• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 Recommendations
 Introduction
 Methods
 Results
 Discussion
 Summary
 Acknowledgement
 Reference






Group Title: Manatee population research report no. 8.
Title: Manatee response to interrupted operation of the Ft. Myers plant
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Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00073823/00001
 Material Information
Title: Manatee response to interrupted operation of the Ft. Myers plant winter 1984-85
Series Title: Manatee population research
Physical Description: 20 p. : ill., map ; 28 cm.
Language: English
Creator: Packard, Jane M
U.S. Fish and Wildlife Service
Florida Cooperative Fish and Wildlife Research Unit
Publisher: Florida Cooperative Fish and Wildlife Research Unit, University of Florida
Place of Publication: Gainesville Fla
Publication Date: [1985]
 Subjects
Subject: West Indian manatee -- Florida -- Fort Myers Region   ( lcsh )
Manatees -- Florida -- Fort Myers Region   ( lcsh )
Power-plants -- Environmental aspects -- Florida -- Fort Myers Region   ( lcsh )
Genre: federal government publication   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 20.
Statement of Responsibility: Jane M. Packard ... et al.
General Note: "Final report, 1985."
General Note: "Florida Cooperative Fish and Wildlife Research Unit for U.S. Fish and Wildlife Service"--Cover.
General Note: "Cooperative agreement no. 14-16-0009-1544."
General Note: "Research work order no. 2."
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: UF00073823
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 - 001893035
oclc - 27870071
notis - AJW8290

Table of Contents
    Title Page
        Title page
    Table of Contents
        Table of contents
    Recommendations
        Page 1
    Introduction
        Page 2
        Page 3
    Methods
        Page 4
        Aerial surveys
            Page 4
        Radio telemetry
            Page 5
        Environmental parameters
            Page 5
        Analysis
            Page 5
    Results
        Page 6
        Overview
            Page 6
            Page 7
            Page 8
            Page 9
        Distribution within the study area
            Page 10
            Page 11
        Behavior relative to temperature
            Page 12
            Page 13
        Movements relative to feeding areas
            Page 14
            Page 15
        Mortality
            Page 16
    Discussion
        Page 16
        Page 17
    Summary
        Page 18
    Acknowledgement
        Page 19
    Reference
        Page 20
Full Text






MANATEE RESPONSE TO INTERRUPTED OPERATION OF


THE FORT MYERS POWER PLANT

WINTER 1984/85


FINAL REPORT

1985


Jane M. Packard1, Kipp Frohlich2,
John E. Reynolds, III and J. Ross Wilcox4


1 Department of Wildlife and Fisheries Sciences
Texas A&M University
College Station, Texas 77843-2258
2 U.S. Fish and Wildlife Service Sirenia Project
412 NE 16th Ave., Rm. 250
Gainesville, FL 32609

Present address:
Florida Department of Natural Resources
100 Eighth Ave. S.E.
St. Petsburg, FL 33701

3 Biology Department
Eckerd College
St. Petersburg, FL 33733

Florida Power and Light Company
P. 0. Box 14000
Juno Beach, FL 33408


Prepared for:

U.S. Fish and Wildlife Service
75 Spring St. S.E.
Atlanta, GA 30303

Cooperative Agreement No. 14-16-0009-1544
Research Work Order No. 2


Citation should read: Packard, J.M., R.K. Frohlich, J.E. Reynolds, III,
and J. R. Wilcox. 1985. Manatee response to interrupted operation of the
Fort Myers power plant, winter 1984/85. Manatee Population Research Report
No. 8. Technical Report No. 8-8. Florida Cooperative Fish and Wildlife
Research Unit. University of Florida, Gainesville, Florida 20 pp.










TABLE OF CONTENTS


RECOMMENDATIONS

INTRODUCTION

STUDY AREA

METHODS

Aerial Surveys
Radio Telemetry
Environmental Parameters
Analysis

RESULTS

Overview
Abundance
Distribution within the Study Area
Behavior Relative to Temperature
Movements Relative to Feeding Areas
Mortality


DISCUSSION

SUMMARY

ACKNOWLEDGMENTS

LITERATURE CITED


PAGE










RECOMMENDATIONS

1. Although manatees have become accustomed to using power plants as
warm-water refuges, the extent of their dependency on refuges is
unknown. When a power plant that attracts manatees is scheduled to
change its operation schedule during the winter, this provides an
opportunity to investigate the question of dependency. The state and
federal manatee coordinators should be notified prior to any scheduled
changes and during any unscheduled changes in operation of any heated
effluent that attracts manatees.

2. Arrangements should be made such that the temperature of thermal
effluents attracting manatees does not drop below 19C when alternative
sites with warmer water are not available to manatees in the area. On
the basis of the present study, manatees appear to detect small
increments of temperature (1-2C), most will move to the warmer areas,
and some return to areas where they have previously found warm water.
In Fort Myers, most manatees appeared not to abandon the general area
of the traditional warm-water refuge, hence they would have been
exposed to severe cold stress during the coldest part of the winter if
the heated effluent had not been restored.

3. Changes in the distribution and visibility of manatees during a winter
when power plant operation is interrupted could influence the
consistency of an index designed to detect trends in manatee
abundance. More effort should be given to detecting and correcting
such potential bias in indices. For example, the distribution and
visibility of radio-tagged manatees could be monitored as an index of
changes in bias across winters. The possible use of automatic data
recording devices to monitor time spent by manatees near the surface,
or more visible radio-tags should be considered given the apparent
difficulties in reliably detecting radios from the.air.










INTRODUCTION

The degree to which manatees (Trichechus manatus) are dependent on
artificial thermal refuges in Florida has not been determined, although
their attraction to warm-water sites has been well documented (Hartman
1979, Irvine 1983, Powell and Rathbun 1984). Artesian springs in Florida
provide water of constant temperature throughout the year, attracting
manatees when ambient water temperatures drop below 20-23C (Hartman 1979).
In contrast, the heated industrial effluents that attract manatees may be
interrupted for mechanical or economic reasons, potentially exposing the
animals to cold stress.

