Title Page
 Study area
 Materials and methods
 Results and discussion
 Conclusions and recommendation...
 Literature cited

Group Title: Technical report - Florida Cooperative Fish and Wildlife Research Unit - no. 39
Title: An evaluation of manatee distribution patterns in response to public use activities in Kings Bay, Crystal River, Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00073756/00001
 Material Information
Title: An evaluation of manatee distribution patterns in response to public use activities in Kings Bay, Crystal River, Florida
Series Title: Technical report
Physical Description: 35, 14 leaves : ill., maps ; 28 cm.
Language: English
Creator: Buckingham, Cheryl A
Publisher: Florida Cooperative Fish & Wildlife Research Unit, University of Florida
Place of Publication: Gainesville
Publication Date: 1990
Subject: Manatees -- Florida -- Crystal River   ( lcsh )
West Indian manatee -- Florida -- Crystal River   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (leaves 33-35).
Statement of Responsibility: Cheryl A. Buckingham.
General Note: "22 June 1990."
General Note: "Supported by: U.S. Department of the Interior, Fish and Wildlife Service, Cooperative agreement no. 14-16-00091544, RWO #52."
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Sea Grant technical series, the Florida Geological Survey series, the Coastal Engineering Department series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00073756
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 001894736
oclc - 29860775
notis - AJX0001


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Table of Contents
    Title Page
        Title page
        Page 1
        Page 2
        Page 3
    Study area
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
    Materials and methods
        Page 10
        Page 11
        Page 12
        Page 13
    Results and discussion
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
    Conclusions and recommendations
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
    Literature cited
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
Full Text



Cheryl A. Buckingham

Florida Cooperative Fish and Wildlife Research Unit
117 Newins-Ziegler Hall
School of Forest Resources and Conservation
Institute of Food and Agricultural Sciences
University of Florida, Gainesville, FL 32611


Chassahowitzka National Wildlife Refuge
7798 South Suncoast Blvd.
Homosassa, FL 32646

Supported by:

U. S. Department of the Interior
Fish and Wildlife Service
Cooperative Agreement No. 14-16-00091544
RWO #52

22 June 1990

This paper is to be cited as Buckingham, Cheryl A. 1990. An evaluation of manatee distribution
patterns in response to public use activities in Kings Bay, Crystal River, Florida. Florida Cooperative
Fish & Wildlife Research Unit, University of Florida, Gainesville. 49 pp.


Manatees are tropical and subtropical aquatic mammals that

belong to the order Sirenia. Worldwide, there are three species

of manatees, the West Indian (Trichechus manatus), the Amazonian

(T. inunquis) and the West African (T. senegalensis). A related

Sirenian genus, the dugong (Dugong duQon) inhabits the waters of

Australia and the Indo-Pacific Ocean. The Steller's sea cow

(Hydrodamalis gigas), a large Sirenian which occurred in the Bering

Sea, was hunted to extinction by the year 1766, only 25 years after

its discovery ((Packard et al., 1984). Throughout their history,

manatees have been hunted by humans for their meat and their dense

ivory-like bones. Today they are considered either rare or

endangered throughout most of their range. In most parts of the

world, human danger to manatees comes from accidental entanglement

in fishing nets or from subsistence hunters who intentionally trap

or harpoon the animals (Lefebvre et al., 1989). In the United

States, however, the greatest dangers come from boats, which each

year inflict injury and death on a significant number of animals.

Speed boats strike them at high speed, sometimes killing them by

impact or propeller wounds. Barges strike them or crush them

against the bottom. Manatees in the U.S. are also crushed in

locks, tangled in or swallow fishing lines and occasionally are

butchered (Brownell, 1980; 1981). They also may ingest chemicals

from urban runoff and aquatic weed control (O'Shea, et al., 1984).

In recent years a more subtle hazard has emerged. Boaters,

divers and snorkelers have learned that manatees can be easily


approached in their winter ranges. The growing popularity of

manatee encounters has led to an increase in the density of people

boating, diving and snorkeling in some areas. In one area, Kings

Bay, Crystal River, in Citrus County, Florida, there has been

growing concern that the welfare of manatees is being adversely

affected by the level of waterborne activities.

Nationwide publicity about the manatee has increased awareness

of its plight, but also has attracted an increasing number of

people to Crystal River each winter to see and interact with the

endangered animals. Most of these visitors rent boats and many

rent SCUBA or snorkeling gear. Nearly all manatee seekers center

their activities in the southern end of Kings Bay, near King's

Spring, the largest spring in the bay. It is there that the

greatest number of manatees can usually be found. The manatees in

the South Bay are seeking the warmth of the springs. Residents,

visitors, biologists and managers have become increasingly

concerned that high-density human water-related activities (mostly

boating, diving and snorkeling) in this area may be negatively

affecting the normal behavioral patterns of the manatees. Manatees

have been observed to dive or turn when approached by a motorboat.

A few manatees are attracted to anchored boats and may even chew

or play with anchor lines. Some manatees are attracted to

snorkelers and roll on their backs to be scratched. The majority

of manatees, however, ignore human attention or appear to avoid it

by moving into the manatee sanctuaries or swimming out into colder

portions of the bay (Patrick Hagan, pers. comm.).

The reactions of individual manatees, although easily seen,

are difficult to quantify. They suggest, however, that human

waterborne recreational activities may affect a large proportion

of manatees wintering in Kings Bay. A study to determine the

nature of this interaction was proposed by Packard (1983), by the

Florida Manatee Recovery Team (USFWS, 1989) and by Project Leader

Glenn Carowan of the Chassahowitzka National Wildlife Refuge

complex. To evaluate the impact of human activities on manatees

in Kings Bay, I investigated changes in manatee abundance and

distribution in response to different levels of human use.

The study had the following objectives:

1. To observe the manatees that use Kings Bay, Crystal

River, Florida throughout the winter and to plot

their relative use of southern end of Kings Bay

(South Bay) and its sanctuaries on days with

differing levels of human activity.

2. To determine the relationship among human waterborne

activities, temperature, and manatee use of Kings


3. To make management recommendations, if necessary,

to minimize any negative impacts of human

water-borne activities on the Crystal River manatees

while they are using this critical winter habitat.


Kings Bay and the city of Crystal River are located on

Florida's west coast in the Big Bend area, approximately 150 km

(90 miles) north of Tampa (Fig. 1). The bay is approximately 1

km (0.625 miles) wide and 2 km (1.25 miles) long. It contains

several large springs, most notably the cluster around King's

Spring south of Banana Island, and numerous smaller springs which

together form the headwaters of the Crystal River (Figs. 1 and 2).

The 11 km (6.6 mile) long river empties into the Gulf of Mexico.

The total output of the springs is affected by tides and

rainfall. The average output from 1964-1975 was estimated to be

25.9 cubic m or 2.25 million kl (600 million gal.) of water per

day (Hartman, 1974). Because the springs are fed by the Floridan

Aquifer, the water issuing from the springs remain a constant

23.7'C (74.7'F).

