TECHNICAL REPORT NO. 39
AN EVALUATION OF MANATEE DISTRIBUTION PATTERNS
IN RESPONSE TO PUBLIC USE ACTIVITIES
IN KINGS BAY, CRYSTAL RIVER, FLORIDA
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
U. S. Department of the Interior
Fish and Wildlife Service
Cooperative Agreement No. 14-16-00091544
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
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
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.
MATERIALS AND METHODS
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
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
Predicted probabilities, g, can be back-transformed from logit
scale as A =
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.
RESULTS AND DISCUSSION
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
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.
CONCLUSIONS AND RECOMMENDATIONS
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
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
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.
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
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.
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*
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 0.05
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
SOUTH BAY STATIONS
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'
MAGNOLIA SPRINGS STATION
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.
Boat Size X of ALL % of ALL People/
Category Number Average/day Boats Number Average/day People Boat
SOUTH BAY STATIONS
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
MAGNOLIA SPRING STATION
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.
Boat Size % of ALL % of ALL People/
Category Number Average/day Boats Number Average/day People Boat
SOUTH BAY STATIONS
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
MAGNOLIA SPRINGS STATION
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
# % # % # % # %
SOUTH BAY STATIONS
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
MAGNOLIA SPRINGS STATION
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
ALL THREE STATIONS
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
Average of Maximun
Average Number of Daily
People per boat Turnover
Estimated Number of
People per day
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.
Fig. 3. Correlation between air and
Men Air Temperatur (F)
m i S .
I 6 I
35.0 48.8 62 7 76.3 90.0
Mean Wateir Temperature ( F)
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 ... ;
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
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
it : .
0 10 20 30 40
Number of Boats in South Bay
Tetos. effects met lomudle (n 134)
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)
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.
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.
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.