The tropical distribution and seasonal aggregations of West Indian
manatees at thermal refuges in temperate Florida appear related to the lack
of physiological adaptations to withstand prolonged cold temperatures
(Irvine 1983). During three severe winters (1977, 1981, 1982), high
mortality has occurred among Florida manatees, especially in the late
juvenile/subadult size class (O'Shea et al. 1985).

Physiological studies indicate that manatees in general have a limited
capacity for thermogenesis (Irvine 1983, Gallivan, Best and Kanwisher
1983), suggesting that behavioral means of thermoregulation are important.
Possible behavioral responses contributing to short-term thermoregulation
include thermogenesis due to muscular activity, thermal taxis (directional
movement along a thermal gradient) and energy intake by feeding. At an
intermediate stage of cold exposure behavioral responses may no longer
function to warm the animal particularly when fat reserves are depleted.
Under conditions of prolonged cold, the lack of energy intake or inhibited
digestion of ingested food is likely to result in a cachectic condition
leading to death (Irvine 1983, O'Shea et al. 1985).

Interrupted discharge of the thermal effluent at a power plant near
Fort Myers provided an opportunity to examine the behavioral responses of
manatees in relation to changes in water temperature during the winter of
1984-85. The purposes of the study were to determine if manatees showed
the following behavioral characteristics related to thermoregulation: (1)
movement to alternative refuges as would be indicated by a change in
abundance compared to the previous year, (2) response to thermal gradients
within the traditional region of aggregation, (3) reduced movement out of
the study area to feeding areas, or (4) endurance of exposure to unusual
thermal stress, possibly leading to mortality.


STUDY AREA

The Fort Myers power plant is situated between the Caloosahatchee and
Orange rivers in southwestern Florida (Figure 1). The Caloosahatchee River
is joined by a cross-Florida navigation canal to Lake Okeechobee and flows
into the Gulf of Mexico in an area characterized by islands and broad
shallow bays. The Orange River is a small tributary of the Caloosahatchee
River. Water used for cooling purposes at the power plant is taken from
the Caloosahatchee River and discharged into a canal that extends to the
Orange River. The thermal plume warms the discharge canal, the Orange
River downstream from the discharge canal, and the Caloosahatchee River at





















































Location of aerial survey strata within the study area. The
Fort Myers power plant (P) is in the center of the intensive
search (I) and unit-recount (U) survey routes. The eastern
bounds of the intensive search and unit-recount surveys are at
the Franklin locks and Alva bridge, respectively. The western
bounds of the same routes are at the 1-75 and Cape Coral bridges,
respectively. The extreme bounds of the extended area (E) survey
route are at Estero Bay, northern Pine Island Sound and the Alva
bridge.


Figure 1.










the mouth of the Orange River. Water levels and flow in this river system
are influenced by tides and by water control structures such as the
Franklin locks on the Caloosahatchee River. Aquatic plants eaten by
manatees are present in shallow portions of the rivers, estuary and bays.

The study area was divided into four strata for the purpose of
allocating effort during aerial surveys (Figure 1). The primary stratum
included the area influenced by the thermal discharge of the power plant.
Stratum II included areas with aquatic vegetation near the power plant and
Stratum III included all other areas within 20 km on the Caloosahatchee
River and within 2 km on the smaller Orange River. Stratum IV included the
Caloosahatchee estuary, Matlacha Pass, Pine Island Sound and Estero Bay.


METHODS

Manatee abundance and distribution in the study area were determined
by aerial surveys during January and February, 1984 and 1985. The
winter (1985) that power plant operation was interrupted is referred to
below as the "treatment winter". The movements of 14 manatees were
followed by radio telemetry the treatment winter. Water temperatures were
recorded daily during the first winter and continuously the treatment
winter. Mortality was monitored by routine operation of a salvage network
established for retrieval of manatee carcasses in Florida (O'Shea et al.
1985).


Aerial Surveys

Abundance and distribution of manatees were determined by the unit-
recount survey technique, supplemented by intensive search and extended-
area surveys as described below. The observer remained constant for each
type of survey: unit-recount (J.M.P.), intensive search (J.E.R) and
extended area (R.K.F.). The extended-area survey route covered the largest
area, and the intensive-search route covered the least area, as shown in
Figure 1. Data from the unit-recount technique were used to determine
abundance and distribution, and data from the other techniques were used to
supplement information on distribution.

Details of the unit-recount technique are described in Packard, Siniff
and Cornell (in press). Surveys were flown on each of 3 to 5 days after
cold fronts during the winter. Survey units were recounted five times by
one observer, and two indices were calculated. The total count index was
the sum of all individuals sighted over all units. The sight-resight index
was a jackknife estimate of the number of animals in the study area,
correcting for incomplete visibility by a capture-recapture procedure
available in a computer program (CAPTURE) developed by Otis et al. (1978).
The probability of capture (P-HAT) calculated by the program was used as an
index of visibility, and the standard error as an index of error associated
with each survey.

The procedure for the intensive-search and extended-area techniques
has been described by Irvine (1982). On intensive-search surveys, one
observer counts all manatees in the flight path, circling as long as needed










the mouth of the Orange River. Water levels and flow in this river system
are influenced by tides and by water control structures such as the
Franklin locks on the Caloosahatchee River. Aquatic plants eaten by
manatees are present in shallow portions of the rivers, estuary and bays.

The study area was divided into four strata for the purpose of
allocating effort during aerial surveys (Figure 1). The primary stratum
included the area influenced by the thermal discharge of the power plant.
Stratum II included areas with aquatic vegetation near the power plant and
Stratum III included all other areas within 20 km on the Caloosahatchee
River and within 2 km on the smaller Orange River. Stratum IV included the
Caloosahatchee estuary, Matlacha Pass, Pine Island Sound and Estero Bay.


METHODS

Manatee abundance and distribution in the study area were determined
by aerial surveys during January and February, 1984 and 1985. The
winter (1985) that power plant operation was interrupted is referred to
below as the "treatment winter". The movements of 14 manatees were
followed by radio telemetry the treatment winter. Water temperatures were
recorded daily during the first winter and continuously the treatment
winter. Mortality was monitored by routine operation of a salvage network
established for retrieval of manatee carcasses in Florida (O'Shea et al.
1985).