Most of Kings Bay is between 1 and 3 m (3 to 9 ft) deep with

the exception of some of the larger springs, which are 10 m (30

ft) or more in depth. A study presently underway by the Southwest

Florida Water Management District (SWFWMD) should reveal the

effects of tidal influences on the bay's salinity. Tides also can

cause up to 2 m (6 ft) of variation in depth (Hartman, 1974) but

the typical daily variation is about 1 m (3 ft) (Jim Reid, pers.

comm.). Strong winds seem to accentuate or counteract tidal

influences and hurricanes can greatly increase the tidal effect and

may drastically increase salinity (Rosenau et al, 1977).


The South Bay, defined as the area of approximately 120

hectares (300 acres) south of Banana Island and Warden Key,

contains King's Spring (also called the Main Spring) and

neighboring springs. These springs are considered to be

responsible for the largest outflow of warm water in the bay.

King's Spring itself is around 22 m (75 ft) across, with a 9 m (30

ft) deep hole. Two entrances at the bottom lead to a 15 m (50 ft)

wide cave that is 18 m (60 ft) deep. The flow of water from this

spring is light. Stronger flows issue from both Grand Canyon

Spring, a 10 m (35 ft) long crack adjacent to King's Spring and

Mullet's Gullet, a series of small springs 30 m (100 ft) east of

King's Spring (DeLoach, 1986). Banana Island and Warden Key may

help protect the South Bay from wind and tide driven currents that

would mix with and cool the warm water.

The study area consisted of a portion of Kings Bay south from

the middle of Buzzard Island including the canal system fed by

Magnolia Spring (Figs. 1 and 2). The area covered by the aerial

surveys was about 2.4 km (1.5 mi) by about 3.2 km (2 mi) and

contained about 405 ha (1013 acres) of water. The area contained

all three manatee sanctuaries, the two largest springs (Magnolia

Spring and the King's Spring cluster) and the South Bay area

described above (Fig. 2).

The principal downtown area of Crystal River is on the

northern and eastern shores of Kings Bay and the area around the

bay is developing rapidly. Much of the bay is surrounded by

subdivisions and most of the shoreline has seawalls. Dredge and

fill operations have modified the eastern and southern shore of

the bay. However, the freshwater marsh on the western shore

remains virtually undeveloped.

Many of the houses in the subdivisions have boat docks and

residents are requesting additional dock and building permits on

the bay and the river. Both Sunset Shores and Magnolia Springs

manatee sanctuaries have docks within their boundaries and

additional dock-building could occur if permits were obtained.

Local residents and guests are allowed direct boating access to

and from their docks.

The number of boats using Kings Bay is increasing. During

the winter months, the number of boats clustered around the South

Bay's main spring and the adjacent two manatee sanctuaries has

increased. Packard (1983) reported as many as 33. Public use

reports from the Crystal River National Wildlife Refuge for the

last few years indicate that the presence of 50 or more boats in

this area is no longer uncommon.

Kings Bay is an increasingly popular year-round SCUBA diving

resort. Dive instructors from both in- and out-of-state often

bring classes to Crystal River for open-water diving certifications

and, in winter, for manatee encounters. Large numbers of people

also come independently for diving, fishing, snorkeling and

recreational boating opportunities. The tourists using Kings Bay

produce significant revenue for the city, particularly for the

local dive shops, marinas, restaurants and motels which cater to

waterborne recreational activities. As public use has increased,


so have revenues. For five dive shops and three motels closely

associated with Kings Bay, total sales more than doubled between

1980 and 1986 (Milon, in prep.). The first quarter of the year

(January-March) is the period when most dive shop operators feel

the presence of manatees most influences their business. In each

of the six years above, sales during the manatee season accounted

for between 28 and 53% of the sales for the entire year (Milon, in


As the number of residents and tourists increase so does the

public pressure to control aquatic weeds, such as Hvdrilla and the

algae Lvnabva, which limit the use of the county's waterways. As

a result, Citrus County has the third largest public aquatic weed

control program in Florida (Center for Aquatic Plant Research,


Since the 1960's manatees have been known to use Kings Bay as

a winter thermal refuge (Hartman, 1974) and the maximum number of

animals aggregating in the bay has been steadily increasing.

Hartman (1974) reported 63 animals present in the area during the

winter of 1967-68 whereas the Crystal River National Wildlife

Refuge reported 162 in Kings Bay alone in December 1987. At this

time, the largest manatee aggregations known to occur in a natural

warm-water refuge are found in Kings Bay (Kochman, et al., 1985).

The Crystal River National Wildlife Refuge (part of the

Chassahowitzka NWR complex, administered by the U. S. Fish and

Wildlife Service) was created in 1983 specifically to protect the

manatee in the midst of these potential impacts. However, the


43-acre Refuge consists only of nine undeveloped islands, the

submerged lands associated with them (including the largest spring,

referred to as King's Spring) and a few scattered lots (mostly

undeveloped) on the mainland. The greater part of the Kings Bay

shoreline is privately owned. With the exception of a small area

owned by the federal government, the water bottom and the water

column belong to the State of Florida. The Refuge has no direct

control over developments that occur anywhere other than on Refuge


However, as an endangered species, the manatee falls under

the protection of the Endangered Species Act of 1973 which makes

the "taking" of an animal unlawful. One category of "taking" is

"harassment". Harassment is defined in the Act (50 CFR 17.3(c))

as "an intentional or negligent act or omission which creates the

likelihood of injury to wildlife by annoying it to such an extent

as to significantly disrupt normal behavioral patterns which

include, but are not limited to, feeding or sheltering." Refuge

Law Enforcement authority gives the officers of the Crystal River

NWR the authority to enforce any regulations concerning harassment

of the manatee whether they are technically on Refuge property or

not. The Refuge is empowered to:

1) Enforce state and federal laws related to the Endangered

Species Act and the Florida Manatee Sanctuary Act. These

include harassment violations, speed zone regulations and

sanctuary violations. (The Refuge cannot enforce county


or local laws, although an effort to change this is being


2) Monitor the Big Bend manatee population, in cooperation

with the USFWS Sirenia Project, National Ecology Research

Center, Gainesville, FL.

3) Monitor positive and negative effects on manatees,

including impacts on vegetation, water quality, and human

recreational activities.

4) Provide interpretive education opportunities to the


5) Serve in an advisory capacity by providing information

and recommendations for the protection of the manatee to

the FWS Enhancement Office in Jacksonville which in turn

provides biological opinions to the Corps of Engineers

as well as leadership for other manatee recovery


6) Implement emergency measures, such as extending the dates

that idle speed zones or manatee sanctuaries are in

effect in response to weather conditions and

corresponding changes in manatee use patterns.

If the existing level of human recreational activity in Kings

Bay constitutes harassment of the manatee population, the

Endangered Species Act requires the U. S. Fish and Wildlife Service

to take steps to correct the situation.


To determine the number and distribution of manatees and boats

on days of differing levels of human use, simultaneous ground and

aerial surveys were conducted on two mornings each week from

January through March 1988 and November 1988 through March 1989.

