• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 List of Figures
 List of Tables
 Acknowledgement
 Introduction
 Study areas
 Methods
 Results
 Discussion
 Management recommendations
 Literature cited






Group Title: Florida Cooperative Fish and Wildlife Research Unit Technical report no. 6-2
Title: Aerial census of manatees and boats over the lower St. Johns River and the Intracoastal Waterway in northeastern Florida
CITATION PAGE IMAGE ZOOMABLE
Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00073786/00001
 Material Information
Title: Aerial census of manatees and boats over the lower St. Johns River and the Intracoastal Waterway in northeastern Florida
Series Title: Site-specific reduction of manatee boatbarge mortality report
Physical Description: iv, 55 leaves : ill., maps ; 28 cm.
Language: English
Creator: Kinnaird, M
Florida Cooperative Fish and Wildlife Research Unit
U.S.Fish and Wildlife Service
Publisher: Florida Cooperative Fish and Wildlife Research Unit, U.S. Fish and Wildlife Service
Place of Publication: Gainesville FL
Publication Date: [1983]
 Subjects
Subject: Manatees -- Florida   ( lcsh )
West Indian manatee -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 53-55).
Statement of Responsibility: Margaret F. Kinnaird.
General Note: "Prepared for U.S. Fish and Wildlife Service."
General Note: "October 1983."
General Note: "Cooperative agreement no. 14-16-0004-81-923."
General Note: "Florida Cooperative Fish and Wildlife Research Unit U.S. Fish and Wildlife Service" -- Cover.
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: UF00073786
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 - 001891645
oclc - 28321572
notis - AJW6874

Table of Contents
    Title Page
        Title page
    Table of Contents
        i
    List of Figures
        ii
    List of Tables
        iii
    Acknowledgement
        iv
    Introduction
        Page 1
    Study areas
        Page 2
        Lower St. Johns River
            Page 2
            Page 3
        Intracoastal waterways
            Page 4
    Methods
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
    Results
        Page 9
        Lower St. Johns River
            Page 9
            Manatee abundance
                Page 9
            Manatee distribution in the study area
                Page 9
                Page 10
                Page 11
                Page 12
                Page 13
                Page 14
                Page 15
            Manatee movements and behavioral patterns
                Page 16
                Page 17
                Page 18
                Page 19
            Boat traffic
                Page 20
                Page 21
                Page 22
                Page 23
                Page 24
        Intracoastal waterway
            Page 25
            Manatee abundance
                Page 25
            Manatee distribution in the study area
                Page 25
                Page 26
                Page 27
                Page 28
                Page 29
                Page 30
                Page 31
                Page 32
                Page 33
            Manatee movements and behavioral patterns
                Page 34
            Boat traffic
                Page 34
                Page 35
                Page 36
                Page 37
                Page 38
                Page 39
    Discussion
        Page 40
        Lower St. Johns River
            Page 40
            Page 41
            Page 42
            Page 43
            Page 44
            Page 45
            Page 46
        Intracoastal waterway
            Page 47
            Page 48
            Page 49
            Page 50
    Management recommendations
        Page 51
        Page 52
    Literature cited
        Page 53
        Page 54
        Page 55
Full Text















Aerial Census of Manatees
and Boats over the Lower St. Johns River
and the Intracoastal Waterway
in Northeastern Florida




October 1983



Margaret F. Kinnaird

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




Prepared for:

U.S. Fish and Wildlife Service
75 Spring Street, S.W.
Atlanta, GA 30303







Cooperative Agreement No. 14-16-0004-81-923

Site-Specific Reduction of Manatee Boat/Barge Mortality Report No. 2











Table of Contents

Page

List of Figures ii

List of Tables iii

Acknowledgements iv

Introduction 1

Study Areas 2

Lower St. Johns River 2
Intracoastal Waterway 4

Methods 4

Results 9

Lower St. Johns River 9

Manatee abundance 9
Manatee distribution in the study area 9
Manatee movements and behavioral patterns 16
Boat traffic 20

Intracoastal Waterway 25

Manatee abundance 25
Manatee distribution in the study area 25
Manatee movements and behavioral patterns 34
Boat traffic 34

Discussion 40

Lower St. Johns River 40
Intracoastal Waterway 47

Management Recommendations 51

Literature Cited 53










List of Figures

FIGURE PAGE

1. St. Johns River study area 3

2. Intracoastal Waterway study area 5

3. Flight path over the St. Johns River 7

4. Flight path over the Intracoastal Waterway 8

5. Number of manatees counted by month and quarter of the
year in the St. Johns River 10

6. Frequency of group size in the St. Johns River 12

7. Relationship between temperature and manatee counts in the
St. Johns River 13

8. Number of manatees counted in ten zones of the St. Johns River 14

9. Seasonal distribution of manatees in the St. Johns River 17.

10. Activity of manatees in the St. Johns River 18

11. Number of boats counted by month and quarter of the year
in the St. Johns River 21
12. Distribution of four boat classes in the St. Johns River 24

13. Number of manatees counted by month and quarter of the year
in the Intracoastal Waterway 26

14. Frequency of group size in the Intracoastal Waterway 28

15. Relationship between temperature and manatee counts in the
Intracoastal Waterway 29

16. Number of manatees counted in eight zones of the Intracoastal
Waterway 30

17. Seasonal distribution of manatees in the Intracoastal Waterway 32

18. Activity of manatees in the Intracoastal Waterway 37
19. Number of boats counted by month and quarter of the year in
the Intracoastal Waterway 38
20. Distribution of four boat classes in the Intracoastal
Waterway 43










List of Tables
TABLE PAGE

1. Numbers and ratios of adults and calves sighted in the St. Johns
River 11

2. Density of manatees in ten zones of the St. Johns River 15

3. Seasonal frequency of manatee activity in the St. Johns River 19

4. Seasonal abundance of six boat classes in the St. Johns River 22

5. Density of six boat classes in ten zones of the St. Johns River 23

6. Numbers and ratios of calves and adults sighted in the Intracoastal
Waterway 27

7. Density of manatees in eight zones of the Intracoastal Waterway 33

8. Seasonal frequency of manatee activity in the Intracoastal
Waterway 35

9. Seasonal abundance of six boat classes in the Intracoastal
Waterway 39

10. Density of six boat classes in eight zones in the Intracoastal
Waterway 41











Acknowledgements

This study was funded by a U.S. Fish and Wildlife Service contract to
the Florida Cooperative Fish and Wildlife Research Unit and the University of
Florida. Support was provided by the School of Forest Resources and
Conservation at the University of Florida.

I am especially grateful to Drs. D. Jenkins and M. Clarkson of the Dept.
of Aerospace and Engineering, Univ. of FL., for allowing me the continued use
of their airplane. My pilot, W. Fisher, deserves special thanks for his
masterful flying and ability to keep us all well entertained. I am indebted
to M. Leadon and particularly R. Mulholland who bore the cold, held their
stomachs and meticulously counted boats. B. Newmark, F. Lund, J. Nettles, B.
Wallace, S. Chestnut and T. O'Shea also participated in several flights.

G. Rathbun and T. O'Shea advised during the initial stages of the
project and offered continued support. R. Mulholland skillfully processed
much of the data, J. Lottinville drew the figures and D. Stinson typed the
report. T. O'Shea, D. Peterson, D. Laist and R. Gregory reviewed and
commented on previous drafts of the report.

Above all, I offer special thanks to J. Powell who trained me as an
aerial surveyor and developed my eye for spotting manatees some eight years
ago.











INTRODUCTION


West Indian manatees (Trichechus manatus) occur throughout the year in
rivers, estuaries and coastal areas of Florida (Moore 1951, Hartman 1974,
Irvine and Campbell 1978, Irvine et al. 1981). Manatees are widely dispersed
along the Gulf and Atlantic Coasts of the southeastern U.S. during the summer
months and aggregate at traditional warm water wintering sites during cooler
months (Hartman 1974, Powell and Waldron 1978, Rose and McCutcheon 1980,
Rathbun et al. 1982, Powell and Rathbun 1983, Shane 1983). Their winter
range on the east coast of Florida extends as far north as Jacksonville
(Hartman 1974, Rathbun et al. 1983, Kinnaird and Valade 1983) but manatees
are sighted most frequently in the northeastern region of the peninsula
during the summer months (Moore 1951, Hartman 1974, Irvine and Campbell
1978). Recent evidence suggests that manatees in northeastern Florida are
not discrete subpopulations and that manatees make seasonal north/south
migrations along the eastern coastal waterways (Hartman 1974, Shane 1983,
Rathbun et al. 1983, Kinnaird and Valade 1983).
Northeastern Florida has the highest known manatee mortality in the
state, including the highest incidence of deaths due to collisions with
boats, particularly in the St. Johns River and Brevard County (O'Shea et al.
in prep.). It is difficult to develop wise management policies for this
region because spatial and temporal use of northeastern Florida by manatees
has not been fully documented. The nature and extent of boat traffic also
has not been described.
Partial surveys of manatees in northeastern Florida have been conducted
by Hartman (1979), Irvine and Campbell (1978) and Rose and McCutcheon (1980).
All of the studies were seasonal and surveys were not conducted throughout
one entire year. Seasonal changes in local distribution and abundance in
northeastern Florida havebeen documented only for Brevard County (Shane
1983) and the upper St. Johns River (Bengston 1982).
Aerial surveys are the only cost-effective means to census marine
mammals over large areas (Irvine et al. 1981). However, counts from aerial
surveys must be viewed with caution because the number of animals undetected
during a survey is never known (Hartman 1974, Irvine and Campbell 1978).
Also, variability between surveys is high, and ground-truthing techniques
have not been refined (Packard et al. 1983). Results of aerial surveys are
therefore only an index of abundance at the time of the survey, but these
counts are useful to document distribution, relative abundance, and patterns
of habitat use (Irvine et al. 1981).
I conducted aerial surveys for one complete year over the lower reaches
of the St. Johns River and the northeastern section of the ICW (southern
Volusia County to Kings Bay, Georgia) to document the spatial and temporal
patterns that characterize manatee use of northeast Florida, and to describe
the nature and extent of boat traffic. The development of management
practices based on these patterns should help minimize resource conflicts and
possibly reduce manatee boat/barge mortality.











STUDY AREAS

Lower St. Johns River
The study area incorporates the lower 78 kilometers of the St. Johns
River, including major tributaries (Fig. 1). The southern border of the
study area is delineated by the Shands Bridge in the city of Green Cove
Springs, approximately 230 kilometers north of Blue Spring. The northern
border lies at the confluence of the St. Johns River and the Atlantic Ocean.
The study area was divided, for the purpose of data analysis, into ten
arbitrary zones, delineated by bridges and other geographical features
recognizable during low level flights.
The northern two-thirds of the study area (zones 1-7) fall under the
jurisdiction of Duval County. The southern one-third (zones 8-10) is divided
by St. Johns County to the east and Clay County to the west.
The St. Johns flows in a northward direction until the river bisects the
heavily industrialized riverfront city of Jacksonville, where it turns east
(zone 3) and flows towards the coast. Two additional cities, Orange Park and
Green Cove Springs, are located on the western shore of the St. Johns River.
Mayport US Naval Air Station is located at the mouth of the river on the
southern bank. The St. Johns River is bisected by the ICW approximately five
kilometers west of Mayport.