Aerial Surveys

Abundance and distribution of manatees were determined by the unit-
recount survey technique, supplemented by intensive search and extended-
area surveys as described below. The observer remained constant for each
type of survey: unit-recount (J.M.P.), intensive search (J.E.R) and
extended area (R.K.F.). The extended-area survey route covered the largest
area, and the intensive-search route covered the least area, as shown in
Figure 1. Data from the unit-recount technique were used to determine
abundance and distribution, and data from the other techniques were used to
supplement information on distribution.

Details of the unit-recount technique are described in Packard, Siniff
and Cornell (in press). Surveys were flown on each of 3 to 5 days after
cold fronts during the winter. Survey units were recounted five times by
one observer, and two indices were calculated. The total count index was
the sum of all individuals sighted over all units. The sight-resight index
was a jackknife estimate of the number of animals in the study area,
correcting for incomplete visibility by a capture-recapture procedure
available in a computer program (CAPTURE) developed by Otis et al. (1978).
The probability of capture (P-HAT) calculated by the program was used as an
index of visibility, and the standard error as an index of error associated
with each survey.

The procedure for the intensive-search and extended-area techniques
has been described by Irvine (1982). On intensive-search surveys, one
observer counts all manatees in the flight path, circling as long as needed










to count groups. An additional backseat observer on the opposite side of
the plane reports sightings to the primary observer on extended-area
surveys. Intensive-search surveys were scheduled following passage of
intense and prolonged cold fronts and were augmented by weekly surveys
during the second winter (Reynold and Wilcox, unpub. manus.). Extended-
area surveys were scheduled twice each month as part of a year-long study,
with bias toward flying during warm spells.


Radio Telemetry

Radios were attached to the peduncles of 16 manatees captured in the
power plant discharge canal on 7 Jan. 1985; 14 of the radios were
subsequently relocated sufficiently frequently to yield data on long-term
movements. The floating radio package was attached by a 2-m tether to a
peduncle belt (Rathbun, Reid and Baurassa, pers. commun.). Otherwise,
radio telemetry procedures were similar to those described by Powell and
Rathbun (1984).

Searches for radio-tagged manatees were conducted almost every day
from a boat, plane, or on land. Two individuals were each followed
continuously by boat for 48 hours in February. Aerial searches of the
region outside the study area were made periodically as the manatees
dispersed in February and March.


Environmental Parameters

Tidal stage during surveys, air, and water temperatures were
monitored. Daily maximum and minimum air temperatures were obtained from
the NOAA weather station in Fort Myers. Tidal stage was measured as the
number of hours from the closest low tide at the time of unit-recount
surveys (1000EST). The times of low tides were taken from tide tables for
St. Petersburg, and 2 hr 44 min were subtracted to estimate tidal stage in
the Caloosahatchee River. Water temperatures recorded at 1000EST in the
intake and discharge pipes of the power plant were provided by Florida
Power and Light Company. Gulf water temperatures were recorded daily with
a hand-held thermometer at the Sanibel Island pier during both years.
During 1985, water temperatures at the effluent and Franklin locks were
monitored continuously by automatic recording thermographs anchored at
least 1 m below the water surface at low tide. A thermograph located at
the mouth of Estero Bay was transferred to the mouth of the Orange River on
20 Jan. 1985. The temperature at 1000EST on each day was obtained from the
thermograph records.


Analysis

The possible effects of environmental parameters on survey results
were examined by analysis of variance and nonparametric correlations
(Kendall's tau). A general linear model procedure was used to determine
the effect of year on each of the air and water temperature variables. The
total count was subdivided into counts within three strata on each survey,
and the effects of year, strata and a year by strata interaction on










to count groups. An additional backseat observer on the opposite side of
the plane reports sightings to the primary observer on extended-area
surveys. Intensive-search surveys were scheduled following passage of
intense and prolonged cold fronts and were augmented by weekly surveys
during the second winter (Reynold and Wilcox, unpub. manus.). Extended-
area surveys were scheduled twice each month as part of a year-long study,
with bias toward flying during warm spells.


Radio Telemetry

Radios were attached to the peduncles of 16 manatees captured in the
power plant discharge canal on 7 Jan. 1985; 14 of the radios were
subsequently relocated sufficiently frequently to yield data on long-term
movements. The floating radio package was attached by a 2-m tether to a
peduncle belt (Rathbun, Reid and Baurassa, pers. commun.). Otherwise,
radio telemetry procedures were similar to those described by Powell and
Rathbun (1984).

Searches for radio-tagged manatees were conducted almost every day
from a boat, plane, or on land. Two individuals were each followed
continuously by boat for 48 hours in February. Aerial searches of the
region outside the study area were made periodically as the manatees
dispersed in February and March.


Environmental Parameters

Tidal stage during surveys, air, and water temperatures were
monitored. Daily maximum and minimum air temperatures were obtained from
the NOAA weather station in Fort Myers. Tidal stage was measured as the
number of hours from the closest low tide at the time of unit-recount
surveys (1000EST). The times of low tides were taken from tide tables for
St. Petersburg, and 2 hr 44 min were subtracted to estimate tidal stage in
the Caloosahatchee River. Water temperatures recorded at 1000EST in the
intake and discharge pipes of the power plant were provided by Florida
Power and Light Company. Gulf water temperatures were recorded daily with
a hand-held thermometer at the Sanibel Island pier during both years.
During 1985, water temperatures at the effluent and Franklin locks were
monitored continuously by automatic recording thermographs anchored at
least 1 m below the water surface at low tide. A thermograph located at
the mouth of Estero Bay was transferred to the mouth of the Orange River on
20 Jan. 1985. The temperature at 1000EST on each day was obtained from the
thermograph records.


