feeding, these benefits
could only be achieved if the dugongs fed in
Preen (1993, 1995) also stated that in
tropical areas, the benefits of cultivation
grazing may not be necessary, or relevant, in
which case there may be no pressure to feed
in large herds.
The conclusions of Preen (1993,
1995) are contradicted by the findings of our
study, since we observed concentrated
feeding plots inside both intertidal and
subtidal seagrass meadows in the Lease
Islands, caused by cultivation grazing
practice by small herds of dugongs (2-6
animals). These small herds could
sufficiently disturb the seagrass bed,
through a dense grazing pattern, to
maintain monospecific meadows (Halodule
uninervis and Halophila ovalis) of low
The principal effect of cultivation
grazing in an intertidal multispecies meadow
in our study area (Nang) was the creation of
monospecific Halodule uninervis pioneer
meadows surrounded by multispecies
associations. This pattern of grazing,
similar to patterns described for Moreton
Bay by Preen (1993, 1995), leads to the
spatial containment of less favored species,
like (in our study) Thalassia hemprichii and
The principal effect of cultivation
grazing in a subtidal monospecific Halodule
meadow in our study (Haruku) was a higher
in vitro digestibility inside the grazing plots,
compared with the undisturbed meadow. This
phenomenon has not been described by Preen
(1993, 1995) for Moreton Bay. Cultivation
grazing in monospecific meadows results in
patches with lower standing crop, but with a
higher in vitro digestibility, indicating a
feeding strategy along a productivity gradient
as described by Van der Koppel et al. (1995).
During our study we have identified
at least five permanent feeding plots with
concentrated, regular patterns of recropping
by dugongs. We concluded that dugongs in
these plots grazed in facultative feeding
assemblages with loose social interaction
rather than in fixed herds with strong social
bonds. Cultivation grazing benefits all
individual dugongs through an increased
rate of digestibility and energy intake, but
lowers the amount per bite and overall
biomass in the grazing plots.
With a computer model we calculated
the maximum sustained population size for
Haruku Strait as 11 dugongs. With a
maximum sustained number of 90 dugongs
and the estimated minimum population of
22-37 dugongs for the study area, the
quantity of the available seagrass in
combination with mortality from accidental
capture by man may be major factors
determining population size, but seagrass
quality seems to determine herd size and
A "cultivation" effect similar to that
observed for small groups of dugongs in the
present study has been observed for small
herds of manatees in Florida (Lefebvre and
Powell, 1990). Florida manatees, with
muzzles less specialized for bottom feeding,
do not produce feeding trails in the manner
of dugongs. Instead, when they feed on
seagrasses, they crop circular patches (mean
27 m2). Interestingly, there is some evidence
that they return to the same patches in
Our study confirms that the practice
of recropping permanent grazing plots
through cultivation grazing is moreover part
of a permanent evolutionary pattern of
adaptations of the dugong as a species in
response to its low-quality forage, rather than
a temporary response to seasonal nutritional
stress as postulated by Preen (1993, 1995).
Laws, R.M. 1975. Elephants and their
habitats. Oxford, Clarendon Press: 1-376.
McNaughton, S.J. 1979. Grazing as an
optimization process: grass-ungulate
relationship in the Serengeti. Amer. Nat. 113
Preen, A. 1993. Interactions between
dugongs and seagrasses in a subtropical
environment. Ph.D. thesis, Dept. of
Zoology, James Cook Univ., Australia: 1-
Preen, A. 1995. Impacts of dugong foraging
on seagrass habitats: observational and
experimental evidence for cultivation
grazing. Marine Ecology Progress Series
Van der Koppel, J., J. Huisman, R. Van der
Wal, and M. Olff. 1995. Patterns of
herbivory along a gradient of primary
productivity: an empirical and theoretical
investigation. Ecology (in press).
- Hans De longh (Centre for
Environmental Science, Leiden University,
[EDITOR'S NOTE: I strongly
suspect that production of feeding trails is a
function of seagrass and substrate type and
density, not of degree of muzzle
specialization. If seagrasses are sparse,
delicate, and easy to uproot, a sirenian
can maintain headway while removing
most of the biomass, thereby producing a
trail during a single dive. If the foliage is
thicker and/or the rhizomes are harder to
dig out, only a small patch can be cleared
during a single feeding bout (dive), and
there is no reason for patches cleared on
successive dives to be linearly aligned, so a
large circular feeding scar results. If
manatees were observed feeding on (e.g.)
sparse Halophila beds, they might be found to
make trails too!]