The Port of Jacksonville, located in the heart of the city of
Jacksonville, is the largest and most active shipping port along the Atlantic
coast south of Hatteras, NC (Jacksonville Port Handbook 1981/82). During
1980 alone, approximately 17,000 vessel trips were logged in Jacksonville
Harbor (U.S. Army Corps of Engineers).
Water depth in the study area varies from 24 meters in the dredged
ship-channels north of the Fuller-Warren bridge (zones 1, 2, 3, & 5) to one
meter in major tributaries and associated lakes (zones 4, 7 & 9-10). Mean
tidal range is 1.22 m (Southern Waterway Guide, Inc. 1983). Water currents
average approximately 5.5 km/hr near the mouth of th& river, increasing up to
9.3 km/hr where the river narrows at the city bridges (zone 5) and decreasing
to less than 2 km/hr south of the bridges (Southern Waterway Guide 1983).
Water clarity is extremely poor throughout the study area and decreases
dramatically north of the Fuller Warren Bridge in the industrialized section
of the river (zones 1-7). A zone of transition between seawater and river
water extends upstream from Jacksonville but chloride concentrations begin to
weaken south of zone five (Anderson and Goolsby 1973).
Submerged aquatic vegetation, consisting primarily of sparse beds of
eelgrass (Vallisneria americana), is found on the east and west banks
south of the Buckman Bridge (zone 8) and throughout Doctor's Lake (zone 10).
Little aquatic vegetation other than floating mats of water hyacinth
(Eichhornia crassipes) and cordgrass (Spartina bakeri) is present north of the
Buckman Bridge.











STUDY AREAS

Lower St. Johns River
The study area incorporates the lower 78 kilometers of the St. Johns
River, including major tributaries (Fig. 1). The southern border of the
study area is delineated by the Shands Bridge in the city of Green Cove
Springs, approximately 230 kilometers north of Blue Spring. The northern
border lies at the confluence of the St. Johns River and the Atlantic Ocean.
The study area was divided, for the purpose of data analysis, into ten
arbitrary zones, delineated by bridges and other geographical features
recognizable during low level flights.
The northern two-thirds of the study area (zones 1-7) fall under the
jurisdiction of Duval County. The southern one-third (zones 8-10) is divided
by St. Johns County to the east and Clay County to the west.
The St. Johns flows in a northward direction until the river bisects the
heavily industrialized riverfront city of Jacksonville, where it turns east
(zone 3) and flows towards the coast. Two additional cities, Orange Park and
Green Cove Springs, are located on the western shore of the St. Johns River.
Mayport US Naval Air Station is located at the mouth of the river on the
southern bank. The St. Johns River is bisected by the ICW approximately five
kilometers west of Mayport.

The Port of Jacksonville, located in the heart of the city of
Jacksonville, is the largest and most active shipping port along the Atlantic
coast south of Hatteras, NC (Jacksonville Port Handbook 1981/82). During
1980 alone, approximately 17,000 vessel trips were logged in Jacksonville
Harbor (U.S. Army Corps of Engineers).
Water depth in the study area varies from 24 meters in the dredged
ship-channels north of the Fuller-Warren bridge (zones 1, 2, 3, & 5) to one
meter in major tributaries and associated lakes (zones 4, 7 & 9-10). Mean
tidal range is 1.22 m (Southern Waterway Guide, Inc. 1983). Water currents
average approximately 5.5 km/hr near the mouth of th& river, increasing up to
9.3 km/hr where the river narrows at the city bridges (zone 5) and decreasing
to less than 2 km/hr south of the bridges (Southern Waterway Guide 1983).
Water clarity is extremely poor throughout the study area and decreases
dramatically north of the Fuller Warren Bridge in the industrialized section
of the river (zones 1-7). A zone of transition between seawater and river
water extends upstream from Jacksonville but chloride concentrations begin to
weaken south of zone five (Anderson and Goolsby 1973).
Submerged aquatic vegetation, consisting primarily of sparse beds of
eelgrass (Vallisneria americana), is found on the east and west banks
south of the Buckman Bridge (zone 8) and throughout Doctor's Lake (zone 10).
Little aquatic vegetation other than floating mats of water hyacinth
(Eichhornia crassipes) and cordgrass (Spartina bakeri) is present north of the
Buckman Bridge.










Figure 1. St. Johns River study area.


Jacksonville


I I -.
3 m





9

3t. Johns Co.


Green Cove











Several artificial warm water sources are present within the study area:
the Alton Packing Corp. (APC) and the Jacksonville Electric Authority's (JEA)
J. D. Kennedy (KGS), Southside (SGS) and Northside Generating Stations (NGS).

Intracoastal Waterway (ICW)
This study area includes a 263 kilometer stretch of the ICW extending
from just north of Kings Bay, Georgia, south to Oak Hill, Florida (Fig. 2).
The mainland borders the ICW on the west; barrier islands to the east
separate the waterway from the Atlantic Ocean. Three inlets and the mouths
of three rivers link this stretch of the ICW to the Atlantic Ocean.
The study area was divided into eight arbitrary zones for the purpose of
data analysis. These zones are 20 to 40 kilometers in length, delineated by
bridges and other geographical landmarks recognizable during low level
flights.

This region includes many communities on both banks of the ICW. Major
communities are: Fernandina Beach, Jacksonville Beach, St. Augustine, Ormond
Beach, Daytona Beach and New Smyrna Beach. Tomoka and Anastasia State Parks,
Matanzas National Monument, and Cumberland Island National Seashore are
located within the study area.
The ICW is used by commercial vessels and tows unable to navigate long
stretches in the open ocean, and by pleasure craft. Small boat and
recreational facilities are found throughout the northeast section of the
waterway (NOAA 1982).
With the exception of the Fernandina and Daytona Beach areas (zones 1
and 7), the waterway is generally narrow, sheltered, protected from strong
winds and usually free of rough water. Depths of 3.6 m are reported
throughout the length of the waterway but significant shoaling and shifting
occurs, particularly around inlets and river mouths. Currents up to 7.4
km/hr may be encountered. Mean tidal ranges vary from 2 m at Fernandina
Beach (zone 1) to less than 1 m at Ponce de Leon Inlet (zone 8) (Southern
Waterway Guide 1983). Habitat varies from salt marsh'(zones 1 and 2) to
subtropical mangrove estuaries (zone 8). Waters are turbid and generally
void of aquatic vegetation with the exception of inlets and the southern
extremes of the study area (zones 7 and 8).

Three pulp mills and one generating station are located within the study
area: Container Corporation of America, Fernandina Beach, FL; ITT Rayonier
Mill, Fernandina Beach, FL; Gillman Paper Co., St. Marys, Georgia; and New
Smyrna Utilities, Ponce de Leon, FL. All of the these companies discharge
warm water into the ICW. The Ponce de Leon generating plant is presently
being phased out and was not operating during the course of this study.

METHODS
Aerial surveys were flown over both study areas between 8 July 1982 and
16 June 1983. Surveys were conducted twice monthly for each study area;
generally once during the week and once over the weekend. Only one survey











Several artificial warm water sources are present within the study area:
the Alton Packing Corp. (APC) and the Jacksonville Electric Authority's (JEA)
J. D. Kennedy (KGS), Southside (SGS) and Northside Generating Stations (NGS).

Intracoastal Waterway (ICW)
This study area includes a 263 kilometer stretch of the ICW extending
from just north of Kings Bay, Georgia, south to Oak Hill, Florida (Fig. 2).
The mainland borders the ICW on the west; barrier islands to the east
separate the waterway from the Atlantic Ocean. Three inlets and the mouths
of three rivers link this stretch of the ICW to the Atlantic Ocean.
The study area was divided into eight arbitrary zones for the purpose of
data analysis. These zones are 20 to 40 kilometers in length, delineated by
bridges and other geographical landmarks recognizable during low level
flights.

This region includes many communities on both banks of the ICW. Major
communities are: Fernandina Beach, Jacksonville Beach, St. Augustine, Ormond
Beach, Daytona Beach and New Smyrna Beach. Tomoka and Anastasia State Parks,
Matanzas National Monument, and Cumberland Island National Seashore are
located within the study area.
The ICW is used by commercial vessels and tows unable to navigate long
stretches in the open ocean, and by pleasure craft. Small boat and
recreational facilities are found throughout the northeast section of the
waterway (NOAA 1982).
With the exception of the Fernandina and Daytona Beach areas (zones 1
and 7), the waterway is generally narrow, sheltered, protected from strong
winds and usually free of rough water. Depths of 3.6 m are reported
throughout the length of the waterway but significant shoaling and shifting
occurs, particularly around inlets and river mouths. Currents up to 7.4
km/hr may be encountered. Mean tidal ranges vary from 2 m at Fernandina
Beach (zone 1) to less than 1 m at Ponce de Leon Inlet (zone 8) (Southern
Waterway Guide 1983). Habitat varies from salt marsh'(zones 1 and 2) to
subtropical mangrove estuaries (zone 8). Waters are turbid and generally
void of aquatic vegetation with the exception of inlets and the southern
extremes of the study area (zones 7 and 8).

Three pulp mills and one generating station are located within the study
area: Container Corporation of America, Fernandina Beach, FL; ITT Rayonier
Mill, Fernandina Beach, FL; Gillman Paper Co., St. Marys, Georgia; and New
Smyrna Utilities, Ponce de Leon, FL. All of the these companies discharge
warm water into the ICW. The Ponce de Leon generating plant is presently
being phased out and was not operating during the course of this study.

METHODS
Aerial surveys were flown over both study areas between 8 July 1982 and
16 June 1983. Surveys were conducted twice monthly for each study area;
generally once during the week and once over the weekend. Only one survey









5


Figure 2. Intracoastal Waterway study area.


GEORGIA


Zone I



Zone 2

-Mi nem.
Zone 3



Zone 4


Z Zone 5


,-* Zone 6


Zone 7


ne 8


IA@"











was conducted over the ICW and one over the St. Johns River during the months
of November and December, respectively, because of inclement weather.

Flights were initiated and terminated at the Gainesville Regional
Airport. Surveys were conducted from a Cessna 1721 at altitudes of 150-170
meters and speeds between 128-150 km/hr. On 41 of 46 total surveys, the
right door was removed to provide an increased field of observation. The
same flight paths were followed over each study area during every census
(Figs. 3 and 4). The east and west banks of the St. Johns River were
surveyed separately. Only one pass was made over the ICW; generally both
banks were visible at once. The direction of the flight path (N-S vs. S-N)
over the ICW varied according to wind direction. Circles were made over all
inlets, over the discharge areas of power plants during the winter and over
all manatee sightings.
A principal observer sat in the right front seat and recorded the
number, activity and location of manatees in each designated zone. Manatees
within three body-lengths of each other were recorded as a group.
Photographs were taken of groups that were too large to count accurately.
Activity was recorded as feeding, resting, traveling or cavorting. Feeding
could be recognized by the presence of a manatee in a grassbed and a nearby
plume of suspended sediment in the water. Motionless manatees were recorded
as resting and swimming manatees as traveling. A group of manatees ( 3
animals) rolling, splashing or swimming in tight circles were considered to
be cavorting. The number of calves (animals one-half or less the size of an
average adult) was noted. A second observer sat in the back seat and
recorded boat traffic. Boats that were anchored or moving were tallied for
the period that the plane was over a particular zone. Docked and moored
boats were not counted. Direction of travel, boat type (recreational, sail,
commercial fishing, barge/tug, oceanliner or other) and size class (<7.3 m
and ? 7.3 m) were noted for each observation. The size classification was
chosen Based on findings by Beck et al. (1982) that these boat sizes
generally are powered by different engine types (outboard and stern-drive vs.
inboard for boats< 7.3 m and boats >7.3 m, respectively) and may have
differential impact on manatee injury and death.