Analysis

The possible effects of environmental parameters on survey results
were examined by analysis of variance and nonparametric correlations
(Kendall's tau). A general linear model procedure was used to determine
the effect of year on each of the air and water temperature variables. The
total count was subdivided into counts within three strata on each survey,
and the effects of year, strata and a year by strata interaction on










to count groups. An additional backseat observer on the opposite side of
the plane reports sightings to the primary observer on extended-area
surveys. Intensive-search surveys were scheduled following passage of
intense and prolonged cold fronts and were augmented by weekly surveys
during the second winter (Reynold and Wilcox, unpub. manus.). Extended-
area surveys were scheduled twice each month as part of a year-long study,
with bias toward flying during warm spells.


Radio Telemetry

Radios were attached to the peduncles of 16 manatees captured in the
power plant discharge canal on 7 Jan. 1985; 14 of the radios were
subsequently relocated sufficiently frequently to yield data on long-term
movements. The floating radio package was attached by a 2-m tether to a
peduncle belt (Rathbun, Reid and Baurassa, pers. commun.). Otherwise,
radio telemetry procedures were similar to those described by Powell and
Rathbun (1984).

Searches for radio-tagged manatees were conducted almost every day
from a boat, plane, or on land. Two individuals were each followed
continuously by boat for 48 hours in February. Aerial searches of the
region outside the study area were made periodically as the manatees
dispersed in February and March.


Environmental Parameters

Tidal stage during surveys, air, and water temperatures were
monitored. Daily maximum and minimum air temperatures were obtained from
the NOAA weather station in Fort Myers. Tidal stage was measured as the
number of hours from the closest low tide at the time of unit-recount
surveys (1000EST). The times of low tides were taken from tide tables for
St. Petersburg, and 2 hr 44 min were subtracted to estimate tidal stage in
the Caloosahatchee River. Water temperatures recorded at 1000EST in the
intake and discharge pipes of the power plant were provided by Florida
Power and Light Company. Gulf water temperatures were recorded daily with
a hand-held thermometer at the Sanibel Island pier during both years.
During 1985, water temperatures at the effluent and Franklin locks were
monitored continuously by automatic recording thermographs anchored at
least 1 m below the water surface at low tide. A thermograph located at
the mouth of Estero Bay was transferred to the mouth of the Orange River on
20 Jan. 1985. The temperature at 1000EST on each day was obtained from the
thermograph records.


Analysis

The possible effects of environmental parameters on survey results
were examined by analysis of variance and nonparametric correlations
(Kendall's tau). A general linear model procedure was used to determine
the effect of year on each of the air and water temperature variables. The
total count was subdivided into counts within three strata on each survey,
and the effects of year, strata and a year by strata interaction on










manatees per strata were examined. For the treatment winter (1985), the
surveys were classified as to the cold front after which each occurred
(sufficient samples were obtained after 3 out of 4 fronts). For each
stratum, cold front periods were compared using a multiple comparison test
(Student-Newman-Keuls) for differences among mean counts. The data from
both years were pooled for correlations among survey variables (total count
index, sight-resight index, P-HAT, standard error) and environmental
parameters (air minimum, maximum, average, effluent, intake, Gulf, tide).
Correlations were also calculated among the survey variables and
temperature variables recorded only during the treatment winter (Franklin
locks water temperature, difference between the locks and the effluent,
difference between maximum air temperature and the effluent).
Intercorrelations among various temperature variables were examined.
Statistical tests were considered significant at the 0.05 level and were
calculated by a standard computer program (SAS Inst. Inc. 1982).


RESULTS

Overview

Abundance of manatees in the study area did not decline significantly
between the first winter (control) and the winter that discharge of the
heated effluent was interrupted (treatment). However, distribution of
manatees within the study area changed between years, in a pattern related
to water temperature differences of 1 to 6C between areas. While the
heated effluent was not operating, manatees aggregated near the Franklin
locks, a relatively deep body of water that remained warmer longer than the
unheated power plant canal. Many, but not all manatees aggregated at the
heated effluent within three days after it was turned on (21 Jan. to 1 Feb.
1985). At the beginning of the winters, manatees were observed feeding
more frequently in the Caloosahatchee River during the treatment winter
compared to the control winter. Late in the winter, radio-tagged
individuals moved out of the study area to bays where seagrass beds are
located. Cold-related mortality did not increase in the treatment winter.
Results are described more fully below.


Abundance

If manatees had moved to an alternative warm-water refuge outside the
study area, then a reduction in abundance would have been expected between
the control and treatment winters. Detection of a change in abundance is
somewhat complicated, as manatees move in and out of the study area within
winters and visibility changes among surveys (Packard, Siniff and Cornell,
in press). We present the results of the total count and sight-resight
indices below, followed by information on visibility, which is needed to
assess if the results were confounded by a change between years in the bias
of index values.


Total count index

There was no significant difference in the means of total manatee










manatees per strata were examined. For the treatment winter (1985), the
surveys were classified as to the cold front after which each occurred
(sufficient samples were obtained after 3 out of 4 fronts). For each
stratum, cold front periods were compared using a multiple comparison test
(Student-Newman-Keuls) for differences among mean counts. The data from
both years were pooled for correlations among survey variables (total count
index, sight-resight index, P-HAT, standard error) and environmental
parameters (air minimum, maximum, average, effluent, intake, Gulf, tide).
Correlations were also calculated among the survey variables and
temperature variables recorded only during the treatment winter (Franklin
locks water temperature, difference between the locks and the effluent,
difference between maximum air temperature and the effluent).
Intercorrelations among various temperature variables were examined.
Statistical tests were considered significant at the 0.05 level and were
calculated by a standard computer program (SAS Inst. Inc. 1982).


RESULTS

Overview

Abundance of manatees in the study area did not decline significantly
between the first winter (control) and the winter that discharge of the
heated effluent was interrupted (treatment). However, distribution of
manatees within the study area changed between years, in a pattern related
to water temperature differences of 1 to 6C between areas. While the
heated effluent was not operating, manatees aggregated near the Franklin
locks, a relatively deep body of water that remained warmer longer than the
unheated power plant canal. Many, but not all manatees aggregated at the
heated effluent within three days after it was turned on (21 Jan. to 1 Feb.
1985). At the beginning of the winters, manatees were observed feeding
more frequently in the Caloosahatchee River during the treatment winter
compared to the control winter. Late in the winter, radio-tagged
individuals moved out of the study area to bays where seagrass beds are
located. Cold-related mortality did not increase in the treatment winter.
Results are described more fully below.