PREEN RESPONDS: It is very
pleasing that cultivation grazing has been
documented from a tropical area, and that the
process seems identical to that in subtropical
Moreton Bay, where I did my study. The
only substantive differences appear to be the
size of the dugong herds and the size of the
cultivation patches. In Moreton Bay the
median herd size was 140, and cultivated
areas were up to 75 ha within 11,054 ha of
seagrass. In Hans De Iongh's study, the
herds were 2-6 dugongs and the study area
(Nang Bay) was 6 ha.
Hans has misunderstood the nature of
cultivation grazing in Moreton Bay. It is not
"a temporary response to seasonal nutritional
stress." Rather, I speculated that seasonal
stress may necessitate cultivation grazing
(and omnivory; Preen, 1995, Jour. Mamm.
76:163-171) by dugongs whenthey live at
the extremities of their range. However, this
is not to suggest that cultivation grazing (or
omnivory) are seasonal in Moreton Bay, as
they are not, or to imply that cultivation
grazing could not occur in more tropical
areas. Indeed, in the Gulf of Carpentaria, in
northern Australia (15.5 S), I have
subsequently found that large herds of
dugongs persistently feed in the same
locations for extended periods, and that
they appear to return to these areas,
perhaps on an annual cycle.
Interestingly, in this area that is
overwhelmingly dominated by an abundance
of dense Syringodium isoetifolium, the
dugongs feed more in the manner described
for manatees. Rather than forming feeding
trails, they tend to form small oval feeding
patches (ca. 30 x 50 cm) from which they
remove only the leaves. These patches grow
and coalesce, and eventually very large areas
are substantially denuded. It is only after
most of the shoots have been removed that
they start removing substantial amounts of
rhizomes. The extent to which this grazing
favors species like Halophila ovalis and
Halodule uninervis depends on the extent to
which the rhizomes of Syringodium are
removed. Mere cropping of the leaves results
in a rapid and vigorous shooting by the
Syringodium. Tony Preen
The World's Most Primitive
Seacow. With support from the
National Geographic Society, I have been
working in Jamaica for the last three
years, collecting fossils of Prorastomus, the
oldest and most primitive sirenian known.
A site in the hills south of Montego Bay,
originally discovered by Roger Portell of the
Florida Museum of Natural History, is
yielding abundant postcranial bones of this
Early to Middle Eocene animal, which was
previously known almost entirely from a
single skull found at another Jamaican site in
the 1850's. Assisting Portell and myself in
the field are Steve Donovan of the
University of the West Indies, Kingston,
Jamaica, and Kevin Schindler of the Lowell
Observatory, Flagstaff, Arizona. The new
material may represent a new species distinct
from the type species P. sirenoides.
In addition to numerous ribs (which
are typically sirenian in their bulk and
density) and vertebrae, we have found a
scapula, two humeri, an ulna, several pelvic
bones, three femora, a tibia, a metapodial, a
phalanx, and several skull elements and
teeth. Much of the material collected
remains to be prepared, and probably
includes still other parts of the skeleton.
The appendicular bones of these
pig-sized, 50-million-year-old seacows
resemble those of land mammals far more
than do bones of Protosiren, the next most
primitive seacow known. Since even
Protosiren retained well-developed hind
limbs and was obviously amphibious, it
seems that prorastomids were even more
capable of terrestrial locomotion, although
their aquatic adaptations (retracted nasal
opening, dense ribs) indicate that most of
their time was spent in the water. They still
possessed two or more sacral vertebrae that
were connected to the pelvis, but these
vertebrae were not fused to each other,
indicating a degree of spinal flexibility
comparable to that of early whales like
Rodhocetus. Prorastomids also seem to lack
an enlarged tail like that of later sirenians, so
they may have used the hind limbs to swim,
like the primitive whale Ambulocetus.
Further fieldwork is planned, and
as collecting and preparation proceed, we
expect to rapidly learn more about the
anatomy and lifestyle of this true "missing
link" between land mammals and sirenians.
Manatee Rescue in Chiapas. One
of the most important areas for manatees in
Mexico is the Usumacinta River and its
basin, with streams and many lakes, in the
states of Chiapas and Tabasco. The number
of manatees in this area has not been
estimated, but it appears they are fairly
During the first months of 1995, the
southeastern states of Mexico suffered an
extensive drought; the water levels of many
streams and lakes decreased to critical levels.
On 29 May we received news of a group of
manatees isolated in an almost dry lake
named San Juan (1746'44" N, 91055'45"
W), located in the municipality of Catazaja in
Chiapas. Manatees have been sighted in this
lake for more than 10 years.