Ambient air temperature, wind speed and direction, water turbidity,
cloud cover and glare were also recorded at the beginning of each survey.
Each flight was rated as excellent, good, fair or poor based on a subjective
evaluation of the latter four conditions. The percent bottom cover by
grassbeds for each zone was evaluated from sketches made every three months
during aerial surveys.
Patterns of relative manatee and boat abundance, boat type, manatee
group size and manatee behavior were evaluated using chi-square (Siegel 1956)
and analysis of variance (ANOVA) (Sokal and Rohlf 1969) procedures. Multiple
comparisons among means were made using Duncan's multiple range test for
means (Snedecor and Cochran 1980). An arcsine transformation was performed
on proportions (Snedecor and Cochran 1980). The Kendall's Tau rank
correlation coefficient and the Pearson product-moment correlation

1References to trade names do not imply Government endorsement of commercial
products.











Figure 3. Flight path over the St. Johns River.


River



Jacksonville


N


3km


Duval Co.
Cloy Co.


Green
TO Gr-N L
GAINESVILLE








8



Figure 4. Flight path over the Intracoastal Waterway.



GEORGIA


Lemim


GAINESVILLE











coefficient (Siegel 1956) were used to test for associations between pairs of
independent samples. The Mann-Whitney U Test (Siegel 1956) was used to
determine independence between means. Computations were performed-with
resources of the Northeast Regional Data Center, University of Florida,
Gainesville, Florida.

RESULTS
The Lower St. Johns River
Manatee Abundance

A total of 420 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 138.6, N = 12, P = .0001)
and quarters of the year (X2 = 116.0, N = 4, p = .0001) (Fig. 5). Peak
manatee counts were made in July 1982 and May 1983; the lowest numbers
occurred in February and March 1983. Counts were higher than expected during
the spring and summer months (April-September) and lower than expected during
the winter months (January-March).
The ratio of calves to total manatees sighted per survey varied from 0.0
to 0.18. The ratio of calves to adults for all surveys combined was 0.07.
Twenty out of twenty-nine (69%) total calf sightings were made during the
spring and summer months. No calves were sighted from December to mid May
(Table 1).
Manatees were most frequently sighted alone or in pairs (Fig. 6).
Groups of up to nine animals were seen cavorting along the river banks; the
largest aggregations (11 animals) were at industrial warm water outflows.
Group size did not vary significantly among months (F = 1.24, N = 12, p =
0.266) or quarters of the year (F = 0.65, N = 4, p 0.58).

Seasonal temperature change influenced total manatee counts (Fig. 7).
The number of manatees counted during each survey was positively correlated
with ambient air temperature (r 0.67, N = 22, p = 0.006).
There was no significant relationship between the survey conditions and
the number of manatees sighted (r = 0.29, N = 22, p = 0.18).' The number of
manatees counted was also independent of the day of the week (weekday vs.
weekend) on which the survey was conducted (Mann Whitney U14,se 43, p > 0.1).
The total number of manatees counted during each survey was independent of
the total number of boats counted (r = 0.25, N = 22, p = 0.25).

Manatee Distribution in the Study Area
Manatee counts (Fig. 8) and manatee densities (Table 2) varied within
the study area. Actual counts were highest from Green Cove Springs to
Buckman Bridge (zone 8), but the density of manatees (no. of manatees/linear
flight distance) was greatest in Doctor's Lake (zone 10). Few sightings were
made from Chaseville to the mouth of the river (zones 1-3); manatees were
sighted only around Blount Island (zone 2). No manatees were sighted in the
Ortega River (zone 7). There was a tendency for manatees sighted to the











coefficient (Siegel 1956) were used to test for associations between pairs of
independent samples. The Mann-Whitney U Test (Siegel 1956) was used to
determine independence between means. Computations were performed-with
resources of the Northeast Regional Data Center, University of Florida,
Gainesville, Florida.

RESULTS
The Lower St. Johns River
Manatee Abundance

A total of 420 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 138.6, N = 12, P = .0001)
and quarters of the year (X2 = 116.0, N = 4, p = .0001) (Fig. 5). Peak
manatee counts were made in July 1982 and May 1983; the lowest numbers
occurred in February and March 1983. Counts were higher than expected during
the spring and summer months (April-September) and lower than expected during
the winter months (January-March).
The ratio of calves to total manatees sighted per survey varied from 0.0
to 0.18. The ratio of calves to adults for all surveys combined was 0.07.
Twenty out of twenty-nine (69%) total calf sightings were made during the
spring and summer months. No calves were sighted from December to mid May
(Table 1).
Manatees were most frequently sighted alone or in pairs (Fig. 6).
Groups of up to nine animals were seen cavorting along the river banks; the
largest aggregations (11 animals) were at industrial warm water outflows.
Group size did not vary significantly among months (F = 1.24, N = 12, p =
0.266) or quarters of the year (F = 0.65, N = 4, p 0.58).

Seasonal temperature change influenced total manatee counts (Fig. 7).
The number of manatees counted during each survey was positively correlated
with ambient air temperature (r 0.67, N = 22, p = 0.006).
There was no significant relationship between the survey conditions and
the number of manatees sighted (r = 0.29, N = 22, p = 0.18).' The number of
manatees counted was also independent of the day of the week (weekday vs.
weekend) on which the survey was conducted (Mann Whitney U14,se 43, p > 0.1).
The total number of manatees counted during each survey was independent of
the total number of boats counted (r = 0.25, N = 22, p = 0.25).

Manatee Distribution in the Study Area
Manatee counts (Fig. 8) and manatee densities (Table 2) varied within
the study area. Actual counts were highest from Green Cove Springs to
Buckman Bridge (zone 8), but the density of manatees (no. of manatees/linear
flight distance) was greatest in Doctor's Lake (zone 10). Few sightings were
made from Chaseville to the mouth of the river (zones 1-3); manatees were
sighted only around Blount Island (zone 2). No manatees were sighted in the
Ortega River (zone 7). There was a tendency for manatees sighted to the











coefficient (Siegel 1956) were used to test for associations between pairs of
independent samples. The Mann-Whitney U Test (Siegel 1956) was used to
determine independence between means. Computations were performed-with
resources of the Northeast Regional Data Center, University of Florida,
Gainesville, Florida.

RESULTS
The Lower St. Johns River
Manatee Abundance

A total of 420 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 138.6, N = 12, P = .0001)
and quarters of the year (X2 = 116.0, N = 4, p = .0001) (Fig. 5). Peak
manatee counts were made in July 1982 and May 1983; the lowest numbers
occurred in February and March 1983. Counts were higher than expected during
the spring and summer months (April-September) and lower than expected during
the winter months (January-March).
The ratio of calves to total manatees sighted per survey varied from 0.0
to 0.18. The ratio of calves to adults for all surveys combined was 0.07.
Twenty out of twenty-nine (69%) total calf sightings were made during the
spring and summer months. No calves were sighted from December to mid May
(Table 1).
Manatees were most frequently sighted alone or in pairs (Fig. 6).
Groups of up to nine animals were seen cavorting along the river banks; the
largest aggregations (11 animals) were at industrial warm water outflows.
Group size did not vary significantly among months (F = 1.24, N = 12, p =
0.266) or quarters of the year (F = 0.65, N = 4, p 0.58).

Seasonal temperature change influenced total manatee counts (Fig. 7).
The number of manatees counted during each survey was positively correlated
with ambient air temperature (r 0.67, N = 22, p = 0.006).
There was no significant relationship between the survey conditions and
the number of manatees sighted (r = 0.29, N = 22, p = 0.18).' The number of
manatees counted was also independent of the day of the week (weekday vs.
weekend) on which the survey was conducted (Mann Whitney U14,se 43, p > 0.1).
The total number of manatees counted during each survey was independent of
the total number of boats counted (r = 0.25, N = 22, p = 0.25).

Manatee Distribution in the Study Area
Manatee counts (Fig. 8) and manatee densities (Table 2) varied within
the study area. Actual counts were highest from Green Cove Springs to
Buckman Bridge (zone 8), but the density of manatees (no. of manatees/linear
flight distance) was greatest in Doctor's Lake (zone 10). Few sightings were
made from Chaseville to the mouth of the river (zones 1-3); manatees were
sighted only around Blount Island (zone 2). No manatees were sighted in the
Ortega River (zone 7). There was a tendency for manatees sighted to the











coefficient (Siegel 1956) were used to test for associations between pairs of
independent samples. The Mann-Whitney U Test (Siegel 1956) was used to
determine independence between means. Computations were performed-with
resources of the Northeast Regional Data Center, University of Florida,
Gainesville, Florida.

RESULTS
The Lower St. Johns River
Manatee Abundance

A total of 420 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 138.6, N = 12, P = .0001)
and quarters of the year (X2 = 116.0, N = 4, p = .0001) (Fig. 5). Peak
manatee counts were made in July 1982 and May 1983; the lowest numbers
occurred in February and March 1983. Counts were higher than expected during
the spring and summer months (April-September) and lower than expected during
the winter months (January-March).
The ratio of calves to total manatees sighted per survey varied from 0.0
to 0.18. The ratio of calves to adults for all surveys combined was 0.07.
Twenty out of twenty-nine (69%) total calf sightings were made during the
spring and summer months. No calves were sighted from December to mid May
(Table 1).
Manatees were most frequently sighted alone or in pairs (Fig. 6).
Groups of up to nine animals were seen cavorting along the river banks; the
largest aggregations (11 animals) were at industrial warm water outflows.
Group size did not vary significantly among months (F = 1.24, N = 12, p =
0.266) or quarters of the year (F = 0.65, N = 4, p 0.58).

Seasonal temperature change influenced total manatee counts (Fig. 7).
The number of manatees counted during each survey was positively correlated
with ambient air temperature (r 0.67, N = 22, p = 0.006).
There was no significant relationship between the survey conditions and
the number of manatees sighted (r = 0.29, N = 22, p = 0.18).' The number of
manatees counted was also independent of the day of the week (weekday vs.
weekend) on which the survey was conducted (Mann Whitney U14,se 43, p > 0.1).
The total number of manatees counted during each survey was independent of
the total number of boats counted (r = 0.25, N = 22, p = 0.25).

Manatee Distribution in the Study Area
Manatee counts (Fig. 8) and manatee densities (Table 2) varied within
the study area. Actual counts were highest from Green Cove Springs to
Buckman Bridge (zone 8), but the density of manatees (no. of manatees/linear
flight distance) was greatest in Doctor's Lake (zone 10). Few sightings were
made from Chaseville to the mouth of the river (zones 1-3); manatees were
sighted only around Blount Island (zone 2). No manatees were sighted in the
Ortega River (zone 7). There was a tendency for manatees sighted to the






10

Figure 5. Number of manatees counted by month and quarter of the year in
the St. Johns River.


160

140
120
100
80
60
40
20


J A S O N D J F M AM
Month


JAS OND JFM
Quarters of year


AMJ











Table 1. Numbers and ratios of adults and calves sighted in the St. Johns
River.