Abundance

If manatees had moved to an alternative warm-water refuge outside the
study area, then a reduction in abundance would have been expected between
the control and treatment winters. Detection of a change in abundance is
somewhat complicated, as manatees move in and out of the study area within
winters and visibility changes among surveys (Packard, Siniff and Cornell,
in press). We present the results of the total count and sight-resight
indices below, followed by information on visibility, which is needed to
assess if the results were confounded by a change between years in the bias
of index values.


Total count index

There was no significant difference in the means of total manatee










counts (unit-recount surveys) compared across years (Mann Whitney U =
137.7, n = 12, m = 13, a 0.1; Conover 1980). The mean total counts were
130 and 147 manatees for the control and treatment years, respectively.
Values for each survey are listed in Table 1 for the treatment year, and
Table 1 in Packard, Siniff and Cornell (in press) for the control year.
Thirteen of the 15 unit-recount surveys conducted in the treatment year met
the criteria specified by Packard, Siniff and Cornell (in press) for
inclusion in analyses comparing indices between years.

The maximum count from unit-recount surveys was higher in the
treatment winter (range of 80 to 223 manatees) than in the control winter
(97 to 184 manatees). The values of total counts were not significantly
correlated with any of the environmental parameters examined across both
winters. However, total counts were negatively correlated with temperature
at the Franklin Locks during the treatment winter (Kendall's tau = -0.48, p
= 0.02, n = 15).

Substantial changes in total counts between the morning and the
afternoon of the same day were observed (Table 1). For example, on 19 Jan.
1985, 208 manatees were counted in the morning (unit-recount survey) and
338 manatees were counted in the afternoon (intensive search survey). On
29 Jan. 1985, counts were 113 and 230 in the morning and afternoon,
respectively. On four other dates when two surveys were conducted, the
differences between total counts (afternoon minus morning) were 31, 36, -54
and -11 for 10 Jan. 1985, 30 Jan. 1984, 1 Feb. 1984 and 7 Feb. 1984,
respectively. As the sign of the difference changed, we do not believe
changes in counts could be attributed solely to the use of different survey
techniques in the morning and afternoon.


Sight-resight index

Although there were non-overlapping confidence intervals between the
sight-resight index values within the first and last cold fronts of each
winter, the maximum index values occurring after the second cold front did
not differ significantly between years (Figure 2). The maximum estimate of
manatees within the study area during the control winter was 268 (95%
confidence interval of 161 to 375) (Packard, Siniff and Cornell, in press).
During the treatment winter, the maximum estimate was 264 manatees (95%
confidence interval of 247 to 281). There was no significant difference
between years in the means of the sight-resight index (U = 120, n = 11, m =
13, p 0.1).

The sight-resight index values were not significantly correlated with
any of the measured environmental parameters. However, during the
treatment winter, the standard error was significantly correlated with the
difference between maximum air and the effluent temperatures (tau = 0.49, p
= 0.02, n = 14).


Visibility

The sightability of manatees did not change between winters (Table 1,
present study; Table 1, Packard, Siniff and Cornell, in press). An index

















---o 1984
*-* 1985


1 2 3 4 5

FRONT 1 (days)


1 2 3 4 5 1 2 3 4 5


FRONT 2 (days)


Sight-resight index of manatee abundance during the control
winter (open circles) and the treatment winter (solid dots)
compared after each of three cold fronts.


400








300








200 -


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FRONT 3 (days)


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of sightability, the average capture probability (P-HAT), ranged from 0.20
to 0.57 over both winters. The mean sightability for the control winter
(mean P-HAT = 39.5, se = 3.4, n = 11) was similar as for the treatment
winter (mean P-HAT = 38.2, se = 2.2, n = 14). During the treatment winter,
the index of sightability was negatively correlated with the water
temperature at the Franklin locks (tau = -0.57, n = 14, p = 0.01).

The proportion of radio-tagged manatees sighted (those sighted divided
by the number that were in the area) ranged from 0.09 to 0.62 (Table 1).
With data from four additional surveys added, the mean proportion sighted
was low (X = 0.27, n = 17, se = 0.14) relative to another study (Packard,
Summers and Barnes 1985).

The proportion of radio-tagged manatees sighted was relatively high
on two surveys when the total count index was also high. On 24 Jan. 1985,
the total count for the unit-recount survey was 223 manatees and 62% of the
radio-tagged manatees in the area were sighted. On the afternoon of 29
Jan. 1985, the total count for the extended area survey was 230 and 58% of
the radio-tagged manatees in the area were sighted.

Some error in identifying manatees sighted as having transmitters
attached was apparent. On four unit-recount surveys, a back seat observer
recorded two radioed manatees not recorded by the primary observer. The
size and color of the floating transmitter was similar to crab trap buoys
used in the area. On 30 occasions during the 19 surveys, the floating
transmitters on the 2-m tethers were visible but the bodies of the tagged
manatees were not visible. The depth of light penetration was measured
with a Secchi disk as 80 cm in the Orange and Caloosahatchee rivers.

An estimate of sightability was made on the day that the manatees were
captured in the power plant canal. From an airplane, five manatees were
visible in the canal after the net was pulled across the entrance. Twenty
two individuals were released across the net, and an unknown number may
have remained in the canal. Thus, at most, 23% of the manatees present
were sighted from the air on this occasion.

Distribution within the Study Area

The distribution of manatees among strata differed between years, as
indicated by a significant year by strata interaction in the analysis of
variance in the counts from unit-recount surveys (SS = 5435.3, df = 2, F =
3.53, p = 0.035). The effect of strata contributed more to the variance
(SS = 82685.8, df = 2, F = 53.73, p = 0.0001) than the effect of year (SS =
550.6, df = 1, F = 0.72, p = 0.4).