Beginning at first light, or as soon afterward as possible, five

20-30 minute surveys were flown in fixed loops over the study area

at one hour intervals. Based on Packard's (1985) recommendations,

aerial surveys were flown in a Cessna 172 airplane at an altitude

of 150-225 m (500-750 ft) and an air speed of 128 km/hr (80 mph).

On two occasions a Cessna 172 was unavailable and a Cessna 152 was

used. Altitude and air speed remained the same. Unexpectedly, the

FAA canceled the project's waiver to fly below 300 m (1000 ft)

because of complaints by nearby residents. Therefore, surveys

after December 24, 1988 were flown at 1000 ft. Crystal River

Refuge Biologist Larry Hartis, who has flown the surveys for the

Refuge for the past four years, believes the 300 m (1,000 ft)

altitude did not reduce the accuracy of his counts. On six days the

Refuge surveys coincided with those of this study. The counts were

within 5% of each other on these dates.

During aerial surveys, one observer counted manatees while

the other counted boats. Three individuals alternated as manatee

observers over the course of this study and a total of eight others

counted boats. Manatees and boats were plotted on separate grid

maps by the observers. Manatees were categorized as being adults

(large) or calves (small and associated closely with an adult).


Boats were divided into 'three size categories: Small: canoes,

kayaks, rubber boats boats capable of carrying about 3 people;

Medium: jon boats boats less than 20 feet long, capable of

carrying between 4 and 8 people; and Large: barges or other boats

over 20 feet long capable of carrying 8 or more people.

Individuals counting manatees were trained by an experienced

observer and had at least four supervised flights before collecting

data. Individuals counting boats were briefed as to size

categories prior to their first flight.

Simultaneously, ground observers were stationed at three

points in Kings Bay. Two boat stations, each consisting of a 3 m

(10 ft) wooden ladder tied to the deck of a boat, were anchored in

the two channels used by manatees to enter and leave the South Bay.

One channel is located west of Banana Island and the other west of

Warden Key (Fig. 2). A third station was located midway across the

bridge over the canal leading to Magnolia Springs manatee

sanctuary. Observers were able to count the number of people in

boats and to see or ask what activities they were planning to

engage in.

Beginning at dawn and continuing through the fifth aerial

survey each study day, observers at the three stations continuously

recorded the following information: 1) time of each observation,

2) air and surface water temperatures at approximately half-hour

intervals, 3) direction of travel of each passing boat, 4) the

boat's size category, and 5) the number of people involved and the


activity they were planning to engage in (such as snorkeling,

diving, observing or fishing).

Surveys were conducted on two days each week. Because the

purpose of the study is to compare manatee movement patterns on

days of differing levels of human use, Wednesdays and Saturdays

were sampled. Wednesday were chosen because they usually

experienced lower public use levels and because, separated from

the weekend by two days, any residual effects of the heavier public

use on weekends would be lessened. By scheduling surveys for

Wednesday, it also was possible to reschedule on the following day

in the event undesirable weather conditions prevented the Wednesday

flights. Thursday were also lower public use days.

Saturday were chosen because they were characterized by

higher levels of public use activities. In case of undesirable

weather the surveys could be rescheduled for the next day, Sunday,

also a higher public use day.

Two days each week were sampled when possible. Due to rain

or fog not all study days were successfully completed. Successful

days were those defined as containing 4 or 5 aerial surveys.

Combining the two seasons there were a total of 29 successful

survey days out of a possible 50 (58%). The second (complete)

season accounted for 22 of the successful days out of a possible

36 (61%). There were a total of 139 separate survey flights.

The first year's field season began in January 1988 and ran

through mid-March 1988. This was considered a period of pilot

study, as it did not cover the entire season and was used to refine


survey techniques. However, some of the data collected were used

in this report. The second field season began in November 1988 and

ran through mid-March 1989. These are the months when the water

temperature in the Gulf is lower and manatees typically aggregate

in Kings Bay (Kochman et at., 1985).

Logistic regression (McCullagh and Nelder, 1985) was used to

examine manatee distribution in the South Bay and the South Bay

sanctuaries in relation to selected environmental factors,

including air temperature, water temperature and number of boats.

The probability of manatee occurrence in the South Bay and

sanctuaries was modelled as a linear function of the environmental

variables, allowing the important factors to be identified and

resulting in the derivation of descriptive models. Logistic

regressions were fitted using the GLIM software package (Numerical

Algorithms Group, 1986). In logistic regression, the

logit-transformed probability, 1() is modelled as a linear

function of the explanatory variables, such that

i(A) = -B + &,Aj + &Xp, where

1() =In I
1 i-)

Predicted probabilities, g, can be back-transformed from logit

scale as A =
1 +

To verify the required assumption that observations made on

different flights were independent, variance components were

estimated in a mixed model to test the effects of season,


week-within-season, and day-within-week-season on the

arcsin-transformed proportion of manatees in the South Bay and the

sanctuaries. Each model also contained the same fixed-effect

covariates as in the logistic regressions. Variance components

were based on modified maximum likelihood estimates from the SAS

MIXMOD procedure (Giesbrecht, 1984) and were divided by their

standard errors to yield t-statistics for significance tests.


Test for independence among flights

Based on the variance component analysis, the proportion of

manatees in the South Bay occurring in the sanctuaries appeared to

be independent among flights. None of the variance components was

significant (Table 1). Similar results were obtained for the

proportion of study-area manatees in the South Bay, with the

possible exception that variation among days within week-season was

larger than expected (t = 2.12; P < 0.05).

Air and water temperature effects

Mean air and water temperatures were defined as the average

of the temperatures measured at the two South Bay stations,

averaged for each flight-hour. The temperatures taken at the

Magnolia Springs station were not used in the analysis because they

are unlikely to directly affect the manatees' use of the south bay

and the south bay sanctuaries. Mean air and water temperatures

were highly correlated ( < 0.001) (Fig. 3).

Manatee use of the South Bay

The probability of study area manatees occurring in the South

Bay was primarily affected by an inverse relationship with water

temperature (E < 0.05), and was secondarily influenced by air

temperature (E <0.01) as indicated by logistic regression (Table

2, Figs. 4 and 5). Neither the total number of boats in the study

area, nor the number of boats in the South Bay were an important

correlate of manatee occurrence in the South Bay when added to the

model (Q > 0.25) (Figs. 6 and 7).

Water temperature seems to be more important than air

temperature in determining manatee behavior (Irvine, 1983).

Hartman (1974) found a correlation between the drop in the water

temperature of the Gulf of Mexico each autumn and the increase in

the number of manatees in Kings Bay. He also found that a drop in

air temperature to 59*F (15'C) or lower stimulated manatees to

aggregate near the springs, perhaps in anticipation of lower water

temperatures to follow. This study showed that the number of

manatees using Kings Bay and the South Bay springs increased as

water temperatures in the bay fell. Between November and March,

as long-as the water temperatures in the Gulf and the bay remained

cool, regardless of air temperature, some manatees usually could

be found near the springs, particularly in the cooler early morning



Water temperatures equal to or below 68*F (20'C) increase

energetic demands on manatees, suggesting that 68*F is the minimum

water temperature suitable for long-term use by manatees (Irvine,

1983). "Mean water temperatures averaging equal to or below 68F

occurred on three survey days during the first season and two days

during the second, in February of both years (Fig 8). On two of

those days, average temperatures determined during all five morning

hours were below the critical temperature. On two other days, two

of five survey hours averaged below 68"F, with temperatures during

the remaining hours averaging just over 68'F. The remaining day

showed mean temperatures below 68'F only during the first hour.