St. Johns River

Survey No. of No. of Total No.
date adults calves c/a manatees
(a) (c)


8 Jul
21 Jul
4 Aug
28 Aug
14 Sep
25 Sep
5 Oct
16 Oct
2 Nov
31 Nov
18 Dec
4 Jan
25 Jan
9 Feb
25 Feb
9 Mar,
26 Mar
16 Apr
21 Apr
14 May
25 May
11 Jun
16 Jun


.136
.06
.08
0
.18
0
0
.2
.06
.18
0
0
0
0
.0
0
0
0
0
.11
.09
.05
.03


TOTALS 390 .07 420


TOTALS 390


.07 420












Figure 6. Frequency of group size in the St. Johns River.


I 2 3 4 5 6 7 8 9 10 II
Group size







13





Figure 7. Relationship between temperature and manatee counts in the
St. Johns River.










50 -50

-.- Temperature
Manatee
40- -40
0
IU
o
C
30 -30 3 "

%S S E
r -
20- 20


0 r \ /0 e


M J


Months













Figure 8. Number of manatees counted in ten zones in the St. Johns River.










200
180 /
160
140
I 120
1E 00
d 80so. 7-
g/ /
40
20. / /


5 6 '10 8


Zone












Table 2. Density of manatees in the zones of the St. Johns River. Density
values were calculated by dividing the linear distance (km) of the
flight path over each zone into the total number of manatees
sighted in each zone during quarters of the year.

Quarter of the Year Total
Zone JAS OND JFM AMJ Density

1 .07 .00 .00 .00 .07
2 .00 .00 .00 .38 .38
3 .00 .00 .03 .00 .03
4 .12 .00 .00 .24 .35
5 .00 .63 .45 .07 1.15
6 1.12 .95 .00 2.75 4.83
7 .00 .00 .00 .00 .00
8 3.35 2.08 .03 2.01 7.57
9 .00 .00 .00 .57 .57
10 4.85 2.57 .00 1.78 9.20

TOTALS 9.51 6.23 0.51 7.80 24.08










north (zone 6) and south (zone 8) of the Buckman Bridge to be on the east and
west banks of the river, respectively.

There were seasonal changes in manatee distribution within the study
area (Fig. 9, Table 2). Manatees were sighted in two zones in the east bend
of the river (zones 2 and 4) only during the spring and fall. All but two of
the sightings made between the Fuller Warren Bridge and Chaseville (zone 5)
occurred from November to March and were in the immediate vicinity of one of
three industrial, warm water outfalls located within the zone. The section
of the river south of the Fuller Warren Bridge (zones 6-10), was used by
manatees from spring to late fall (April-December); only one sighting
occurred from January to March.

Where manatees were frequently sighted, the counts were correlated with
changes in air temperature. The number of manatees increased significantly
with temperatures in the zones south of the Fuller Warren Bridge (r 0.47,
0.63, and 0.54 for zones 6, 8 and 10, respectively, N's = 23, p < 0.05).
Manatee counts were negatively correlated with air temperature in the
vicinity of the power plants (zone 5) (r = -0.54, N = 22, p = 0.009).

The percent bottom coverage by aquatic vegetation was the best predictor
of manatee abundance (Kendall's Tau = 0.76, N = 10, p = 0.004). Manatees
generally did not avoid zones with high boat traffic; the total density of
manatees per zone was not significantly correlated with the density of boats
per zone (Kendall's Tau = 11.0, N 10, p >0.1). However, within such zones
manatees were generally sighted along the banks of the river, away from the
center of traffic. When the relationship between manatee and boat densities
was examined for each zone separately, only one zone (zone 5) showed a
significant negative correlation (Kendall's Tau = -0.36, N a 22, p = 0.03)
between the density of manatees and boats calculated for each survey.

Manatee Movements and Behavioral Patterns

Doctors Lake (zone 10) and the stretch of the river from Green Cove
Springs to the Buckman Bridge (zone 8) were the major feeding and resting
grounds (Fig. 10). A few animals were observed feeding on shoreline
vegetation further down the river where no grassbeds were present. Warm
water outfalls were the principal resting grounds during the winter months.
Groups of cavorting manatees were sighted in tributaries, coves, marinas and
isolated shorelines. Cavorting manatees were most frequently observed on the
east bank of the river approximately eight kilometers south of the Ortega
River near a residential section with little human activity. Traveling
manatees were observed throughout the study area and were generally sighted
along the banks of the river, away from boat channels.
Cavorting and traveling manatees comprised the greatest percentage of
observations from April to June. Sightings of feeding manatees comprised the
greatest percentage of observations from July to September. An overwhelming
proportion of manatee activities observed from October to March was of
resting animals (Table 3).












Seasonal distribution of manatees in the St. Johns River.
Size of dot indicates the number of manatees per location:
o= 1; *= 2-5; *= 6-10; = >11.


Oct- Dec


.46ftWmM


3km




---3
SR. .;;;.i C. .


Ore Cu i


Jan- Mar


Figure 9.


Jul-Sep


Gren Con so"s


Apr-Jun










Figure 10.


Activity of manatees in the St. Johns River.
number of manatees per location: o0 1; *=
0= > 11.


Size of dot indicates
2-5; 0= 6-10;


4'


VOW Ca


om can


Feeding


Resting


JasasWils


4'e


I 1..C


caL c


Cavorting


JsaMOiale


ctmaC


Traveling











Table 3. Frequency and
Johns River.


percent per season of manatee activity in the St.


RESTING

N (%)
38 (13)
66 (58)

11 (79)
31 (23)


BEHAVIORS
CAVORTING

N (%)
38 (10)

1 (0)

0 (0)
46 (35)


TRAVELING

N (%)
16 (10)
28 (25)
2 (14)
36 (27)


TOTALS
N (%)
1591(100)
1142(100)

14 (100)
1333(100)

420


1Three individuals were tallied for two different behaviors.
2Behaviors were not determined for two individuals.
3Behavior was not determined for one individual.


SEASON


JUL-SEPT
OCT-DEC

JAN-MAR
APR-JUN

TOTALS


FEEDING

N (%)
67 (42)
19 (17)

1 (7)
20 (15)










Boat Traffic

A one-way analysis of variance showed that boat traffic varied
significantly in abundance between months (F = 34, N = 12, p = 0.26) and
quarters of the year (F = 4.22, N = 4, p = 0.01) (Fig. 11). Mean monthly
boat counts for August and September were significantly higher than all other
months and the mean boat count for the summer quarter (July-September) was
significantly higher than all other quarters (p a 0.05). The mean number of
boats counted over weekends was significantly higher than the mean number of
boats counted during weekdays (t = -2.34, N = 23, p = 0.04). This
relationship was accredited to a significant increase in small recreational
boats over the weekends (F = 7.24, N = 23, p = 0.01).

Eighty-five percent of all boat traffic was classified as recreational
and eighty percent of the traffic was less than 7.3 m in length. The
remainder of the traffic was comprised primarily of commercial fishing
vessels, barges and motor-sailboats.
The frequency of seven boat types varied significantly among and within
seasons (X2 = 80.8, N = 2713, p = 0.0001) (Table 4). The greatest deviations
from the expected frequencies came from the high number of small recreational
boats counted during the summer and the low number counted during the fall
and winter. In contrast to small boats, larger recreational boats were fewer
in number than would be expected during the summer. Other large deviations
from expected frequencies were due to a high amount of barge traffic from
January to March and a low amount from July to September.
The distribution of boat traffic varied within the study area (Table 5).
Boat density was highest at the mouth of the river (zone 1) and in Doctors
Lake (Zone 10). The lowest boat densities were calculated for the
Chaseville-Mill Cove area (Zone 3) and the Ortega River (zone 7). Boat type
varied significantly within zones (ANOVA, p < 0.05); the mean number of small
recreational boats was significantly higher than the means of all other boat
types in every zone (Duncan's multiple range test, p = 0.05). Figure 12
summarizes the distribution of boat types (excluding sailboats) within the
study area based on the relative density values of each-boat type in all
zones. Recreational boats are found throughout the study area with major
concentrations occurring near the mouth of the river (zone 1), Doctors Lake
(zone 10) and the Ortega River (zone 7). The density of commercial fishing
boats is greatest around Blount Island (zone 2) and barges, oceanliners and
other large industrial vessels are densest in the narrow region of the river
from the Fuller Warren Bridge to Chaseville (Zone 5).

Boat activity varied significantly among and within seasons (X2 = 78.7,
N = 2643, p = 0.0001). The greatest deviations from the expected frequencies
came from the large number of boats traveling north from July to September
and a larger than expected number traveling south from January to March.
Other large deviations were due to greater than expected numbers of anchored
boats in the spring (April-June) and fall (Oct-Dec) and lower than expected
numbers of anchored boats in the winter (January-March). The activity of
boats varied significantly among and within all zones (X2 = 406.2, N = 2643,
p = 0.0001). The greatest deviations from the expected frequencies came from
the large number of boats moving perpendicular to the channel in the
industrial zone (zone 5) and the large number of anchored boats in zone 1.










Figure 11. Number of boats counted by month and quarter of the year in
the St. Johns River.


450

390

330

290

210

150

90.

30


1500

1300

1100

I 900

S700

z 500

300

100


J A S O N J F M A M
Month


JAS OND JFM
Quarter of year


AMJ








22








Table 4. Seasonal abundance of six boat classes in the St. Johns River.

BOAT CLASS
RECREATIONAL RECREATIONAL COMMERCIAL MOTOR BARGE OCEAN LINER &
SEASON (< 7.3 m) (2.7.3 m) FISHING SAIL TUC UNCLASSIFIED TOTALS
Jul-Sep 914 46 47 56 24 15 1102
Oct-Dec 388 40 25 24 25 3 505
Jen-Mar 232 20 11 13 27 11 314
Apr-Jun 637 56 6 38 42 13 792

TOTALS 2171 162 89 131 118 42 2713







23




Table 5. Density of six boat classes in ten zones of the St. Johns River. Boat densities were
calculated by dividing the linear flight distance (km) per zone into the total number
of boats of each class counted in each zone.


RECREATIONAL
(<7.3 m)
22.7

15.6

9.1

4.2

5.6

10.5

5.5

13.7

15.1

21.4


RECREATIONAL
(2.7.3 m)
1.51

0.54
0.63

0.47

0.59

1.06

1.27

0.97

0.85

1.38


BOAT CLASS

COMMERCIAL
FISHING

0.38

1.5

0.35

0.23

0.85

1.0

0

0.07

0

0.19


MOTOR
SAIL

0.48

0.78

0.48

0.27

0.76

2.21

0.43

1.08

0.55

0.93


BARGE OCEANLINERS
& OTHER INDUSTRIAL

1.23

1.08

0.84

0.23

2.2

0.33

0

0.48

0

0


ZONE
1

2

3

4

5

6

7

8

9

10


TOTALS

26.3

19.5

11.4

5.4

10

15.1

7.2

16.3

16.9

23.9







24


Figure 12.


Distribution of four boat classes in the St.
intensity indicates the density of each boat
*= high; = med; = low.


Johns
class


River. Shading
per zone:


^ ~..
.C1


'00
0" Li


S. Ja C
I I -




..,iao'C
*'.' ^ ""'t _


C -lid


mr-- C- 1S@97WS

Recreational
('7.3m long)


Recreational
(>7.3m long)


JlujmU


J& I




L I ir-..
,L J .mu C.


Commercial fishing
Commercial fishing


Barges, oceanliners

other industrial
other industrial


Jesuenme


UtJuinp Ci.


icw










Intracoastal Waterway

Manatee Abundance

A total of 134 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 = 107.3, N = 6, p = 0.0001)
and quarters of the year (X2 = 72.2, N = 4, p = 0.0001) (Fig. 13). Manatee
counts were highest during the spring and summer with peak counts in
September 1982 and May 1983. The period of lowest utilization was during the
late fall and winter months (October-March); only three manatees were
observed from November to February.