The change in distribution was primarily in the second and third
strata, rather than the primary stratum (Figure 3). Within the data
partitioned by strata, year had a significant effect (p 0.05) on variance
in counts for strata II and III but not for stratum I. In contrast to the
control winter, manatees in strata II and III were observed resting at the
Franklin locks, feeding and traveling in the upper Caloosahatchee and upper
Orange rivers during the treatment winter. Distribution changed within
stratum I relative to operation of the power plant. The mean count was

















120







80


I 11*


III*


Strata






Figure 3. Distribution of manatees among three strata during the control
(white) and treatment (shaded) winters. Means differed
significantly between winters in the strata marked with an
asterisk.









significantly higher after the fourth front compared to the first and
second fronts when the effluent was not heated. In the other two strata,
mean counts differed significantly after the second and fourth fronts, but
were similar at the beginning and end of the period. Some manatees
gathered near the unheated effluent after the first front; thus fewer were
in the Caloosahatchee River at the beginning and end of the winter than in
the middle of the winter.


Behavior Relative to Temperature

Water temperatures monitored during the treatment winter varied by as
much as 6C at the four sites. Bay water temperatures were lower than the
river sites throughout the winter. The temperature of the unheated
effluent dropped below the water temperature at the Franklin locks during
the first front, and remained lower until 21 Jan. 1985 when the effluent
was heated at the beginning of the third front (Figure 4a). Water at the
Franklin locks was warmer than at the mouth of the Orange River until 23
Jan.

Shifts in manatee distribution between the Franklin locks and power
plant appeared to be related to a behavioral response at a temperature
threshold of about 18C (Figure 4b). Prior to the second front, more
manatees were in the Orange River (many outside the power plant canal) than
the Caloosahatchee River, when the temperature at both the locks and the
effluent canal was above 18C (as measured at 1000EST). The effluent canal
cooled to 17C during the second front, and the manatees shifted to the
Caloosahatchee River. The locks remained at 18C or above until the end of
the third front, at which time manatee distribution began to shift back to
the Orange River and the heated effluent.

Temperature at the mouth of the Orange River remained near or below
18C until 2 days after the fourth front, meaning that manatees attracted to
the power plant within days after it was turned on would have been
travelling in waters below the presumed threshold while moving from the
locks to the power plant. Distribution of radio-tagged manatees was fairly
evenly split between the locks and power plant after the third front, and
most of the animals did not switch to the power plant until after the
fourth front (Figure 4c).

A strict relationship between distribution and a threshold of 18C is
not so apparent after the fourth front. More manatees were sighted on a
unit-recount survey in the Caloosahatchee than the Orange River on 28 Jan.
(one day after the fourth front), when both the locks and mouth of the
Orange River were below 18C. On 28 Jan., there was only 0.5C difference
between the mouth of the Orange River and the Franklin locks; subsequently
these two sites differed by 2-4C. Orange River manatee counts were
subsequently higher, even when the Franklin locks had warmed to 18C (2
Feb.). Thus it appears that toward the end of the winter, manatee
distribution was affected by the temperature differential, possibly
overriding sensitivity to a temperature threshold.











- 24

L.
y 20
0
a,


It
I 20






C. is

10


5 10 15 20 25 30
January


Figure 4. Comparison during the treatment winter of (a) maximum and minimum
water temperatures at the Franklin locks (white) and power plant
effluent (shaded), (b) percentage of total manatees counted on
aerial survey, as located at the Franklin locks (white) and power
plant (shaded), and (c) number of radio-tagged manatees located
at the locks (white) and power plant (shaded). Horizontal bars
on the x-axis indicate cold fronts. The vertical line marks the
date that the power plant was turned on.










The control and treatment winters did not differ significantly in mean
temperatures, but did differ in temperature extremes. Year had no
significant effect on the variance of the mean, maximum or minimum air
temperatures, or on Gulf water temperature. However, the mean air
temperature dropped below 10C on three days (third front) during the
treatment but not the control winter. At this time, Gulf water temperature
was at or below 16C for one week.


Movements Relative to Feeding Areas.

During the treatment winter, manatees appeared to feed near the warm-
water sites prior to and during discharge of the warm effluent, and to
disperse to the bays after the heated effluent and cold weather ceased, as
indicated by locations of the radio-tagged manatees (Figure 5). However,
the movements of tagged individuals varied enough that it was difficult to
detect what effect, if any, the operation of the power plant had on
movement relative to feeding sites.

Data indicating movement to feeding areas during the control winter
were largely inferential. Aerial counts were low during the warm spells
between cold fronts, possibly explained by manatee movement out of the
unit-recount survey area. On several dates, high counts were obtained 2-5
days after a cold front, when manatees were distributed throughout the
Caloosahatchee River (Packard, Siniff and Cornell, in press). On these
occasions, many manatees were traveling downstream from the power plant and
several groups were observed feeding in the Caloosahatchee downstream from
the Orange River. No manatees were sighted outside the unit-recount survey
area on a survey after the first front. However, after the second front,
on 27 Jan. 1984, seven manatees were sighted in the bays and estuary at the
mouth of the Caloosahatchee River.

During the treatment winter, most of the radio-tagged manatees
remained near the warm-water sites during January (Figure 5). After the
fourth cold front, they left the Orange River and Franklin locks, and were
located in the bays. During a fifth cold front in February, most of the
radio-tagged manatees returned to the warm-water sites. Subsequently, they
dispersed from the Caloosahatchee, some moving as far north as Charlotte
Harbor.

The movements of individual manatees varied in the amount of time
spent near each warm-water site, and in the frequency of movement away from
the site. For example, a pregnant female (Fll) and a female (F3) with a
calf remained near the lock until after the second front, were located in
the upper Caloosahatchee prior to the third front, returned to the lock,
then moved to the Orange River after the third front. A large male (M9)
moved between the Orange River and the upper Caloosahatchee during January,
and was only located at the lock on one occasion. In contrast, another
male (Ml) was located only at the lock during January. Other individuals
(M7, M12) moved occasionally from the lock to the Orange River, such that
they could have sensed if and when the warm effluent was restored.




































o
A^


OPi%


Number of radio-tagged manatees located during the treatment
winter near the Franklin locks (FL), Orange River (OR), upper
Caloosahatchee River (UC), mid Caloosahatchee River (CR), lower
Caloosahatchee River (LC), San Carlos Bay (SC), Matlacha Pass
(MP), Pine Island Sound including Tarpon Bay (PI), Charlotte
Harbor (CH), Peace River (PR) and other points to the north of
Pine Island (OT). The points are arranged left to right in order
of distance from the warm water sites (FL and OR), but the
distance between points is not represented to scale. Dates that
the power plant was operating are indicated by bars.