Average water temperatures at the stations tended to increase over

the morning hours (Fig. 9) although on very cold days there was

little or no change.

Manatee use of South Bay sanctuaries

The probability of the South Bay manatees using the

sanctuaries showed a highly significant positive relationship with

the number of boats in the South Bay (P < 0.001), in addition to

an inverse correlation with water temperature (E < 0.001) (Table

3, Fig. 10). The addition of an air temperature variable did not

significantly improve the fit of this model (P > 0.17). The E

values for the South Bay and sanctuary models were 0.3665 and

0.3565, respectively.

It is important to keep in mind that the model explains only

about 36% of the variability in the relationship among water


temperature, number of boats and manatee use of sanctuaries.

Additional non-random factors may also influence the relationship

among these variables. Discovery of these factors may well result

in development of a better predictive model. In the meantime,

predictions from this model should be interpreted cautiously.

Examples of factors that were not taken into account in this model

because data could only be estimated were the number of people per

boat, the number of snorkelers and divers among them and the

intrusiveness of the swimmers. The number of boats is a fairly

crude way of estimating human impact on manatees. Any management

based on limiting the number of boats in an area should take into

account that the number of people per boat varies with the size of

the boats, days of the week, and their type of activity varies as


Of the 134 surveys, 35 were conducted when 25 or more boats

were present. In 22 of those 35 surveys (63%), more than 50% of

the manatees in the South Bay were in the sanctuaries, representing

14.5% of the study area. Of the 99 surveys during which fewer than

25 boats were present, only 35 of the 99 surveys (35%) showed more

than 50% of the manatees in the sanctuaries. With only two

exceptions, whenever the number of boats exceeded 35, over 50% of

the manatees in the South Bay were in the sanctuaries.

Public Use Information

Observers at the ground stations collected public use

information on 1436 of the thousands of boats that used Kings Bay


during the 1988-89 winter. Because the boats using Magnolia

Springs probably do not have a direct affect on the manatees in the

South Bay, its data are displayed separately (Table 4.). There

were generally fewer people in each boat observed at the Magnolia

Springs station compared to the South Bay stations. A larger ratio

of residents to visitors probably accounts for the lower number of

people per boat at Magnolia Springs. A large boat at Magnolia

Springs is probably a privately-owned boat whereas in the South

Bay, it is likely to be a rented dive barge.

There was a difference in the pattern of public use on weekday

mornings versus weekend and holiday mornings. Overall, boats using

the South Bay averaged about one additional person per boat on

weekends and holidays compared to weekdays (Tables 5 & 6; Fig. 11).

The same pattern holds true for Magnolia Springs. Most of this

increase was due to an average of 2.05 more people per large boat

on the weekends, probably because there were more dive barges

present. The much higher average number of boats in the South Bay

on weekends and holidays was due to the increase in the number of

medium-sized boats, by far the largest category of boats. There

were 2.96 times as many medium-sized boats on weekends and

holidays, due to the high number of jon boats rented to divers and

snorkelers (Fig. 12). There were also 2.91 times as many large

boats present on weekends than on weekdays and 8.57 times as many

small boats present on weekends. Magnolia Springs showed a similar

pattern. On weekday and weekend days alike, roughly 65% of the

boats passing the observation stations were in the medium category,

a little over 25% were large, and less than 10% were small canoes

or rubber boats.

More boats and more people per boat resulted in a greater

estimated number of people using Kings Bay on weekends and holidays

than on weekdays (Fig. 13). On weekdays and weekends alike, around

half the people observed were in medium-sized boats and about half

were in large boats, with about 4% or fewer in the small boat

category. On any given weekend or holiday, there were likely to

be an average of over three times as many boats and over three

times as many people present in the study area as on a weekday.

The use category that shows the most dramatic contrast between

weekend and weekdays is diving (Table 7, Fig. 14). To estimate the

number of people actually engaging in each activity, we used the

maximum number of boats present in each category for each survey

day. Because there was some unmeasured turnover throughout the

morning, this still underestimates the total number of boats that

used the area, but less so than other parameters, such as the mean

number of boats per survey day. Combining the Magnolia Springs and

South Bay data from Table 7 and multiplying the overall percentage

of people engaged in each activity by the number of boats, there

were an estimated nearly 5 times as many divers in the study area

on weekends than on weekdays (Table 8). There were also over 4

times as many snorkelers.

These counts only covered the morning hours. Several years

of public use survey reports compiled by the staff of the

Chassahowitzka NWR complex show there is at least one complete

turnover of people each day. People seeking manatee encounters,

therefore, commonly rent boats for a half-day rather than a

full-day. An estimated number of people using the study area for

the entire day would therefore be two times the number shown.

Using this estimate approximately 32,480 people used the study area

between November 1, 1988 and March 12, 1989 (Table 9). This is an

underestimate of public use of the entire bay because the study

area includes only roughly 2/3 of Kings Bay and the maximum number

of boats present in any single survey is less than the total

present over the 5-hour study period.


The manatee's requirement for warm water sanctuaries is

critical during cold periods in the winter (Cahn, 1i40; Hartman,

1974; Shane, 1983). Although manatees are capable of fairly

extensive forays into 68'F (20'C) or cooler water, prolonged

exposure to cold water not only imposes increased energetic demands

on them but can cause their deaths (Irvine, 1983; O'Shea et al.

1985). The animals arriving in Kings Bay in response to falling

Gulf temperatures were therefore experiencing varying degrees of

physiological stress. Unlike other marine mammals, which eat high

energy and high protein diets of fish or other sea creatures and

have relatively high metabolic rates, manatees eat low energy and

low protein aquatic vegetation. Manatees feed for approximately

4 to 6 hours each day, probably depending on temperature, forage

quality and their nutritional needs (Etheridge et al., 1985;


Bengtson, 1983). Their metabolic rate is considered unusually low,

and they have high thermal conductance (Irvine, 1983). Factors

which disrupt their normal routines, prevent them from feeding or

resting or cause them to move unnecessarily may add stress.

Manatees gathering near the warm spring heads may be under the most

stress and added stress over long periods, such as for an entire

winter, may affect their health and their ability to reproduce.

Activities that threaten a manatee's well-being are defined as

harassment under the Endangered Species Act.

Sanctuaries were implemented in Kings Bay beginning in 1980

to prevent such harassment. The Refuge enforces them during the

winter months when manatees use the area. Boats and people are

excluded from areas near the largest outflows so that manatees can

rest and socialize in relatively warm water without interference.