In March and April, the people from
villages nearby took grass to the water to
feed the manatees, because they realized that
the water level in the lake was dropping fast,
and the manatees had nothing to eat. By late
May, authorities of Chiapas decided to rescue
The rescue work lasted from 31 May
to 4 June. Seventeen manatees were captured
and moved. From the second day of capture
we collected data on morphology and sex,
and also took five samples of blood and eight
of skin for genetic analysis.
The animals were corralled with a
100-m-long fishing net and then caught by
hand by slipping a rope around their
peduncles while the net was contracted
slowly. They showed an extraordinary
ability to escape from the net by lifting the
lower edge with their noses. During
transport, which lasted about 30 min, all
animals showed passive behavior until they
were successfully released.
The authorities decided to free the
rescued manatees in the Catazaja Lake, which
has a maximum area of 16,000 ha in the
rainy season, and where the local fishermen
estimate a population of 50-80 manatees.
Of the 17 captured manatees, five
were adults and the rest were juveniles,
including at least one calf. The sexed animals
were seven females and four males.
The Chiapas state authorities are now
planning to initiate an educational and
research program in the region with the aid
of the Quintana Roo Research Center, where
a research program on the Antillean
manatee was started in 1987.
A video of this rescue is available (8
minutes long, VHS). For information, fax:
983-20447 in Chetumal, Mexico. -
Benjamin Morales Vela and David
Olivera G6mez (El Colegio de la
Frontera Sur [ECOSUR], Apdo. Postal 424,
C.P. 77000, Chetumal, Q. Roo, Mexico)
New Dugong Studies. Jean-
Philippe Das has been conducting studies of
dugongs in New Caledonia, and in October
1995 he produced a wide-ranging 97-page
privately-printed report entitled Etude des
dugongs en Province-Nord: Compte-rendu.
It covers the distribution, ecology, and status
of dugongs in the province, giving data
from aerial and interview surveys, catch
data, and ethnobiological information. In
1994 he produced another report, Etude des
dugongs en Province-Sud. He can be
contacted at: 18 Rue Rameau, 91160
Longjumeau, France (tel./fax: 33-90-49-55-
28) or at CEMMEN Conservation et
Etude des Mammiferes Marins en
Nouvelle-Caledonie, BP 13098, 98800
Noum6a, New Caledonia (tel./fax: 687-44-
Symposium on Cetaceans and
Dugongs. A Symposium and Workshop on
the Biology and Conservation of Small
Cetaceans and Dugongs of Southeast Asia
was held in Dumaguete, Negros Oriental, on
26-30 June 1995 and hosted by the Silliman
University Marine Laboratory. The one-day
Symposium was attended by over 120
participants from 10 countries.
The group agreed that its work should
include the dugong, since it faces many of
the same threats as small cetaceans and
because in several nations dugongs and small
cetaceans are studied by many of the same
The Workshop agreed to establish a
small cetacean interest group in Southeast
Asia, with a regional newsletter appearing at
least three times a year (to be published by
the Ocean Park Conservation Foundation).
The proceedings of the Workshop are being
edited by Dr. W. F. Perrin and will be
published as a UNEP East Asian
Technical Series Report. (source: The Pilot
[UNEP], No. 13.)
U.S. Postage Stamp to Feature
Manatee. For the first time, a manatee is to
appear on a United States postage stamp. Part
of a sheet of 15 multicolored stamps
featuring 15 different endangered species,
the 32-cent stamp depicting a Florida
manatee is scheduled for its first day of
issue on 2 October 1996 in San Diego,
The U.S. is late in joining the club
of nations that have put sirenians on
their stamps: at least 31 other countries
have already done so. The first were
apparently Niger and Cameroon in 1962. Still
conspicuously absent from the list is
Australia. How about it down there?? It's a
cheap and easy way for a government to
help raise consciousness about sirenians
among children and other collectors the
world over. DPD
Publication of Sirenian Bibliography
Still Approaching! After further delays
caused by the past winter's government
furloughs and shutdowns (what else can go
wrong?), Domning's Bibliography and
Index of the Sirenia and Desmostylia is
now expected to appear this summer as
Number 80 in the series Smithsonian
Contributions to Paleobiology. It will
consist of a single sewn, paperbound
volume (about 8" x 10" format) of over 610
pages. It is an exhaustive, annotated and
indexed compilation of 500 years of scientific
and popular literature on the biology,
paleobiology, and ethnobiology of sirenians
and desmostylians. Since the Smithsonian
does not retail its series publications to the
general public, arrangements have been
made for the Save the Manatee Club to
obtain a limited supply of copies for sale to
individuals. The retail price has been
tentatively set at around US$25.00 per
copy. If you wish to acquire a copy for
personal use, please contact the Save the
Manatee Club, 500 N. Maitland Ave.,
Maitland, Florida 32751, USA (phone: 1-
800-432-5646), as soon as possible to
reserve a copy and obtain up-to-date
information on price and handling costs. To
repeat, copies are not available for shipment
at this time, but will be ready sometime
in the next months. DPD
The following abstracts are of papers and posters presented at the Eleventh Biennial
Conference on the Biology of Marine Mammals, held at Orlando, Florida, 14-18 December
Anderson, P.K., and R.M.R. Barclay. 1995. Acoustic signals of solitary dugongs:
physical characteristics and behavioral correlates. Jour. Mamm. 76(4): 1226-1237.