Figure 5.


o









Manatees were observed feeding in the upper Caloosahatchee River
during aerial surveys and tracking sessions during January of the treatment
winter. This was in contrast to aerial observations during the control
winter, when manatees were rarely seen feeding in the upper Caloosahatchee
River, although they did feed in the lower part of the river. Beds of
eelgrass (Valisneria spp.) were visible from the air along the shore and
shallows of the lower Caloosahatchee, but very little submerged vegetation
was seen in the upper Caloosahatchee and Orange rivers. By the end of the
treatment winter, floating and bank vegetation downstream from the lock was
noticeably less abundant compared to the upstream side. The possible
effect of manatee grazing on the downstream side may have been complicated
by other factors such as salinity and herbicide treatment.

The movements of two manatees tracked for 48 hrs on two occasions
after the fourth front illustrated how some individuals might be inhibited
from moving long distances from the Orange River due to water temperature
gradients. On 30 Jan., the adult female (F3) left the Orange River (22C)
and traveled down the Caloosahatchee River to the Hwy 41 bridge where the
water was 18.5C. She returned to the Orange River within 12 hrs. Two
hours later, she traveled for 7 hrs downstream to the same general area
(19.5C), returning upstream to slightly warmer water (20C) by the evening.

On 2 Feb., the male manatee M1 left the Orange River (25C), and within
16 hrs had traveled 40km to Matlacha Pass (18-20C) where he was observed
feeding. The water temperature measured in several locations along his
travel route was at or above the presumed threshold of 18C.


Mortality

Cold-stress mortality did not differ between the control and treatment
winters (XI = 0.033, df = 1, p 0.1). During the control winter, 18
manatee carcasses were collected in southwest Florida (Lee, Collier, and
Charlotte counties), of which six deaths were attributed to cold stress (R.
K. Frohlich, unpub. data). During the treatment winter, 10 manatee
carcasses were collected in southwest Florida, of which three deaths were
attributed to cold stress. There was no substantial change in the spatial
distribution of cold stress deaths between the two winters. One such death
occurred within a few km of the heated effluent during the treatment
winter.


DISCUSSION

The results of this study indicated that manatees did not abandon the
Fort Myers area when operation of the heated effluent was interrupted.
Their movements and distribution indicated a sensitivity and thermal taxis
with respect to water temperature gradients of a few degrees C. There was
no indication of a change in movement to feeding sites out of the study
area during the treatment winter; however, distribution of feeding manatees
sighted on unit-recount surveys changed between winters. Manatees were
apparently not exposed to the cold stress that would result in increased
mortal ity.









Manatees were observed feeding in the upper Caloosahatchee River
during aerial surveys and tracking sessions during January of the treatment
winter. This was in contrast to aerial observations during the control
winter, when manatees were rarely seen feeding in the upper Caloosahatchee
River, although they did feed in the lower part of the river. Beds of
eelgrass (Valisneria spp.) were visible from the air along the shore and
shallows of the lower Caloosahatchee, but very little submerged vegetation
was seen in the upper Caloosahatchee and Orange rivers. By the end of the
treatment winter, floating and bank vegetation downstream from the lock was
noticeably less abundant compared to the upstream side. The possible
effect of manatee grazing on the downstream side may have been complicated
by other factors such as salinity and herbicide treatment.

The movements of two manatees tracked for 48 hrs on two occasions
after the fourth front illustrated how some individuals might be inhibited
from moving long distances from the Orange River due to water temperature
gradients. On 30 Jan., the adult female (F3) left the Orange River (22C)
and traveled down the Caloosahatchee River to the Hwy 41 bridge where the
water was 18.5C. She returned to the Orange River within 12 hrs. Two
hours later, she traveled for 7 hrs downstream to the same general area
(19.5C), returning upstream to slightly warmer water (20C) by the evening.

On 2 Feb., the male manatee M1 left the Orange River (25C), and within
16 hrs had traveled 40km to Matlacha Pass (18-20C) where he was observed
feeding. The water temperature measured in several locations along his
travel route was at or above the presumed threshold of 18C.


Mortality

Cold-stress mortality did not differ between the control and treatment
winters (XI = 0.033, df = 1, p 0.1). During the control winter, 18
manatee carcasses were collected in southwest Florida (Lee, Collier, and
Charlotte counties), of which six deaths were attributed to cold stress (R.
K. Frohlich, unpub. data). During the treatment winter, 10 manatee
carcasses were collected in southwest Florida, of which three deaths were
attributed to cold stress. There was no substantial change in the spatial
distribution of cold stress deaths between the two winters. One such death
occurred within a few km of the heated effluent during the treatment
winter.


DISCUSSION

The results of this study indicated that manatees did not abandon the
Fort Myers area when operation of the heated effluent was interrupted.
Their movements and distribution indicated a sensitivity and thermal taxis
with respect to water temperature gradients of a few degrees C. There was
no indication of a change in movement to feeding sites out of the study
area during the treatment winter; however, distribution of feeding manatees
sighted on unit-recount surveys changed between winters. Manatees were
apparently not exposed to the cold stress that would result in increased
mortal ity.










We interpret these findings as indicating that manatees were dependent
on a source of warm water in the Fort Myers area, in that they apparently
had no other reliable source to which they might have moved. However,
whether they need the warm water to survive or are merely attracted to it
remains an open question. Certainly some individuals survived the winter
without detectable movement to the warmest sites. Their condition at the
end of the winter was not known, nor is it known whether the majority of
the population would have shown the same degree of endurance if the heated
effluent had not been restored.