The ratio of calves to total manatees observed per survey varied from
0.0 to 0.14. The ratio of calves to adults for all surveys combined was
0.04. All but one of the calf sightings were made within the spring months
(April-June) (Table 6).

Manatees were most frequently sighted as singles (N = 43); however, the
majority of the sightings were of manatees accompanying other manatees (N =
91) (Fig. 14). Larger groups (up to 11 animals) were observed at inlets to
the Atlantic Ocean. As many as five animals were observed in groups in or
around industrial warm water outfalls during the early spring months. One
group of twenty manatees was sighted aggregated close to shore in zone eight,
apparently drinking fresh water runoff.

Seasonal temperature change did not influence total counts (Fig. 15);
the number of manatees counted during each survey was not significantly
correlated with changes in ambient air temperature (r = 0.3, N = 23, p =
.15).
There was no significant relationship between survey conditions and the
number of manatees sighted (r = 0.24, N = 24, p = 0.24). On days when
manatees were sighted, the number of manatees counted was independent of the
day of the week (weekday vs. weekend) on which the survey was conducted (Mann
Whitney U12,5= 18, p > 0.1). The total number of manatees counted per survey
was also independent of the total number of boats counted (r = 0.15, N = 22,
p = 0.49).

Manatee Distribution in the Study Area

Manatees were sighted throughout the entire study area but the number of
sightings and the density of manatees varied among zones (Fig. 16 and Table
7). Manatee counts and densities were highest in the most southern and
northern zones (zones 1 and 8, respectively), followed in number by the
stretch of the ICW from Flagler Beach to Port Orange (zone 7). The majority
of the sightings in the latter zone were made in the vicinity of the Tomoka
River. The two most heavily used zones both had one or more inlets to the
Atlantic Ocean.

There were seasonal changes in manatee distribution within the study
area (Fig. 17, Table 7). Manatees were sighted throughout the ICW during the
spring months (April-June). Manatee sightings in the northern zones (zones
1-5) were more frequent during the spring. Summer and fall sightings










Intracoastal Waterway

Manatee Abundance

A total of 134 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 = 107.3, N = 6, p = 0.0001)
and quarters of the year (X2 = 72.2, N = 4, p = 0.0001) (Fig. 13). Manatee
counts were highest during the spring and summer with peak counts in
September 1982 and May 1983. The period of lowest utilization was during the
late fall and winter months (October-March); only three manatees were
observed from November to February.

The ratio of calves to total manatees observed per survey varied from
0.0 to 0.14. The ratio of calves to adults for all surveys combined was
0.04. All but one of the calf sightings were made within the spring months
(April-June) (Table 6).

Manatees were most frequently sighted as singles (N = 43); however, the
majority of the sightings were of manatees accompanying other manatees (N =
91) (Fig. 14). Larger groups (up to 11 animals) were observed at inlets to
the Atlantic Ocean. As many as five animals were observed in groups in or
around industrial warm water outfalls during the early spring months. One
group of twenty manatees was sighted aggregated close to shore in zone eight,
apparently drinking fresh water runoff.

Seasonal temperature change did not influence total counts (Fig. 15);
the number of manatees counted during each survey was not significantly
correlated with changes in ambient air temperature (r = 0.3, N = 23, p =
.15).
There was no significant relationship between survey conditions and the
number of manatees sighted (r = 0.24, N = 24, p = 0.24). On days when
manatees were sighted, the number of manatees counted was independent of the
day of the week (weekday vs. weekend) on which the survey was conducted (Mann
Whitney U12,5= 18, p > 0.1). The total number of manatees counted per survey
was also independent of the total number of boats counted (r = 0.15, N = 22,
p = 0.49).

Manatee Distribution in the Study Area

Manatees were sighted throughout the entire study area but the number of
sightings and the density of manatees varied among zones (Fig. 16 and Table
7). Manatee counts and densities were highest in the most southern and
northern zones (zones 1 and 8, respectively), followed in number by the
stretch of the ICW from Flagler Beach to Port Orange (zone 7). The majority
of the sightings in the latter zone were made in the vicinity of the Tomoka
River. The two most heavily used zones both had one or more inlets to the
Atlantic Ocean.

There were seasonal changes in manatee distribution within the study
area (Fig. 17, Table 7). Manatees were sighted throughout the ICW during the
spring months (April-June). Manatee sightings in the northern zones (zones
1-5) were more frequent during the spring. Summer and fall sightings










Intracoastal Waterway

Manatee Abundance

A total of 134 manatees were observed during 23 surveys. Manatee
abundance varied significantly among months (X2 = 107.3, N = 6, p = 0.0001)
and quarters of the year (X2 = 72.2, N = 4, p = 0.0001) (Fig. 13). Manatee
counts were highest during the spring and summer with peak counts in
September 1982 and May 1983. The period of lowest utilization was during the
late fall and winter months (October-March); only three manatees were
observed from November to February.

The ratio of calves to total manatees observed per survey varied from
0.0 to 0.14. The ratio of calves to adults for all surveys combined was
0.04. All but one of the calf sightings were made within the spring months
(April-June) (Table 6).

Manatees were most frequently sighted as singles (N = 43); however, the
majority of the sightings were of manatees accompanying other manatees (N =
91) (Fig. 14). Larger groups (up to 11 animals) were observed at inlets to
the Atlantic Ocean. As many as five animals were observed in groups in or
around industrial warm water outfalls during the early spring months. One
group of twenty manatees was sighted aggregated close to shore in zone eight,
apparently drinking fresh water runoff.

Seasonal temperature change did not influence total counts (Fig. 15);
the number of manatees counted during each survey was not significantly
correlated with changes in ambient air temperature (r = 0.3, N = 23, p =
.15).
There was no significant relationship between survey conditions and the
number of manatees sighted (r = 0.24, N = 24, p = 0.24). On days when
manatees were sighted, the number of manatees counted was independent of the
day of the week (weekday vs. weekend) on which the survey was conducted (Mann
Whitney U12,5= 18, p > 0.1). The total number of manatees counted per survey
was also independent of the total number of boats counted (r = 0.15, N = 22,
p = 0.49).

Manatee Distribution in the Study Area

Manatees were sighted throughout the entire study area but the number of
sightings and the density of manatees varied among zones (Fig. 16 and Table
7). Manatee counts and densities were highest in the most southern and
northern zones (zones 1 and 8, respectively), followed in number by the
stretch of the ICW from Flagler Beach to Port Orange (zone 7). The majority
of the sightings in the latter zone were made in the vicinity of the Tomoka
River. The two most heavily used zones both had one or more inlets to the
Atlantic Ocean.

There were seasonal changes in manatee distribution within the study
area (Fig. 17, Table 7). Manatees were sighted throughout the ICW during the
spring months (April-June). Manatee sightings in the northern zones (zones
1-5) were more frequent during the spring. Summer and fall sightings











Figure 13. Number of manatees counted
the Intracoastal Waterway.


by month and quarters of the year in


39


33-


27-

21


J AS 0 nD
Month


-__ I _


F M A M J


JAS OND JFM

Quarters of year


AMJ











Table 6. Numbers and ratio of calves to adults sighted in the Intracoastal
Waterway.

Survey No. of No. of Total No.
Date Adults calves c/a Manatees
(a) (c)
9 Jul 11 1 .09 12
23 Jul 2 0 0 2
9 Aug 1 0 0 1
28 Aug 2 0 0 2
16 Sep 38 0 0 38
28 Sep 1 0 0 1
7 Oct 9 0 0 9
17 Oct 1 0 0 1
6 Nov 0 0 0 0
2 Dec 2 0 0 2
19 Dec 0 0 0 0
6 Jan 0 0 0 0
29 Jan 0 0 0 0
12 Feb 0 0 0 0
29 Feb 0 0 0 0
14 Mar 1 0 0 1
29 Mar 5 0 0 5
.5 Apr 7 1 .14 8
17 Apr 3 0 0 3
10 May 15 2 .13 17
15 May 9 1 .11 10
I Jun 17 0 17
11 Jun 5 0 0 5

TOTALS 129 5 .04 134








28




Figure 14. Frequency of group size in the Intracoastal Waterway.


42-
39

36

33-
30

27
3 24.

21.
o
S 18.
z
15'
12.
9-

3-
63
3'


i~mnm


I 2 3 4 5 6 7 8 9 10


m rn


Group size


, -- -


I '


HX


20












Figure 15.




















U
o

"5
c
a


z


Relationship between temperature and manatee counts in the
Intracoastal Waterway.
















40 Manatees 40
I Temperature


20
30- -30




%e 0 AIt .
20- / |


2 / \ o \
10 \ l -0
A A


Months







30




Figure 16. Number of manatees counted in eight zones of the Intracoastal
Waterway.







55

50

45

40

S35

S30

z25

S20
15,

10



4 3 2 6 5 7 1 8
Zone










Table 7. Density of manatees in eight zones of the Intracoastal Waterway.
Density values were calculated by dividing the linear distance (km)
of the flight path over each zone, into the total number of
manatees sighted in each zone during quarters of the year.
TOTAL
ZONE JUL-SEP OCT-DEC JAN-MAR APR-JUN DENSITY

1 .26 .00 .12 .26 .64

2 .00 .00 .00 .29 .29

3 .00 .00 .00 .11 .11

4 .00 .00 .00 .06 .06

5 .00 .00 .00 .46 .46

6 .11 .00 .00 .11 .22

7 .15 .05 .00 .41 .61

8 .84 .24 .02 .22 1.32

TOTALS 1.36 .29 .14 1.92 3.71



































Figure 17. Seasonal distribution of manatees in the Intracoastal Waterway.
Size of dot indicates the number of manatees per location:
o = 1; 2-5; *= 6-10; = 11.


































S L



1C
* -^ ,v ; u
^ ^-^c
\^ '* ., ^


garea


"am&n


gOMIA


Jul- Sep


Oct-Dec


9


Jan-


Apr-Jun


' -- .


Ik


c

L











increased progressively to the south. Late fall and early spring sightings
were most frequent in the vicinity of the Fernandina Beach industrial warm
water outfalls (zone 1).

The number of manatees sighted in each zone varied with seasonal changes
in air temperature. The number of sightings in each zone increased with air
temperature; however, the relationships were not significant (p > 0.1).
Manatees did not avoid areas with high boat traffic; the density of
manatees per survey zone was not significantly correlated with the density of
boats (Kendall's Tau = -3.0, N = 8, p >0.1). When the relationship between
manatee and boat densities was examined for each zone separately, one zone
(zone 8) showed a significant positive correlation between the number of
manatees and boats (Kendall's Tau = 0.36, N =23, p = 0.03).

Manatee Movements and Behavioral Patterns

Manatees used the ICW for traveling more frequently than for any other
behavior (Table 8). Observations of resting and cavorting manatees were
infrequent and feeding manatees were noted only five times. The greatest
percentages of animals observed traveling were during the spring and late
summer. Manatees were observed traveling throughout the entire study area
(Fig. 18). However, the majority of the sightings, with the exception of
those animals observed in and around the Tomoka River (zone 6), were in the
vicinity of inlets connecting with the Atlantic Ocean. Eighty-two percent (N
= 110) of all traveling manatees were sighted within five meters of the
shoreline, the remaining 18 percent (N 24) were observed in the middle of
boat channels. Of the few manatees observed resting or cavorting, all were
sighted in cut-offs, small tributaries or in shallow areas near the waterway
banks. In all but one observation of feeding manatees, the animals were
feeding on shoreline vegetation with the upper half of their body hauled out
of the water.