However, the number of animals using Kings Bay is steadily

increasing. During the 1977-78 winter a maximum count of 78

manatees was recorded in Kings Bay (Kochman et al., 1985). Four

years later that number had increased two-fold to 162 (December 10,

1987) (Crystal River NWR Annual Report 1987). This past winter the

maximum count was 246 (December 28, 1989) (Larry Hartis, pers.

comm.). The sanctuaries were not designed to accommodate this

large an increase in the manatee population.

This study has shown that manatees come to Kings Bay,

particularly the South Bay, in response to air and water

temperatures, regardless of the number of boats present. One of

the concerns that led to this study was the possibility that


manatees were being driven out of the South Bay by the weekend

crowds of people. This appears not to be the case. Manatees are

continuing to use the South Bay, but they are disproportionately

spending-time in the sanctuaries, regardless of weather conditions,

in direct relationship to the number of boats present. This

finding agrees with the findings of past research (Kochman, et al.,

1985). The two sanctuaries in the South Bay, while representing

only about 14.5% of the surface area, often contain over 50% of the

manatees. On days when fewer boats are present, a larger

proportion of the animals remain outside the sanctuaries feeding,

resting, interacting with other manatees or interacting with

people. In light of this information it is apparent that the

presence of increased numbers of boats in the South Bay

significantly alters the way manatees use this critical habitat by

disproportionately confining them to smaller areas. This situation

constitutes harassment as defined by the Endangered Species Act

because normal behavioral patterns have been significantly

disrupted. The following recommendations suggest placing

restrictions on human waterborne activities where they conflict

with the Endangered Species Act. Kings Bay is recognized as an

important recreational resource, to a great degree because of the

presence of manatees. The intent of these recommendations is the

protection of that resource for the benefit of residents, visitors

and business operators for years to come.


1. Limit the number of boats in the South Bay.

The predictions of the logistic regression model can be used

as guidelines for estimating the maximum number of boats to be

allowed in a designated area at certain specific water temperatures

(see Fig. 11). The Refuge could issue a limited number of permits

to boat rental companies and boat launching facilities based on

current water temperatures and estimates of upcoming weather

conditions. To accommodate more people, permits could be for a

limited period of time. Restrictions would not prevent residents

and businesses from passing through the South Bay but would be for

the purpose of reducing the intensity of human activity to a level

where its impact on the manatees is minimal, i.e. where they are

not disproportionately using the sanctuaries.

As mentioned earlier, any restriction on the number of boats

should take into account that the number of people per boat varies

with the size of the boats and with the days of the week. The

number of people and their behavior is likely to be an important


2. Schedule hours when the South Bay is closed to boats

Restricting the number of hours boaters and divers are allowed

access to manatees would solve several problems. Manatees would

be assured of having sufficient time to feed and rest in warm water

areas yet still be available to the visiting public for several


hours a day. Hours could be chosen that would be convenient for

visitors and profitable for local businesses. Scheduled open hours

could be consistent, which would allow visitors, businesses and law

enforcement personnel to plan their activities. Alternatively,

hours could be flexible and based on water temperatures. In cold

weather, closing a portion of the South Bay during night and early

morning hours when water temperatures are lowest is recommended.

Closure of King's Spring, adjacent to the Banana Island sanctuary,

is controversial because it is a popular dive spot and affords

excellent manatee viewing, especially in the early morning hours

when the animals are resting, before they are disturbed. Although

King's Spring is not in itself the source of the greatest flow, the

shallower areas surrounding it, particularly on the northeast side,

are a favorite resting spot for large numbers of manatees (often

30 or more) on cool nights. Reduced early morning disturbance

should be a priority, because temperatures are cooler, and manatees

are more likely to require thermal refuge. King's Spring and the

adjacent area should be protected during early morning hours,

particularly when water temperatures are low.

3. Create new sanctuaries

Increasing the area of the sanctuary system would provide

space for the increasing number of manatees appearing in Kings Bay

each' winter. Adding additional sanctuary areas would provide

protected foraging areas as well. Manatees that disperse daily

to feed throughout Kings Bay may be moved several times in the


Course of a day as they are discovered by boaters and divers. In

cold weather the time spent in unnecessary travel between foraging

sites could either reduce their total feeding time or force

manatees to feed at night when temperatures are significantly

colder. On very cold days, manatees do not disperse to feed but

remain near the springs for warmth, feeding only in the immediate

area. At times of high public use, a large proportion of them

further restrict themselves to the sanctuaries. The winter of

1988-89 was a very mild winter and aquatic plants were still

present in the sanctuaries in March. During the preceding winter,

however, the eastern end of the South Bay (including the two

sanctuaries) was virtually devoid of vegetation by the end of

January (Patrick Hagan, pers. comm). This appears to be true of

the 1989-90 season as well. Because Florida often has one or two

severe cold periods in late spring, the opportunity exists for

manatees to deplete the food supplies in the sanctuaries in

response to human pressure and then be forced to go without food

should a late cold front confine them to the area. The risk to the

manatees would be further increased if the cold front coincided

with several high-use days (such as Spring Break periods when

schools and colleges have vacations), when a disproportionate

number of manatees use the sanctuaries. Creating foraging

sanctuaries near, if not in, warm water areas could protect

sanctuaries' resources from overexploitation in response to human

pressure. Recommended locations for additional sanctuaries are

shown in Fig. 16. These areas have been identified as manatees'


preferred foraging areas by Refuge and Sirenia Project surveys and

by Kochman (1983).

Reducing the foraging pressure in the South Bay also would

mean sufficient food would still be present in the event of a

hurricane or severe tropical storm. In 1985, hurricane Elena

forced a salt water wedge into Kings Bay, raising the salinity and

killing a large proportion of the Hydrilla, the principle food for

manatees in Kings Bay. This reduction occurred in August at the

end of the growing season and just before the beginning of manatee

migration into the area. Refuge vegetation sampling data showed

that it took two years for it to return to its former abundance

(USFWS, 1987). Hydrilla is an introduced aquatic plant, widely

disliked by boaters for its rapid growth and propeller-entangling

qualities. Despite aquatic weed control by chemical and mechanical

means, it has supplanted many of the native, somewhat salt-tolerant

species and now comprises 80% of the aquatic vegetation in Kings

Bay (Haller and Shireman, 1982; Kochman, et al., 1985). Although

under normal circumstances Hydrilla provides an abundance of food

for the winter population of manatees, it can be quickly devastated

by water of higher salinity. It is possible that without Hvdrilla

the amount of remaining vegetation in Kings Bay would not be

sufficient to feed the growing number of manatees that now use the

area. After the storm damage in 1985, there was concern that

sufficient food would not be available for the manatees for the

rest of that winter and contingency plans were made to establish

additional emergency sanctuaries. Because the South Bay is the


area least likely to be affected by storm-driven salt water

intrusion, care should be taken to prevent premature overgrazing

of the area.

4. Expand the area of existing sanctuaries

Because manatees choose to use the South Bay at high densities

regardless of the number of boats, more of the area should be

included in sanctuaries. The present sanctuaries could be enlarged

without unduly impacting human activities.