Bizzarini, F. 1994. Osservazioni sull'Halitherium schinzi Kaup, 1838 (Sirenia,
Mammalia) conservato press il Museo Civico di Storia Naturale di Venezia. Boll. Mus.
Civ. Stor. Nat. Venezia 43: 163-171. [In Italian; Engl. summ.]
Brownell, R.L., Jr., K. Ralls, and W.E. Perrin. 1995. Marine mammal biodiversity:
three diverse orders encompass 119 species. Oceanus 38(2): 30-33.
Cashman, M.E., T.L. Ness, W.B. Roess, W.G. Bradley, and J.E. Reynolds III. 1996.
Isolation and characterization of a cDNA encoding interleukin 2 from the Florida
manatee, Trichechus manatus latirostris. Mar. Mamm. Sci. 12(1): 89-98.
De Iongh, H.H., B.J. Wenno, B. Bierhuizen, and B. Van Orden. 1995. Aerial survey of
the dugong (Dugong dugon MUller, 1776) in coastal waters of the Lease Islands, East
Indonesia. Mar. Freshwater Res. 46(4): 759-761.
Domning, D.P., S.K. Donovan, H.L. Dixon, R.W. Portell, and K. Schindler. 1995.
The world's most primitive seacow: a new sirenian site in western Jamaica.
[Abstract] Geol. Soc. Amer. Abstrs. With Progs. 27(6): A386.
Domning, D.P., and H. Furusawa. 1995. Summary of taxa and distribution of Sirenia in
the North Pacific Ocean. The IslandArc 3(4): 506-512.
Duignan, P.J., C. House, M.T. Walsh, T. Campbell, G.D. Bossart, N. Duffy, P.J.
Fernandes, B.K. Rima, S. Wright, and J.R. Geraci. 1995. Morbillivirus infection in
manatees. Mar. Mamm. Sci. 11(4): 441-451.
Gingerich, P.D., M. Arif, M.A. Bhatti, H.A. Raza, and S.M. Raza. 1995. Protosiren
and Babiacetus (Mammalia, Sirenia and Cetacea) from the Middle Eocene
Drazinda Formation, Sulaiman Range, Punjab (Pakistan). Contr. Mus. Pal. Univ.
Michigan 29(12): 331-357. [Protosiren sattaensis, new species]
Hasegawa, Y., T. Muramatsu, and Y. Miyazawa. 1995. A desmostylian tooth from
the Tomikusa Group, Nagano Prefecture. Sci. Repts. Yokohama Natl. Univ., Sec. II, Biol.
& Geol. No. 41/42: 1-11. [In Japanese; Engl. summ.]
Hasegawa, Y., Y. Taketani, H. Taru, 0. Sakamoto, and M. Manabe. 1995. On
sexual dimorphism in Paleoparadoxia tabatai. The Island Arc 3(4): 513-521.
Heizmann, E.P.J. 1992. Das Tertiar in Sudwestdeutschland. Stuttgart Beitr. Naturk., Ser.
C: Allg. Aufsdtze 33: 1-61. [Mentions Halitherium.]
Inuzuka, N., D.P. Domning, and C.E. Ray. Summary of taxa and morphological
adaptations of the Desmostylia. The Island Arc 3(4): 522-537.
Kamiya, T. 1994. [Steller's sea cow.] Toba Super Aquarium No. 12: 14-15. [In Japanese.]
Kataoka, T. 1987. "Sirenology" [general biology of the dugong]. Jour. Mie Prefecture
Zool. Soc. No. 9: 3-7. [In Japanese.]
Kataoka, T., T. Mori, Y. Wakai, J.A.M. Palma, A.A.S.P. Yaptinchay, R.R. de Veyra,
and R.B. Trono. 1995. Dugongs Dugong dugon (Muller, 1776) of the Philippines: A
report of the joint dugong research and conservation program. Pawikan Conservation
Project, Philippines, and Toba Aquarium, Japan: 1-168.