Boat Traffic

A one-way analysis of variance showed that boat traffic did not vary
significantly in abundance between months (F 0.77, N = 12, p = 0.66) and
quarters (F 1.9, N = 4, p = 0.16) of the year (Fig. 19). However, boat
counts peaked in April and May and there was a trend towards higher boat
counts during the summer quarter. The mean number of boats counted on
weekends was significantly higher than the mean number of boats counted
during the week (Student's t-test = 2.7, N = 23, p = 0.01).

Eighty-one percent of all boat traffic was classified as recreational
and 66 percent of the traffic was less than 7.3 m in length. The remainder
of the traffic was comprised primarily of large motorsail vessels ( 7.3 m)
and, to a lesser degree, barges and commercial fishing vessels (Table 9).
The frequency of seven boat types varied significantly among and within
seasons (X2 = 215.7, N a 4563, p = 0.0001). The greatest deviations from the
expected frequencies were due to a the large number of small recreational
boats in the summer and the low number in the spring. In contrast to small











increased progressively to the south. Late fall and early spring sightings
were most frequent in the vicinity of the Fernandina Beach industrial warm
water outfalls (zone 1).

The number of manatees sighted in each zone varied with seasonal changes
in air temperature. The number of sightings in each zone increased with air
temperature; however, the relationships were not significant (p > 0.1).
Manatees did not avoid areas with high boat traffic; the density of
manatees per survey zone was not significantly correlated with the density of
boats (Kendall's Tau = -3.0, N = 8, p >0.1). When the relationship between
manatee and boat densities was examined for each zone separately, one zone
(zone 8) showed a significant positive correlation between the number of
manatees and boats (Kendall's Tau = 0.36, N =23, p = 0.03).

Manatee Movements and Behavioral Patterns

Manatees used the ICW for traveling more frequently than for any other
behavior (Table 8). Observations of resting and cavorting manatees were
infrequent and feeding manatees were noted only five times. The greatest
percentages of animals observed traveling were during the spring and late
summer. Manatees were observed traveling throughout the entire study area
(Fig. 18). However, the majority of the sightings, with the exception of
those animals observed in and around the Tomoka River (zone 6), were in the
vicinity of inlets connecting with the Atlantic Ocean. Eighty-two percent (N
= 110) of all traveling manatees were sighted within five meters of the
shoreline, the remaining 18 percent (N 24) were observed in the middle of
boat channels. Of the few manatees observed resting or cavorting, all were
sighted in cut-offs, small tributaries or in shallow areas near the waterway
banks. In all but one observation of feeding manatees, the animals were
feeding on shoreline vegetation with the upper half of their body hauled out
of the water.

Boat Traffic

A one-way analysis of variance showed that boat traffic did not vary
significantly in abundance between months (F 0.77, N = 12, p = 0.66) and
quarters (F 1.9, N = 4, p = 0.16) of the year (Fig. 19). However, boat
counts peaked in April and May and there was a trend towards higher boat
counts during the summer quarter. The mean number of boats counted on
weekends was significantly higher than the mean number of boats counted
during the week (Student's t-test = 2.7, N = 23, p = 0.01).

Eighty-one percent of all boat traffic was classified as recreational
and 66 percent of the traffic was less than 7.3 m in length. The remainder
of the traffic was comprised primarily of large motorsail vessels ( 7.3 m)
and, to a lesser degree, barges and commercial fishing vessels (Table 9).
The frequency of seven boat types varied significantly among and within
seasons (X2 = 215.7, N a 4563, p = 0.0001). The greatest deviations from the
expected frequencies were due to a the large number of small recreational
boats in the summer and the low number in the spring. In contrast to small










Table 8. Frequency and percent per
Intracoastal Waterway.


season of manatee activity in the


BEHAVIOR


SEASON


JUL-SEP
OCT-DEC
JAN-MAR
APR-JUN

TOTALS


FEEDING

N (%)
1 (0)
1 (8)
0 (0)

3 (5)


RESTING

N (%)
25 (45)

0 (0)
4 (67)
11 (18)


CAVORTING

N (%)
10 (18)

0 (0)
0 (0)
14 (23)


TRAVELING

N (%)
21 (37)
11 (92)

2 (33)
33 (54)


TOTALS

N (%)
571(100)

12(100)
6(100)
611(100)

136


O1ne individual was tallied for two different behaviors.


BEHAVIOR

































Figure 18.


Activity of manatees in the Intracoastal Waterway.
dot indicates the number of manatees per location:
* 2-5; 0 = 6-10; *= >11.


Size of
o = 1;
























Resting


SR


Cavorting


Feeding


mEoiA


Traveling


0 ;>


:c-~
-. L


I!


m J .JI


'C~-~2-,









Figure 19. Number of boats counted by month and quarter of the year in
the Intracoastal Waterway.


650
550
450
350
250
150
50



1500-
1300'
1100.
900
700-
500
300.
100.


Month




1 -


i//

////
/ V /-^


JAS OND JFM
Quarter of year


AMJ
















Table 9. Seasonal abundance of six boat classes in the Intracoastal Waterway.

BOAT CLASS
SEASON RECREAT I ONAL RECREATIONAL COMMERCE I AL MOTOR BARGE OCEANL I NER
.(<7.3 m) (27.3 a) FISHING SAIL TUG & UNCLASSIFIED TOTALS
JUL-SEP 780 117 26 93 17 3 1036
OCT-DEC 652 153 20 226 8 5 1064
JAN-MAR 624 98 22 105 16 12 877
APR-JUN 954 336 21 184 67 24 1586

TOTALS 3010 704 89 608 108 44 4563











boats, large recreational boats were observed in greater numbers than
expected during the spring. Other large deviations from expected frequencies
resulted from a large number of motor-sail boats during the winter months.

The distribution of boat traffic varied within the study area (Table
10). Boat densities were highest in the vicinity of Ponce de Leon Inlet
(zone 8), St. Augustine Inlet (zone 5), and the intersection of the ICW
and the St. Johns River (zone 2). The lowest boat density was between
Flagler Beach and Port Orange (zone 7), the only zone without a nearby inlet.
Boat type varied significantly within each zone (ANOVA, p < 0.05); the mean
number of small recreational boats was significantly higher than the means of
all other boat types in each zone (p = 0.05). When small recreational boats
are excluded from the analysis, the mean numbers of large recreational boats
and motor-sailboats are significantly higher in all but the two most northern
zones. Figure 20 summarizes the distribution of four boat classes
(excluding sailboats) within the study area based on the relative density
values of each boat type in each zone. Major concentrations of recreational
traffic are found in the three zones (2, 5 and 8) responsible for the highest
density of boat traffic. The density of both fishing and industrial vessels
are the greatest in the two most northern zones of the study area (zones 1
and 2).

Boat activity varies significantly among and within seasons (X2 = 132.9,
N = 4037, p = 0.0001). The greatest deviations from the expected frequencies
were due to a high number of boats moving north in the spring and a low
number moving north in the fall. In contrast, a much greater than expected
number of boats were moving south during the fall and a lower number than
expected were moving south during the spring. The activity of boats varied
significantly among and within zones (X2 = 168.6, N = 4037, p = 0.0001). The
greatest deviations from the expected frequencies came from large numbers of
boats anchored in those zones with inlets and large numbers of traveling
boats in those zones without inlets.

DISCUSSION
The Lower St. Johns River

Results of the present study support Hartman's (1974) observation that
manatee abundance and distribution in the lower St. Johns River are
correlated with water temperatures and food resources. Manatees were most
abundant in the study area during the summer months when air and water
temperatures are highest. Manatee intolerance to cold (Irvine 1983) limits
their use of the river during winter months when ambient river water
temperatures average below 19 to 160C, the range often cited as the threshold
of tolerance (Allsopp 1969, Campbell and Irvine 1981). Increased winter
manatee counts were recorded only for zone five, where aggregations of
manatees (up to 13 animals) were sighted in the warm water outfalls of two
generating stations and one industrial plant. These aggregations also are
limited by the low winter river water temperature; the aggregations are
unstable and composed primarily of transient individuals (Kinnaird and Valade
1983).











boats, large recreational boats were observed in greater numbers than
expected during the spring. Other large deviations from expected frequencies
resulted from a large number of motor-sail boats during the winter months.

The distribution of boat traffic varied within the study area (Table
10). Boat densities were highest in the vicinity of Ponce de Leon Inlet
(zone 8), St. Augustine Inlet (zone 5), and the intersection of the ICW
and the St. Johns River (zone 2). The lowest boat density was between
Flagler Beach and Port Orange (zone 7), the only zone without a nearby inlet.
Boat type varied significantly within each zone (ANOVA, p < 0.05); the mean
number of small recreational boats was significantly higher than the means of
all other boat types in each zone (p = 0.05). When small recreational boats
are excluded from the analysis, the mean numbers of large recreational boats
and motor-sailboats are significantly higher in all but the two most northern
zones. Figure 20 summarizes the distribution of four boat classes
(excluding sailboats) within the study area based on the relative density
values of each boat type in each zone. Major concentrations of recreational
traffic are found in the three zones (2, 5 and 8) responsible for the highest
density of boat traffic. The density of both fishing and industrial vessels
are the greatest in the two most northern zones of the study area (zones 1
and 2).

Boat activity varies significantly among and within seasons (X2 = 132.9,
N = 4037, p = 0.0001). The greatest deviations from the expected frequencies
were due to a high number of boats moving north in the spring and a low
number moving north in the fall. In contrast, a much greater than expected
number of boats were moving south during the fall and a lower number than
expected were moving south during the spring. The activity of boats varied
significantly among and within zones (X2 = 168.6, N = 4037, p = 0.0001). The
greatest deviations from the expected frequencies came from large numbers of
boats anchored in those zones with inlets and large numbers of traveling
boats in those zones without inlets.

DISCUSSION
The Lower St. Johns River

Results of the present study support Hartman's (1974) observation that
manatee abundance and distribution in the lower St. Johns River are
correlated with water temperatures and food resources. Manatees were most
abundant in the study area during the summer months when air and water
temperatures are highest. Manatee intolerance to cold (Irvine 1983) limits
their use of the river during winter months when ambient river water
temperatures average below 19 to 160C, the range often cited as the threshold
of tolerance (Allsopp 1969, Campbell and Irvine 1981). Increased winter
manatee counts were recorded only for zone five, where aggregations of
manatees (up to 13 animals) were sighted in the warm water outfalls of two
generating stations and one industrial plant. These aggregations also are
limited by the low winter river water temperature; the aggregations are
unstable and composed primarily of transient individuals (Kinnaird and Valade
1983).













Table 10. Density of six boat classes for eight zones in the Intracoastal Waterway. Boat
densities were calculated by dividing the linear flight distance (km) per zone into
the total number of boats of each class counted in each zone.


RECREAT IONAL
( <7.3 m)

6.4

16.8

11.4

11.2

16.5

10.1

8.8

17.2


RECREATIONAL
(27.3 m)

1.7

2.7

2.9

1.7

2.8

2.6

2.4

4.7


BOAT CLASS

COMMERCE I AL
FISHING

0.81

0.75

0.55

0.09

0.51

0.16

0.19

0.23


MOTOR
SAIL

1.87

2.13

2.0

2.22

3.14

1.97

2.04

3.46


BARGE OCEANLINER
OTHER INDUSTRIAL

1.02

1.22

0.25

0.09

0.35

0.37

1.07

0.31


ZONE

1

2

3

4

5

6

7

8


TOTALS

11.8

23.6

17.1

15.3

23.3

15.2

14.5

25.9


"I


*
































Figure 20.