Although we can with certainty conclude that there was not a
significant reduction in mean manatee abundance in the survey area during
the treatment year, we are reluctant to interpret the higher maximum total
counts in the treatment year as indicating an increase in abundance. When
counts were corrected for visibility via the Jackknife procedure, there was
no significant differences in mean counts between years.

The most likely explanation for the higher total counts in the
treatment winter was a change in visibility. Although the mean index of
sightability did not change between years, the percentage of radio-tagged
manatees sighted did vary among surveys and was high on two surveys when
high total counts were obtained. We received the distinct impression that
manatees were basking at the surface in the warm sun when high counts were
obtained. Whether they are more likely to show such thermoregulatory
behavior after a period of heat deprivation (ie. while the effluent was
not heated) remains to be determined.

We cannot completely rule out the possibility that a difference in
weather patterns between the two years may have influenced the bias in the
aerial survey indices, as the third cold front in the treatment year was
more severe than any during the control year. However, we could not detect
any differences between years in the mean air and water temperatures.
Differences in the weather patterns may account for the significant
differences between years in the sight-resight index as compared after the
first and second cold fronts.

The lack of heated effluent at the beginning of the winter was not
critical, because the manatees found an area of water at the Franklin locks
which remained near or above 18C. The severity of the third cold front in
the treatment year would have exposed manatees to about 10 days of river
water temperatures below 18C, had the heated effluent not been restored at
that time. Possibly due to the timing of this action, mortality due to
cold stress did not increase during the winter that the power plant
operation was interrupted. We could not determine whether the manatees
that did not return to the power plant were behaviorally impaired due to
cold stress, hence not functioning in an optimal manner, or were not
stressed.

Movements of the manatees relative to water temperature indicated that
they are capable of discriminating slight differences, and are likely to
abandon sites that drop below 18C. Such sensitivity and behavioral
responses would suggest that behavioral thermoregulation is important, and
that attraction to warm water is critical for maintaining homeostasis, not
just a preference. However, many factors apparently influence their









movements, including possibly a response to temperature differentials as
well as threshold, health, body condition and mass, accommodation, prior
experience, and individual differences in metabolic activity.

The effect of prior experience is suggested by the number of manatees
gathered at the unheated effluent site after the first front, when other
sites were warmer. Manatees appear to be quite traditional in their
movements, certain individuals and their offspring returning to the same
sites year after year (Hartman 1979, Powell and Rathbun 1984). However,
when confronted with changes at the Fort Myers power plant, most of the
manatees also were quite opportunistic in locating and moving to warm sites
in the general area within a matter of days.

Such behavioral flexibility may have been very important prior to the
establishment of industrial warm-water sources. Sites within a water
system apparently vary in temperature due to a number of factors such as
volume of water, current, tide, turbidity and bottom contour. Learned
responses would influence manatees to return to general areas that had been
favorable in the past, and searching patterns combined with thermotaxis
would allow them to identify optimal sites within a dynamic pattern of
warming and cooling bodies of water.

Manatee habitat around the coast of Florida has been substantially
altered to the point that a return of manatees to pre-industrial winter
behavior patterns is no longer probable, and if forced, is unlikely to
support as viable a population. Power plants such as the one in Fort Myers
have an operating life span of about 30 yrs. Economic considerations can
cause plants to be retired early or used intermittently. Where manatees
have become dependent on artificial warm-water sources for thermoregulation
during the winter, cessation of power plant operation could have
substantial effects on survival during severe winters and subsequently on
recovery of the population. Interrupted operation of plants apparently
influences distribution and movements of manatees, with possible negative
implications for the precision of techniques under development to monitor
trends in abundance at winter refuges. This complex management issue must
be addressed if recovery of the endangered manatee population in Florida is
to be insured.


SUMMARY

Manatees appear to be dependent on artificial thermal refuges during
winter in much of Florida, yet little is known about their behavior in the
absence of this beneficial effect of industrial effluents. The abundance
and distribution of manatees in the Caloosahatchee River system was
determined in the winters prior to and during a temporary shut-down of the
heated effluent at the power plant in Fort Myers. Aerial surveys were
conducted both winters, augmented by radio-telemetry during the second
winter. Manatee abundance did not change significantly between winters, as
measured by two indices. Distribution among three habitat strata changed
significantly. When the effluent was not heated, manatees gathered in an
area of deep water that cooled more slowly than river and bay water.
Indirect evidence indicated that most manatees moved from waters below 18C
when warmer water was available; however, some individuals remained in









relatively colder areas even when the heated effluent was restored.
Mortality was not significantly higher than expected during the winter that
the thermal discharge was interrupted. The heated effluent provided a
refuge when Gulf waters dropped below 16C for one week. Without
restoration of the heated effluent, manatees would have been exposed to
prolonged cold below their apparent threshold of tolerance.


ACKNOWLEDGMENTS


The study primarily was funded by Cooperative Agreement No. 14-16-
0009-1544, Research Work Order No. 2, between the U. S. Fish and Wildlife
Service and the Florida Cooperative Fish and Wildlife Research Unit, School
of Forest Resources and Conservation, Institute of Food and Agricultural
Sciences, University of Florida. In the second year, the work was
subcontracted to Texas Agricultural Experiment Station, Texas A&M
University. Funds for associated projects contributing information were
provided by the U. S. Fish and Wildlife Service, the U.S. Marine Mammal
Commission and Florida Power and Light Co. We appreciate the cooperation
of the J. N. "Ding" Darling National Wildlife Refuge staff; the support of
R. Hight and K. Seaman added considerably to the success of the project.
The cooperation of Ft. Myers Airways, including pilots L Little, E.
Wilson, R. Swanson and E.M. Sauls was also greatly appreciated. We are
grateful to the following employees and affiliates of the U.S. Fish and
Wildlife Service Sirenia Project for their dedicated assistance with field
work and necropsies: L. W. Lefebvre, T. J. O'Shea, J. P. Reid, and A.
Wolfe. We thank M. A Clemans for field assistance in all aspects of the
project and C. C. Farquhar, L. K. Giffen, and L S. Procarione for help
with preparation of the manuscript.










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