Outside the manatee sanctuaries in the South Bay, a boat-free

buffer zone could be established where snorkelers, divers and

manatees could interact. The situation at present allows

motorboats, snorkelers and divers to mix in the same area.

Although to my knowledge only manatees, not people, have been

struck by boats, the possibility of human injury exists. A buffer

zone would provide a measure of human safety that is presently

missing. A well-marked channel between the protected areas, marked

by buoys to be used for tying boats, could reduce the hazards of

carelessly dropped anchors and reduce the number of drifting boats.

Canoes, kayaks and other paddle driven craft could be allowed in

the buffer zone, at the discretion of the Refuge. Any future need

to restrict the number of boats in the eastern half of the South

Bay could grow naturally out of such a plan by limiting the number

of "parking places" and disallowing anchoring all together. Human

activities not centered around the manatees should be encouraged

to use the channel east of Banana Island when possible. A


sufficient channel through the South Bay would be maintained for

the homeowners and businesses on the southern and eastern shores

whose craft are too large for that channel.

In a recent survey of 300 visitors to Kings Bay, expanding

manatee sanctuaries was the most preferred method of preventing

manatee harassment (Buckingham, 1989).

5. Additional Recommendations

a) Evaluate the effects of divers and snorkelers to more

closely determine human impacts.

My observations and those of others reveal a wide variation

in responses of people to manatees and of manatees to people.

According to Crystal River NWR Project Leader Pat Hagan, boaters

who arrive in small numbers, quietly paddle in and snorkel quietly

floating on the surface often attract the attention of curious

manatees which respond by approaching. Those people arriving in

large crowds with noisy outboard motors, wheezing SCUBA regulators

and a tendency to crowd or chase the animals often find the objects

of their attention heading for the sanctuaries and remaining just

out of reach. Illegal actions, such as grabbing, riding, and

separating a mother and calf also occur with regularity despite

lists of prohibited activities available to visitors in the form

of leaflets, information from local dive shops and general coverage

by the media. In the recent survey of visitors to Kings Bay, over

37% reported having seen incidents of harassment (Buckingham,

1989). The actions of the boat occupants may account for much of


the variation remaining in our model. Further study is needed to

narrow down these variables to a measurable component which can

then be added to the model. These studies will require

observations of manatee behavior in the absence of these activities

for comparison. Closing the bay to all boating activity for a few

select days would be the best way to accomplish this.

b) Night diving in King's Spring should be restricted. I

have observed on several occasions manatees retreating from divers

with lights. If dive-lights bother a large proportion of manatees,

use of those lights should be limited. In cool weather, air

temperatures at night can drop considerably and manatees are more

likely to require thermal refuge. Therefore, night-diving in

Kihg's Spring, if it is allowed at all, should occur only when the

air and water temperatures have been warm for several days, at the

discretion of the Refuge. Possibly a stationary light could be

placed in the spring on a few warm winter nights to see if manatees

avoid it. A non-moving light may be less frightening to the

manatees and may even attract them once they become accustomed to


c) Federal, state and local agencies need to work together

to provide additional law enforcement in Kings Bay. Signs

indicating speed zones should be consistent and clear, personnel

schedules should be coordinated so that maximum coverage is

achieved, and an effort should be made to educate members of the

judiciary so that violators are prosecuted to the full extent of

the law. Respondents to the public use survey in 1989 strongly


favored an increase in the number of law enforcement officers in

the area (Buckingham, 1989) and many felt that fines accrued from

manatee harassment violations should be used for funding additional

manatee protection.

d) The idle speed zone currently in place in the eastern

end of Kings Bay in the winter should be extended to include a

greater proportion of the bay. On many days, especially in warm

weather, snorkelers and divers are widely dispersed throughout the

bay, sometimes separated from their boats and dive flags, and

usually swimming just below the surface among any number of

motorboats. Much of Kings Bay is currently a "slow speed" area

but the recent survey of visitors to Kings.Bay revealed that many

of them did not know what "slow" and "idle" speeds meant

(Buckingham, 1989). Half of the visitors overestimated the speed

they were allowed to go in the idle speed areas. Since many people

are new to the area, are renting boats they are unfamiliar with and

are ignorant of the speed laws, the situation should be considered

unsafe for both people and manatees. The recommendation to expand

the idle speed zone to prevent manatee harassment was one of the

three most popular choices by visitors.


This study shows that manatees using the southern part of

Kings Bay as a winter thermal refuge respond to increasing numbers

of boats by moving into the boat-free sanctuaries. This response

results in much higher than normal densities, particularly at times

of thermal stress. Manatees require room to rest, socialize, and

eat, and a limited amount of food exists in the sanctuaries; thus,

a case can be made for limiting boating activity in the South Bay,

expanding the existing sanctuary system or both. These

recommendations also make sense in light of the steadily increasing

number of manatees aggregating in Kings Bay each winter. The

present conflicts can be expected to increase if no action is


The Refuge has a number of alternatives for decreasing

conflict that can be implemented singly or in various combinations.

It can 1) control the number of boats present at any given time,

2) schedule the time periods when boats are allowed to share the

area with manatees, 3) enlarge existing sanctuaries and 4) create

additional sanctuaries. Research on the effects of diving and

snorkeling will lead to refinement of protection strategies.

Increased law enforcement presence and an expanded idle speed zone

would protect not only manatees but the public as well.


This report was reviewed by Lynn Lefebvre, Tom O'Shea, Wiley

Kitchens, Patrick Hagan and Joe Schaefer. Many thanks to the staff

of the Chassahowitzka NWR, especially Patrick Hagan and Larry

Hartis, for their tireless support of this project. I appreciate

Lynn Lefebvre, Sirenia Project, USFWS, for her consistent high

standards and sense of purpose and Howard Kochman, USFWS Sirenia

Project and Steve Linda, IFAS Statistics, for their statistical

expertise. Jim Reid and Tom O'Shea of the Sirenia Project

recommended future sanctuary locations. This project was funded

by the U. S. Fish and Wildl. Serv., Research Work Order No. 52 with

the Fla. Coop. Fish and Wildl. Res. Unit. Wiley Kitchens of the

Coop Unit and former Project Leader of Chassahowitzka NWR Glenn

Carowan were responsible for this project's concept, funding and

administrative support.

I wish to thank Robert Sheffield of Gator Aire, Gainesville

who skillfully piloted the aerial surveys. In Crystal River, I

greatly appreciated the hospitality and help we received from

Crystal Aero Group and Port Paradise Dive Shop.

Lastly, this study relied heavily on the dedication of Vincent

Condon, Bill Vordstadt and Marjorie Lamphear who flew the aerial

surveys and the 40 other volunteers who assisted in collecting

data. I am very grateful for their help.


Center for Aquatic Plant Research. 1987. Citrus County Aquatic
Plant Management. IFAS. University of Florida,
Gainesville,FL. 15 pp.

Bengtson, J. L. 1983. Estimating food consumption of free-ranging
manatees in Florida. J. Wildl. Manage. 47(4):1186-1192.

Brownell, R. L. 1980. West Indian Manatee Recovery Plan, USFWS.