Distribution of four boat classes in the Intracoastal Waterway.
Shading intensity indicates the density of each boat class per
zone: 3= high; m= med; Z= low.



















Recreational
('7.3m long)


Recreational
(>7.3m long)


t \


rac4la


fishing


a
other industrial


.. GEAcOM


Ac
~










The increase in the number of manatees during the summer months
represents an influx of animals from elsewhere into the study area. It is
not known where these animals spend the winter. However, a few winter
residents from Blue Spring, a natural warm water refuge approximately 170 km
to the south, have migrated as far as the city of Green Cove Springs during
the summer (Bengtson 1981). Perhaps some Blue Spring residents were involved
in this influx. However, there are only about 35 Blue Spring residents (as
of 1982/1983) and most of those winter south of this area (Bengtson 1981,
Sirenia Project, unpubl. data). It has been speculated that animals ranging
up and down the east coast of Florida may frequent the lower St. Johns during
their annual north/south migration (Kinnaird and Valade 1983). This idea is
supported by the greater number of manatees sighted traveling up and down the
river during the spring and fall, respectively. I believe most of the
manatees which summer in the lower St. Johns River winter at the Jacksonville
power plants or the lower east coast of Florida.
Manatee distribution during the summer months was correlated with the
location of submergent aquatic vegetation. Doctors Lake (zone 10) and the
section of river from the Buckman Bridge south to the city of Green Cove
Springs (zone 8) are bordered by beds of eelgrass (Vallisneria americana) and
constitute important feeding and resting grounds for manatees. Manatees
showed a preference for the west bank of zone eight and the southwest edge of
Doctors Lake where grassbeds are more lush and fewer shoals are present than
other sites. Food resources are extremely limited to the north of these two
zones; no grassbeds were visible from the air although mats of floating
vegetation were occasionally observed. Manatees in the lower St. Johns River
are known to consume cordgrass (Spartina bakeri) (Sirenia Project, FWS
unpubl. data). The few manatees observed feeding outside of zones with
grassbeds were consuming overhanging shoreline vegetation which was presumed
to be cordgrass.
Summer distribution within the study area also may be influenced by
salinity. Hartman (1974, 1979) observed a preference by manatees for the
mouths of rivers and other fresh water runoffs. During this study manatees
were rarely sighted north of the zone of transition between fresh and salt
water and those sighted beyond the zone were generally-near the mouths of
fresh water tributaries (i.e. Arlington and Trout Rivers) or during the
winter in the warm water outfalls.
The fact that very few sightings were made from the mouth of the river
to Mill Cove (zones 1-3) may be due to the extremely high water turbidity of
the area or because manatees are generally traveling through the area, not
stopping to rest or feed, thus making sightings less likely. Because
manatees are traveling to and from the power plants during the cooler months
and animals from outside the study area are moving into the Green Cove
Springs zone during the warmer months, manatees likely are present year-round
in that stretch of the river.
The proportion of calves sighted (7%) is somewhat lower than that
reported by other researchers. Campbell and Irvine (1978) observed 9.6% and
14.4% calves during winter and summer aerial surveys respectively over the
entire state of Florida. Calves made up 5.2% of the animals sighted by Odell
(1979) in Collier and Monroe Counties but Campbell and Irvine (1978) reported
10.2% of their sightings were calves from surveys over the same area.










Leatherwood (1979) and Shane (1983) reported 9.9% and 8.9% calves,
respectively from aerial surveys over the Indian and Banana Rivers. Rose and
McCutcheon (1980) reported 9% calves on winter surveys over power plants on
both coasts of Florida. Packard (1981) estimated that 14% of all manatees
sighted during the winter in the Hobe Sound area were calves. Irvine et al.
(1981) reported the only figure for the percentage of calf sightings that is
lower than the figure reported here; the total percentage of calves estimated
by the authors ranged from 0.9% to 4.9% in different months.

The relatively low proportion of calves reported for this study may be
affected, in part, by the absence of calves from the study area during the
cooler months. O'Shea et al. (in prep.) suggest that small dependent calves
may be restricted to traditional warm water sources by their mothers and
therefore avoid the cold induced mortality prevalent among subadults. The
lower St. Johns River constitutes marginal winter habitat for manatees
(Kinnaird and Valade 1983) and therefore may not be favored by females with
calves. Odell (1979) suggested that the tendency of calves to stay close to
their mothers might result in fewer calf sightings. It is possible that
calves, by virtue of their size and the tendency to associate closely with
their mothers, may have been oversighted in the turbid water characteristic
of the St. Johns River. However, many of the above studies reporting a high
percentage of calves have been conducted under turbid conditions. Also,
there are several reasons why calves are more likely to be seen (i.e.
synchronous breathing with their mothers and side-by-side traveling).
Therefore, I believe that the proportion of calves reported represents a
sound estimate.
Some authors (Moore 1951, Irvine and Campbell 1978, Shane 1981) have
suggested that a spring peak in calving may occur. Too few calves were
sighted in this study to indicate seasonal reproductive trends. The high
proportion of animals observed cavorting from April through June may indicate
a spring mating season; this is inconsistent with data presented by
Bengston (1981) who observed a greater percentage of cavorting and mating
behavior during the later summer and early fall in the upper St. Johns River.
Both studies indicate however that winter mating/cavorting is minimal which
suggests that mating occurs primarily in the warmer months.
Bengston (1981) estimated the manatee population of the entire St. Johns
River at 50-75 animals, a figure that Eberhardt (1982) states is not
consistent with the high mortality rate in the river and the increasing
numbers of manatees wintering in Blue Spring. I believe the effective
manatee population of the river (i.e. that population of animals that is not
necessarily resident but utilizes the river during part of the year) is much
greater than the above estimate. Manatee counts in the high thirties were
not uncommon during this study and a peak count of 48 animals was recorded
over three zones (6, 8 and 10) in one survey. Many animals probably move in
and out of the river during the warmer months and it is likely that these
counts reflect different individuals. Also, these figures represent relative
numbers and are most likely underestimates. Although daily survey conditions
did not influence manatee counts, turbid waters and limited visibility
throughout the duration of the study probably lowered the chance of sighting
manatees. Also, relative to the entire river, only a limited amount of
shoreline was surveyed for this study. Additional animals that winter at
Blue Spring remain south during the summer (Bengtson 1981) and very few could










have contributed to the numbers recorded in these surveys. Considering these
factors and the likely use of the river by many transient animals, it is
highly probable that the effective manatee population of the St. Johns River
is at least 150 animals.

The seasonal and weekend peaks observed in boat traffic are consistent
with data collected by Hanni (1978) showing that two-thirds of the
non-commercial boating activity in the Jacksonville area takes place from
July through September with most activity occurring over the weekends. These
high summer figures may be attributed, in part, to an influx of tourists from
outside the state (Bell et al. 1982). However, the majority of boats using
the St. Johns River are operated by residents within the northeastern region
of Florida (Bell et al. 1982).

Hanni (1978) also found that the number of boats with offshore
destinations was much less in the Jacksonville area than in areas farther
south (i.e. Dade Co. and St. Augustine) and attributed this to the fact that
tributaries and estuaries of the St. Johns River offer significant
alternative destinations for fishing and recreation. This may help explain
the high boat densities in Doctors Lake, the Ortega River and other zones
away from the mouth of the river. The majority of large recreational boat
traffic occurred near the mouth of the river (Mayport, zone 1). This
distribution is consistent with observations that the majority of boats
traveling offshore are typically larger than those remaining inland (Hanni
1978, Ditton et al. 1982). The distribution of recreational traffic is also
influenced by the distribution of docking facilities (Kinnaird 1983). The
high density of docking facilities in the Ortega River (zone 7) (where no
manatees were observed) and'the Mayport area (zone 1) may also concentrate
boating activity.

Commercial fishing and industrial traffic was distributed, as expected,
from the mouth of the river to Port Jacksonville, witf major concentrations
occurring near industrial plants, terminals and generating stations.
Although commercial fishing was determined to be the heaviest in zone 2, the
majority of commercial fishing boats was concentrated in zone 1 where the
unloading docks are located. Survey results may have been biased by the fact
that commercial fishing traffic, unlike other boat-class traffic, occur
primarily in the early morning and late evening, before and after the surveys
were conducted. In reference to manatees, zones 1 and 2 are the most
appropriate locations for commercial fishing vessels. By placing docks near
the ocean, the distance traveled on the river by vessels is minimized and the
probability of colliding with a manatee is reduced.
In general, the abundance, distribution or size class of boat traffic
did not appear to influence manatee distribution. However, the negative
correlation between manatee and boat counts in zone five, a zone
characterized by heavy industrial traffic suggests that manatees will avoid,
if possible, such areas when large, industrial craft are abundant. Also,
boat distribution and activity may have influenced manatee distribution
within zones of heavy traffic. Manatees tended to travel outside of boat
channels, avoid shoaled areas and restrict cavorting activities to sites with
low boat activity. In addition, the limited food and seasonal warm water
resources available to manatees and the distribution of these resources
within zones of high to moderate boat traffic, may not give manatees the
option of choosing alternative, low boat density zones.









Based on survey results, zones of major overlap between manatee and boat
use are Doctors Lake and Green Cove Springs (zones 8 and 10). These zones
therefore constitute areas of high manatee vulnerability to collisions with
boats and boating activity in these areas are a cause of concern. Data
collected by the Sirenia Project, FWS, Gainesville, Field Station, from 1976
to July 1983, on the distribution of manatee boat/barge mortality within this
study area, identify the industrial zones of the river (1,2,3 and 5) as the
zones of greatest conflict. Eighty-four percent (N = 16) of all boat/barge
related manatee deaths occurring within the study area (N = 19) were
recovered within these zones. The carcasses were severely mutilated (2
animals were cut almost entirely in half) and bore wounds of a size which
could only have been made by vessels with large propellers (Beck et al.
1982). Based on this fact, and the boat classes characteristic of these
zones, it appears that large industrial and commercial traffic is most likely
responsible for the majority of manatee boat/barge mortalities in the St.
Johns River. The narrow width of the river and the non-linear pattern of
traffic flow in these zones may also contribute to the problem (Kinnaird
1983). Other factors, such as the increased barge traffic during the winter
months when manatees aggregate at the power plants, may also augment the
problem. Although manatee boat/barge deaths occurred in all seasons in the
study area (O'Shea et al. in prep.), five of seven boat kills recovered in
the immediate vicinity of the power plants occurred during the cooler months
(Sirenia Project, unpubl. data). Animals traveling to and from food
resources to the south are extremely vulnerable to collisions with boats when
passing through this lower river conflict zone. Because animals ranging up
and down the entire east coast may frequent the lower St. Johns River, the
problem of boat/barge mortalities must be considered one of regional impact
(Kinnaird and Valade 1983).
Intracoastal Waterway (ICW)
Survey results from the Intracoastal Waterway support Hartman's (1974)
idea that this stretch of waterway is used by manatees primarily as a
migratory route along the east coast of Florida and south Georgia. This
northeastern section of the ICW is likely an important route between the St.
Johns River and Brevard County. These are the only two areas in northeast
Florida known to have significant numbers of manatees on a year-round basis
(Hartman 1974, Shane 1983). Manatees sighted during the surveys were almost
always traveling and observations were most frequent in the spring and late
fall, time periods that coincide with patterns of migration (Moore 1951,
Hartman 1974, 1979, Shane 1983, Rathbun et al. 1983). Increases in
manatee sightings in the ICW were generally staggered one month ahead of
increases in the number of sightings in the St. Johns River, supporting the
idea that manatees wintering outside the St. Johns may migrate to the river
from more southerly coastal regions during the spring via the ICW (Hartman
1974, Kinnaird and Valade 1983). The opposite pattern was not observed during
the fall, but the warm fall weather of 1982 may have caused a less well-
defined peak in movement. Long distance movements by manatees between the
St. Johns River and power plants on the ICW in Brevard and Broward Counties
(Rathbun et al. 1983, Kinnaird and Valade 1983) are also consistent with the
idea that the ICW is a major migratory route. Some migration may occur
through oceanic waters along the Atlantic coastline, but Hartman (1974) noted
that the four kilometer detour necessary to navigate the jetties at the mouth
of St. Johns River, the extreme shoaling and turbulent waters of some coastal