Kettembeil, S. 1995. Dugong vom Aussterben bedroht. Naturwiss. Rundschau 48(1): 29.
Kimura, M., H. Furusawa, T. Sagayama, Y. Igarashi, A. Suzuki, and H. Fukusawa.
1995. Geologic age and paleoenvironment of fossil sirenian-bearing deposits
(Kinkomanai Formation) in the Shosambetsu region of northern Hokkaido, Japan. Jour.
Geol. Soc. Japan 101(5): 345-352. [In Japanese; Engl. summ.]
Kobayashi, S., H. Horikawa, and S. Miyazaki. 1995. A new species of Sirenia
(Mammalia: Hydrodamalinae) from the Shiotsubo Formation in Takasato, Aizu,
Fukushima Prefecture, Japan. Jour. Vert. Pal. 15(4): 815-829. [Dusisiren takasatensis, n.
sp.; Late Miocene]
Kraus, J. 1995. Florida manatee soft release. Endangered Species Tech. Bull. (U.S. Fish
& Wildl. Serv.) 20(5): 8-9.
Lockett, J. 1996. Dugongs dine with the herd. BBC Wildlife 14(1): 20-21. [Popular
account of cultivation grazing, based on Preen, 1995.]
Marmontel, M., T.J. O'Shea, H.I. Kochman, and S.R. Humphrey. 1996. Age
determination in manatees using growth-layer-group counts in bone. Mar. Mamm. Sci. 12
O'Shea, T.J., B.B. Ackerman, and H.F. Percival (eds.). 1995. Population biology of
the Florida manatee. Information & Technology Report (U.S. Dept. Interior, Natl.
Biological Service) 1: vi + 289. [Comprises 18 articles resulting from the workshop on
manatee population biology held at the University of Florida in 1992.]
Papastavrou, V. 1995. Gentle giant's furry fate: why the Steller's sea cow died out.
BBC Wildlife 13(11): 26.
Pirika Sirenia Research Group. 1992. Report on excavation of sirenian fossil from
Pirika Imakane, southwestern Hokkaido. Imakane (Japan), Imakane Township
Board of Education: [vi] + 133. [In Japanese; Engl. summ. Concerns a Pleistocene
skeleton of Hydrodamalis sp.]
Preen, A.R. 1995. Impacts of dugong foraging on seagrass habitats: observational
and experimental evidence for cultivation grazing. Mar. Ecol. Prog. Ser. 124: 201-213.
Preen, A.R., and H. Marsh. 1995. Response of dugongs to large-scale loss of seagrass
from Hervey Bay, Queensland, Australia. Wildl. Res. 22: 507-519.
Schindler, T., and K. Schindler. 1992. Ein Fund von Saugerzahnen im Oberen
Meeressand (Rupelium, Oligozan) von Bad Kreuznach (Mainzer Becken, SW-
Deutschland) mit Anmerkungen zum Aufschluss und zum sonstigen Fossilinhalt. Mainzer
Geowiss. Mitt. 21: 35-40. [Engl. summ.; mentions Halitherium schinzii.]
Schiro, A., and D. Fertl. 1995. Mermaids sighted in Galveston Bay. Soundings
(Galveston Bay Foundation) 7(3): 4-5. [Sightings of West Indian manatees in Texas.]
Schuhmann, H.-J. 1995. Der Manati, Trichechus senegalensis, im Rio Geba, Guinea-
Bissau. Natur und Museum (Frankfurt a. M.) 125(12): 402-409.
Schwartz, F.J. 1995. Florida manatees, Trichechus manatus (Sirenia: Trichechidae) in
North Carolina 1919-1994. Brimleyana No. 22: 53-60.
Takamura, N., and R. Sakai. 1994. [Stars of the Toba Aquarium: dugong.] Toba
Super Aquarium No. 12: 10-13. [In Japanese.]
Wallace, R.L. 1994. The Florida manatee: organizational learning and a model for
improving recovery programs. In: T.W. Clark, R.P. Reading, & A. Clarke (eds.),
Endangered species recovery: finding the lessons, improving the process. Covelo
(Calif.), Island Press: 131-155.
CHANGES OF ADDRESS
Benjamin Morales Vela, ECOSUR, Apdo. Postal 424, Chetumal, Quintana Roo
77000, MEXICO (fax: 983-20447)
Leslee Parr, Dept. of Biology, Portland State University, P.O. Box 751, Portland,
Oregon 97207, USA
Patrick M. Rose, 2545 Blair Stone Pines Dr., Tallahassee, Florida 32301
Essam Samson, Forest Engineer, P. 0. Box 11287, Yaounde, CAMEROON
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