Brownell, R.L., K. Ralls, and R. R. Reeves, eds. 1981. The West
Indian Manatee in Florida. pp. 3-26, in Proceedings of a
workshop held in Orlando, Florida, March 27-29 1978. Florida
Dept. of Natural Resources, Tallahassee, FL, 157 pp.

Buckingham, C. A. 1989. Crystal River National Wildlife Refuge
Public Use Survey Report. Technical Report No. 37.
Fla.Co-op. Fish and Wildl. Res. Unit. Univ. of Fla.,
Gainesville, FL. 102 pp.

Cahn, A. H. 1940. Manatees and the Florida freeze. J. Mamm.

DeLoach, N. 1986. Diving Guide to Underwater Florida. Ocean
Realm. New World Publications, Inc., Jacksonville, FL. 264

Endangered Species Act. 1973. 16 USC 1531-1543; 87 STAT. 884.

Etheridge, K., G. B. Rathbun, J. A. Powell, and H. I. Kochman.
1985. Consumption of aquatic plants by the West Indian
manatee. J. Aquat. Plant Manage. 23:21-25.

Giesbrecht, F. 1984. MIXMOD, a SAS procedure for analyzing mixed
models, North Carolina State University Mimeograph Series No.

Haller, W. T. and J. V. Shireman. 1982. Vegetative and herbicide
monitoring study in Kings Bay, Crystal River, Florida.
Project Report, U. S. Army Corps of Engineers Contract No.
DACW17-80-C-0062, Jacksonville, Florida.

Hartman, D. S. 1974. Distribution, status and conservation of
the manatee in the United States. Natl. Tech. Inf. Ser.,
Publ. No. PB81-140725. 246 pp.

-----. 1979. Ecology and behavior of the manatee (Trichechus
manatus) in Florida. Am. Soc. Mamm. Special Publ. No. 5. 153

Irvine, A. B. 1983. Manatee metabolism and its influence on
distribution in Florida. Biol. Conserv. 25:315-334.

Kochman, H. I., G. B. Rathbun, and J. A. Powell. 1983. Use of
Kings Bay, Crystal River, Florida, by the West Indian manatee
(Trichechus manatus). Pp. 69-124 in Packard, J. M. (ed.).
Proposed Research/Management Plan for Crystal River Manatees.
Vol. III. Compendium. Technical Report No. 7. Fla. Coop.
Fish an Wildl. Res. Unit. Univ. of Fla., Gainesville, FL.
346 pp.

Kochman, H. I., G. B. Rathbun and J. A. Powell. 1985. Temporal
and spatial distribution of manatees in Kings Bay, Crystal
River, Florida. J. Wildl. Manage. 49(4):921-924.

Lefebvre, L. W., T. J. O'Shea, G. B. Rathbun, and R. C. Best.
1989. Distribution, status, and biogeography of the West
Indian Manatee. pp. 567-610 in Woods, C. A. (ed.)
Biogeography of the West Indies: Past, Present, and Future.
Sandhill Crane Press, Inc. Gainesville, FL. 878 pp.

McCullage, P. and Nelder, J. A. 1985. Generalized Linear Models.
Chapman and Hall, Cambridge.

Milon, W. In prep. Economic activity associated with recreational
diving in Kings Bay, Crystal River, Florida.

Numerical Algorithms Group. 1986. The GLIM system, Release 3.77,
Generalized Linear Interactive Modeling, Oxford: Numerical
Algorithms Group.

O'Shea, T. J., C. A. Beck, R. K. Bonde, H. I. and D. K. Odell.
1985. An analysis of manatee mortality patterns in Florida,
1976-81. J. Wildl. Manage. 49:1-11.

O'Shea, T. J., J. F. Moore, and H. I. Kochman. 1984. Contaminant
concentrations in manatees in Florida. J. Wildl. Manage.

Packard, J. M. 1983. Proposed Research/Management Plan for
Crystal River Manatees. Volume I. Summary. Technical Report
No. 7. Fla. Coop. Fish and Wildl. Res. Unit. Univ. of Fla.,
Gainesville, FL 31 pp.

Packard, J. M. 1985. Development of manatee aerial survey
techniques. Manatee Pop. Res. Rep. No. 7. Tech. Rep. No.8-7.
Fla. Coop. Fish and Wildl. Res. Unit, Univ. Fla., Gainesville,
Fl. 68 pp.

Packard, J. M., Rathbun, G. B. and D. P. Domning. 1984. Sea cows
and manatees. pp 292-295 in D. Macdonald (ed.) The
Encyclopedia of Mammals, On File Publ., N. Y. 944 pp.


Rosenau, J. C., G. L. Falukner, C. W. Hendry, Jr., and R. W.Hull.
1977. Springs of Florida. Fla. Dept. Nat. Res., Bulletin No.
31, Tallahassee, FL. 461 pp.

SAS Institute, Inc. 1985. SAS/STAT Guide for Personal Computers.
Version 6. Cary, NC. 378 pp.

Shane, S. H. 1983. Abundance, distribution and movements of
manatees (Trichechus manatus) in Brevard County, Florida.
Bull. Amr. Sci. 33:1-9.

USFWS. 1987. Crystal River NWR Annual Narrative Report, 31 pp.
in Chassahowitzka National Wildlife Refuge Annual Report.

USFWS. 1989. Florida Manatee (Trichechus manatus latirostris)
Recovery Plan. Prepared by the Florida Manatee Recovery Team
for the U. S. Fish and Wildlife Service, Atlanta, Ga. 98 pp.

Table 1. Variance component t statistics from mixed model analysis.

I statistic

Variance component Prop. in sanctuary Prop. in South Bay

Season 0 0
Week (Season) 1.6 0.82
Day (Week, Season) 0.1 2.12*

P 0.05

Table 2. Parameter estimates for a model of the probability (0) that
a manatee in the study area will be in the South Bay for flight i:

1(0),= L + B, (water temp) + &2 (air temp), where 1 = the
logit transformation and i = 1, ...,132.

Parameter Estimate s.e. t statistic

S14.46 3.998 3.617***
j, -0.1885 0.06285 2.999**
2 -0.01934 0.009453 2.046*

P 0.01
** P 0.05
*** 0.001

Table 3. Parameter estimates for a model of the probability (0) that
a manatee in the South Bay will be in a South Bay sanctuary for flight

i(0)i = & + (water temp) + & (number of boats in South
Bay), where 1 = the logit transformation and i = 1, ...,131.

Parameter Estimate s.e. t statistic

B0 15.09 3.271 4.613***
B, -0.226 0.047 -4.868***
B2 0.039 0.006 6.171***

** P 0.001

Table 4. Number of people per boat for three size classes of boat,
counted as they passes the two South Bay observation stations and the
Magnolia Springs station.

Boat Size Number of % of All Number of % of All People/
Category Boats Boats People People Boat

Small 94 6.5 197 3.4 2.10
Medium 744 51.8 2368 40.5 3.18
Large 307 21.4 2408 41.2 7.84
Total 1145 79.7 4973 85.1 4.34'

Small 24 1.7 43 0.7 1.79
Medium 195 13.6 533 9.1 2.73
Large 72 5.0 297 5.1 4.13
Total 291 20.3 873 14.9 3.00'

2 average, not total

Table 5. Total number of boats and people per boat counted as they
passed the observation stations on the nine weekdays surveyed. Average
number of people per boat was calculated by dividing the total number
of boats by the total number of people for each boat size category.