areas, and the lack of fresh water may discourage manatees from traveling
along the coast. It is likely that manatees utilize both the coastline and
the ICW, moving in and out between inlets. This would be consistent the
tendency for sightings to be clumped around inlets.
Data are also consistent with Hartman's (1974) observation that manatee
use of the ICW is limited by cold weather and by the lack of fresh water and
an adequate food supply. The occurrence and frequency of manatee sightings
generally decrease to the north. Manatee sightings are restricted to fewer
months of the year and peaks in sightings shift from spring to summer in the
more northern zones. Rathbun et al. (1982) noticed the same pattern of
manatee occurrence along the southeast coast of the U.S. north of Florida.
Fresh water run-off may be responsible for manatee concentrations in and
around Tomoka River and for other sightings near the confluence of fresh
water sources and the ICW, especially Spruce and Bulow Creeks. Food
resources become progressively scarcer north of Volusia County (Hartman 1974)
as do manatee sightings. The only manatees observed feeding in this study
were forced to forage on shoreline vegetation. Rathbun et al. (1982) also
cite limited food supply as a major factor restricting manatee movements up
the southeast coast of the U.S.
An exception to the northern decline in manatee observations throughout
the study area is found in the vicinity of Fernandina Beach (zone 1). The
warm water resources available to manatees from ITT Rayonier and the American
Container Corporation are responsible for the high spring counts in this
zone. Interestingly, Hartman (1974) did not observe manatees at these
outfalls during aerial surveys in 1974, nor were sightings reported by the
local residents interviewed. Industrial warm water outfalls have been cited
as being partly responsible for the recent expansion of the manatees winter
range up the northeast coast of Florida (Rathbun et al. 1983). Although
manatees were not observed at these warm water outfalls during the winter,
the plants appear to offer refuge for manatees during the cold snaps of early
spring and late fall, thereby possibly allowing manatees extended time to
range farther north during the summer months. A claim that manatees appear
at the Gillman Paper Company on the North River (zone 1) was not confirmed.
Of six cause-of-death categories defined for manatees salvaged statewide
(Bonde et al. in prep), dependent calf deaths are disproportionately high in
the northeastern section of the ICW (O'Shea et al. in prep.). O'Shea et al
interpret this to be largely a statistical result of lower boat mortality in
the area and lower calf mortality in other parts of northeastern Florida, but
also suggest it may reflect the use of quiet, shallow areas off the ICW as
birthing places by female manatees. The Tomoka River may be one such area
used by calving females. Complications or accidents during parturition may
account for many of these deaths (O'Shea et al.in prep.). Four of thirteen
(31%) perinatal and dependent calf deaths occurring from May 1976 through
July 1983 in the northeastern ICW were recovered in the Tomoka River (Sirenia
Project, unpubl. data). Although absolute numbers are not great, this is the
highest number of small calf deaths recorded for any river of similar size in
the state (Sirenia Project unpubl. data). The Tomoka River is also the site
of the only witnessed birth of a free-ranging manatee (McNerney 1982).
Although all tributaries were not surveyed in detail (due to overhanging
vegetation that often obscures isolated waterways), the extremely low
percentage of calves observed throughout the study does not suggest that
birthing is frequent elsewhere in the ICW.










Boat traffic in the ICW was consistently high throughout the year. This
may be due to the large number of small recreational boats that are able to
use the waterway year-round because of its sheltered nature and usually calm
waters (NOAA 1982).. An increase in traffic during the spring and summer is
attributed primarily to a rise in the number of larger recreational boats,
most likely operated by non-residents moving north and south with the
seasons.

Levels of boat traffic and boat density alone did not appear to be a
determining factor influencing large-scale manatee migration, travel or
distribution patterns. Areas of high manatee use overlapped with areas of
high boat density. Boat density was heaviest in the south, particularly in
the vicinity of Daytona Beach and Ponce de Leon Inlet (zones 7 and 8) and
near other inlets such as St. Augustine, Matanzas and the St. Johns River
that are utilized by manatees. High densities of large boats (i.e.
recreational boats 2 7.3 m long, tugs and commercial fishing boats), which
may pose greater threats to manatees than smaller boats (Beck et al. 1982),
were concentrated, near these inlets as predicted by Ditton et al. (1982).

At the local level, the effect of boat traffic and boat densities may be
more substantial. Manatees appeared to avoid heavy boat traffic within these
zones by traveling close to shore or by resting in oxbows or isolated
tributaries. A significant number of manatees were sighted in the Tomoka
River and associated bay and mosquito control canals relative to the rest of
the ICW. Manatees may use this tributary not only because of its fresh water
supply but also because of the very low density of boat traffic relative to
that in the portion of the ICW immediately adjacent.

Presently, manatee boat/barge mortality is extremely low in the ICW
relative to other areas on the east coast (O'Shea et al. in prep.). This may
be due to overall lower manatee numbers or, more likely, to the fact that
manatees in general do not spend much time in the waterway. However, an
increase in deep-draft vessels (i.e. tugs, barges and large recreational
boats) could be expected to increase boat/barge mortalities. The shallow
waters of the ICW do not provide sufficient room for a manatee to pass safely
underneath the hull of deep draft boats and the restricted canal width
through much of the ICW does not allow much leeway for escape in the event of
two boats passing simultaneously. Increased boat traffic may also limit
manatee movement up and down the east coast. Residents in Volusia county
claimed that increased boat traffic between the 1960's and 1970's was
responsible for a decline in manatee sightings (Hartman 1974).
Flagler County (zones 6 and 7) was the fastest growing county on the
east coast of Florida in the 1970's and a large portion of Florida's
burgeoning population is expected to continue to settle in Flagler County and
areas along the coast of the peninsula (Fernald 1981). Recreational and
commercial traffic are increasing throughout the northeastern ICW along with
the demand for docking facilities to accommodate these vessels (DNR 1983).
Such an increase will undoubtedly have a negative effect on manatees.
Therefore, wise marina siting policies and other management strategies
designed to protect manatees must be considered before the problem grows.
Finally, one critical question remains in the interpretation of the data
presented here: Is the manatee population in northeastern Florida declining?
One possible scenario is based on the following facts: 1) the low percentage












of calves in the St. Johns River and ICW relative to other areas, 2) the
number of boat/barge kills in the adult size class and 3) decreased winter
manatee counts at Brevard County power plants (Reynolds 1983). Taken
together, these facts translate into a textbook example of a declining
population. Chronic boat/barge mortality is occurring with more adults being
killed because of a top-heavy, unstable age distribution. Such an age
distribution has occurred because of the loss of a large number of subadults
from northeastern Florida in 1977 (O'Shea et al. in prep.) that would
normally have been recruited into the breeding population by the time of this
study. Therefore, less reproduction is seen relative to other regions
because the population is unstable and declining.
Another possible, but less likely scenario, is that the population is at
its greatest possible size given the available resources. Reproduction is
suppressed and the population is stable but top-heavy with adults. Because
manatees would no longer be reproducing as quickly as a population at a size
lower than carrying capacity, boat/barge deaths would be biased towards
adults and the percentage of calves in the population would be low relative
to other areas.

It is also possible that avoidance of northern regions by females with
young may influence low calf counts. Shifts in the use of Brevard County
power plants by manatees could also describe other scenarios. However, I
believe that until the population status of manatees in northeastern Florida
is better understood, we must err conservative and develop management
policies and strategies for northeastern Florida that deal with a potentially
declining population.









Management Recommendations

1) It would be prudent to continue aerial surveys for manatees with an
intensity equal to this study to better understand the spatial and
temporal patterns of manatees in northeast Florida, to gain
knowledge about the annual variation of these patterns and to help
determine if regional populations are declining.
2) Formal agreements should be drawn up between industry officials and
the USFWS Manatee Coordinator to begin or to continue monitoring
and photographing individual manatees frequenting the Jacksonville
and Fernandina Beach power and industrial plants. Consideration should
also be given to the initiation of a program to tag and radio-track
summer aggregations in the St. Johns River. Such programs would help
increase knowledge of manatee movements up and down the east coast.
3) Signs warning boaters of manatee presence and where to call in the event
of a dead manatee should be installed at all marinas, fish camps and
boat ramps throughout the lower St. Johns River and the ICW in
northeastern Florida. Locations of particular importance for posting
are Doctors Lake, the grassbeds near Green Cove Springs, the
Jacksonville and Fernandina Beach industrial and power plants and inlets
along the ICW. Informational and educational material should be
distributed to all marinas and fish camps in the study areas. This task
could be accomplished by the Coast Guard Auxillary, local Boy Scout
troops or volunteer groups and should be organized by the USFWS Manatee
Coordinator.


4) Efforts should be made to limit boating facilities and dredging
activities in the Doctors Lake/Green Cove Springs area until more
information is available on the importance of this area to manatees.
Boating facilities should also be limited in and around Tomoka
River and other shallow fresh water tributaries in the ICW thought
to be important to manatees. Facilities for larger, deep-draft boats
(i.e. commercial fishing vessels and off-shore recreational boats
> 7.3 m long) should be located as near as possible to inlets in order
to minimize the distance traveled through manatee habitat to the ocean.
5) Tomoka State Park should be given status as a summer sanctuary zone
for manatees. The size class of boats entering the state park waters
should be limited to those less than 7.3 m in length and idle
boat-speed zones should be established. Other state and federal
lands bordering waterways used by manatees should include
considerations for manatees in their management plans. State and
Federal lands included within these study areas are: Cumberland
Island National Seashore, Fort Clinch State Park, Castillo de
San Marco National Monument, Frank B. Butler State Recreation Area,
Fort Matanzas National Monument and Flagler Beach State Park.
6) Manatee populations at Brevard County power plants should be monitored
in the winter and possibly elsewhere in Brevard County during the
summer. This may be a critical step towards understanding whether the
population of manatees in northeastern Florida is presently declining
and is essential in documenting long distances movements by animals
from the St. Johns River and ICW that may winter in Brevard County.








52


7) The research and management responsibilities of local, state and
federal agencies should be integrated and coordinated. This could
be accomplished while drafting plans for the siting of marinas, the
control of boat traffic, the reduction of manatee mortality and
harassment, the protection of grassbeds and critical resources and other
issues such as weed control and sewage disposal.












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packard f ac s e of
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d416000-44 a Research
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Ii -" .'


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