Boats People
Boat Size X of ALL % of ALL People/
Category Number Average/day Boats Number Average/day People Boat

Small 7 0.78 2.7 12 1.33 1.4 1.71
Medium 141 15.67 54.9 356 39.56 40.5 2.52
Large 59 6.56 22.9 365 40.56 41.5 6.19
Total 207 23.00 80.5 733 81.44 83.4 3.54

Small 3 0.33 1.2 7 0.78 0.8 2.33
Medium 33 3.67 12.8 85 9.44 9.7 2.58
Large 14 1.56 5.5 54 6.00 6.1 3.86
Total 50 5.56 19.5 146 16.22 16.6 2.92

average, not total

Table 6. Total number of boats and people per boat counted as they
passed the observation stations on the thirteen weekend days and
holidays surveyed. Average number of people per boat was calculated
by dividing the total number of boats by the total number of people for
each boat size category.

Boats People
Boat Size % of ALL % of ALL People/
Category Number Average/day Boats Number Average/day People Boat

Small 87 6.69 7.4 185 23.00 3.7 2.13
Medium 603 46.38 51.2 2012 154.77 40.5 3.34
Large 248 19.08 21.0 2043 157.15 41.1 8.24
Total 938 72.15 79.6 4240 326.15 85.4 4.50

Small 21 1.62 1.8 36 2.77 0.7 1.71
Medium 162 12.46 13.8 448 34.46 9.0 2.77
Large 57 4.38 4.8 243 18.62 4.9 4.26
Total 240 18.46 20.4 727 55.92 14.6 3.03

Average, not total

Table 7. Number and percentage of total people passing the observation
stations engaged in each activity.

Diving Snorketing Fishing Observing Total

# % # % # % # %

Weekdays 232 35.0 60 9.1 34 5.1 215 32.5 541
Weekends 2046 52.7 654 16.8 118 3.0 500 12.9 3318

Weekdays 47 7.1 37 5.6 21 3.2 16 2.4 121
Weekends 296 7.6 61 1.6 106 2.7 105 2.7 568

Weekdays 279 42.1 97 14.7 55 8.3 231 34.9 662
Weekends 2342 60.3 715 18.4 224 5.8 605 15.5 3886

Table 8. An estimate of the number of people in the study area engaging
in each activity on an average morning, weekday or weekend/holiday.
This was calculated by averaging the product of the maximum number of
boats in the study area in each size category during the aerial surveys
and the proportion of people engaged in each activity calculated from
data from the three observation stations.

Diving Snorket ing Fishing Observing Total

Weekday 55.52 19.38 10.95 46.03 131.88
Weekend 268.24 81.85 25.80 68.95 444.84

Table 9. Estimated level of public use for the entire study area for
November 1, 1988 through March 12, 1989 calculated by averaging the
product of the maximum number of boats from aerial surveys and the
average number of people per boat from the combined observation station
data. There were 84 weekdays and 48 weekend days and holidays during
this period.

Average of Maximun
Boat Counts

Average Number of Daily
People per boat Turnover

Estimated Number of
People per day





















in Season


S a small, ex. canoes, kayaks, rubber boats boats capable of carrying up to around 3 people;
M = medium-sized, ex. jon boats boats less than 20 feet long, capable of carrying between 4 and 8 people;
L = large, ex. barges and other boats over 20 feet long, capable of carrying 8 or more people.

Fig. 1. Map of Kings Bay, Crystal River, Florida.

* so So

* '0o0 O000 300C *0O0 1*tx

Fig. 2. Map of Study Area.


Buzzard Island

Fig. 3. Correlation between air and
water temperature.

Men Air Temperatur (F)

m i S .

75* ..0

I 6 I

*. *0


35.0 48.8 62 7 76.3 90.0

Mean Wateir Temperature ( F)

. 68.35

35.0 48.8 62.5 76.3 90.0

Mean Air Temperature (*F)

Fig. 5. Proportion of manatees in South
Bay compared to water temperature.

Proportion of Manartee

-.8 ; .* : .'; ; .

.4 ... ;

A *

n i i -- i i i -- ,- I -

6 66 87 68 69 70 71 72 73
Mean Water Temperature ( F)
Nor: oat effect not Inoluded (N 132)

Fig. 6. Prop. of manatees in South Bay
compared to total number of boats

Proportion of Total Manatees

0.8 ..

o.e ,. *



0 20 40 60 81
Total Number of Boats in Study Area
Temp. effects Mt Inoluded (a 132)

Fig. 7. Prop. of manatees in South Bay
compared to no. of boats in South Bay.

Proportion of Total Manatees

0.8 .

0A I
* *

0.4 -

it : .

0 10 20 30 40
Number of Boats in South Bay
Tetos. effects met lomudle (n 134)

74 75

s0 0o

Fig. 8. Minimum average water
temperatures for each survey day.
Time e*lapoI between Survey days varis.

1 2 3 4 5 1 2 S 4 6 7 8 10 1 121 151 17 20

Fig. 9. Average water temperatures
over morning hours.

Temperature ( F)



70. -

70.6 -


T9 -


7-8 am

8-9 am

9-10 am

10-11 am 11-12 am

Fig. 10. Proportion of South Bay manatees in South Bay sanctuaries
as a function of water temperature and boat count. A contour of
the fitted response surface generated by the equation:

Logit of probability of a 15.09 0.2264 x (water temperature)
manatee in the south bay 0.03924 x (number of boats
being in the sanctuary in south bay)

For a given water temperature on the Y-axis, choose the
proportion of manatees in sanctuaries that may indicate boat
avoidance by manatees (e.g. over 50%), follow a horizontal line
from the temperature to the selected proportion and follow a
perpendicular line down to find the maximum number of boats. For
example, the proportion of manatees in the south bay using the
sanctuaries would be expected to reach 50% at 68 degrees F when 8
boats were in the south bay.




o .5


'. .7

z 68.3

66.0 4

18.5 33.0 49.5 66.0

Number of Boats in south bay

Fig. 11. Number of people per boat
weekdays vs. weekends in study area
age Number of Peope per Boat

mall Medium Large Total

C] WeIday Em Weekend
(Inoleds all 3 eoervatln station.)

Fig. 12. Estimated number of boats in
study area. Weekdays vs. Weekend days
Maximum no. In each category ach day.



Small Medium Large Total

M Weekday ~ Weekend

(From aerial urvey data.)

Fig. 13. Average number of people/day
in each boat size category.

Medium Large

SlWeekday jf Weekend

Fig. 14. Est. no. of people engaged
in each activity Weekdays vs. Weekends

Welldays E Weekends
(Frm arial and round station data.)

Fig. 15. Manatee Sanctuaries Current and Recommended.


Current Sanctuary

Recommended Sanctuary.',

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