Distribution and abundance of the West Indian manatee Trichechus manatus around selected Florida power plants following winter cold fronts: 1984–1985

Biological Conservation 38 (1986) 103 113

Distribution and Abundance of the West Indian Manatee Trichechus manatus around Selected Florida Power Plants following Winter Cold Fronts: 1984-85

John E. Reynolds, III Eckerd College, St Petersburg, Florida 33733, USA

& J. Ross Wilcox Environmental Affairs, Florida Power and Light Company, PO Box 14000, Juno Beach, Florida 33408, USA

A B S T R A CT Ten one-day aerial surveys were conducted in winter, 1984-85, to assess manatee distribution and abundance around)qve Florida Power & Light Company (FPL) plants: Cape Canaveral (PCC), Riviera (PRV), Port Everglades (PPE), Lauderdale (PFL) and Fort Myers (PFM). A total o f 3804 manatees was observed, with a maximum o f 636 animals for a single survey. Individual surveys for 1984 85 produced higher combined counts for all plants than in previous years. Maximum counts for PRV, P P E and P F M were the highest recorded.['or those particular plants. The maximum count .for P C C in 1984-85 was lower than counts .from most previous years, and the maximum f r o m PFL was intermediate, relative to maxima f r o m previous years. The counts along the east coast of Florida probably reflected a southward redistribution o[" manatees as well as very cold January weather after warm December conditions. The high count at P F M probably resulted j r o m cold January weather and sur['ace resting behaviour by the manatees which made them more visible than usual. Calves represented 10"3% o f the animals observed near the FPL plants and in Hobe Sound. P F M had a higher percentage o f calves than did other plants. 103

Biol. Conserv. 0006-3207/86/$03"50 ~', Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain

104

John E. Reynolds III, J. Ross Wilcox

INTRODUCTION Aerial surveys have been an economical means by which to assess the abundance and distribution of West Indian manatees Trichechus manatus in Florida since the mid-1970s (see, for example, Irvine & Campbell, 1978; Shane, 1983; Kinnaird, 1985; Reynolds & Wilcox, 1985). The current study represents the eighth consecutive year in which aerial surveys have been conducted around selected Florida Power & Light Company (FPL) plants. Due to their consistent methodology, these surveys possess considerable value in terms of long-term assessments of manatee regional abundance. This study assessed distribution and abundance of manatees around five selected FPL plants following passage of cold fronts in winter 1984-85, and compared these findings to similar data from previous years.

METHODS Following passage of severe or prolonged cold weather in Florida, aerial surveys were initiated. Surveys were conducted from a high-winged Cessna 172 or 172RG aircraft. Cruising altitude and air speed were 152 m and 167 km h - a, respectively. During circling of manatee aggregations, slower air speeds and lower altitudes were used to permit more efficient counting. Photographs were taken to verify visual counts. Aerial surveys were flown on the following dates: 6, 10, 14, 19, 22 and 27 January and 2, 9, 15 and 18 February 1985. Each flight lasted one day. Surveys focused on five power plants, listed in the order in which they were surveyed: Cape Canaveral Plant (PCC), Riviera Plant (PRV), Port Everglades Plant (PPE), Lauderdale Plant (PFL), and Ft Myers Plant (PFM). Waters within about 8 k m of each plant (termed the vicinity of the plant) were also observed for manatees. Finally, extended areas of the Intracoastal Waterway exist between plants, and these areas, especially Hobe Sound, were also surveyed. Certain data were routinely recorded: total manatees present; total calves (defined as animals less than half the length of a closely associated animal) present; distribution of animals; behaviour, including feeding or direction of travel; weather and water conditions. Daily air temperatures for each location were obtained from the National Climatic Data Center. Daily water temperatures for each

Manatee distribution and abundance

105

power plant were provided as available by the individual plants. Air and water temperature data used for PRV were also applied to nearby Hobe Sound.

RESULTS

Cape Canaveral Plant (PCC) and vicinity Manatees were sighted in the vicinity of PCC on 9 of 10 flights, with a high count of 34 being recorded on 19 January (Table 1). The percentage of animals that were calves was 9.7%. Survey conditions were generally poor or fair, especially in the effluent area of the Orlando Utilities (OUC) plant (approximately 4 km north of PCC) where foamy, opaque water made accurate counting difficult. Most of the animals observed were apparently bottom-resting, although behaviour was difficult to determine due to poor visibility. Mean monthly air temperatures in the PCC area were 1.7°C warmer than normal for December 1984, 3.8~'C colder than normal for January 1985, and normal for February 1985 (Anon., 1984; unpublished data from the National Climatic Data Center).

Hobe Sound Manatees were observed in Hobe Sound every flight except 22 January. The maximum count was 67 animals, and the percentage of the animals observed that were calves was 13.0% (Table 1). The animals exhibited two main behaviours: resting or active swimming north-south along the central channel of the Intracoastal Waterway.

Riviera Plant (PRV) and vicinity Manatees were seen at PRV on every flight, with a maximum count of 231 on 22 January. The mean count per survey was almost 83, and the percentage of the animals observed that were calves was 9.2% (Table 1). Survey conditions were generally good to excellent. Animals in the vicinity of PRV usually bottom- or surface-rested, especially in the protected area of the Intracoastal Waterway where Unit 2 of the plant discharged warm water. Animals rarely occupied the middle channel of the Intracoastal Waterway. Mean monthly air temperatures near PRV

106

John E. Reynolds III, J. Ross Wilcox

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20 30 62 144 109 234 28 23 190 I I6 956

85 85 85 85 85 85 85 85 85 85

85 85 85 85 85 85 85 85 85 85

85 85 85 85 85 85 85 85 85 85

6 Jan. IO Jan. 14 Jan. 19 Jan. 22 Jan. 27 Jan. 2 Feb. 9 Feb. 15 Feb. 18 Feb. Total

6 Jan. IO Jan. 14 Jan. I9 Jan. 22 Jan. 27 Jan. 2 Feb. 9 Feb. I5 Feb. 18 Feb. Total

6 Jan IO Jan. I4 Jan. I9 Jan. 22 Jan. 27 Jan. 2 Feb. 9 Feb. I5 Feb. I8 Feb. Total

PPE

PFL

PPM

(2) (4) (5) (14) (11) (17) (4) (1) (12) (7) (77)

(3) (21) (5) (76)

(I) (3) (0) (0) (2) (1) (8)

(14) (28) (IO) (37) (18) (15) (12) (8) (16) IO0(9) I 359 (167)

93 I41 80 338 136 139 99 70 163

5 29 4 2 10 8 70

I (0) 0 (0) II (1)

0 (0)

28 I91 85 829

9 Feb. 85 I5 Feb. 85 18 Feb. 85 Total 16.8 17.4 15.8 19.1 Il.7 15.7 23.5 18.7 12.3 15.4

16.8 17.4 15.8 19.1 II.7 15.7 23.5 18.7 12.3 15.4

15.9 16.5 13.3 18.2 9.1 IS.2 23.5 15.7 10.6 16.5

14.4 17.2 17.5 17.2 4.4 13.1 25.6 IS-3 13.1 19.2

14.4 17.2 17.5 17.2 4.4 13.1 25.6 15.3 13.1 19.2

13.3 16.7 16.1 17.2 5.6 12.8 24.4 15.0 8.9 18.9

Good Fair Fair Good Fair Good Good Good Excellent Poor

Fair Fair Poor Fair Fair Fair Fair Fair Good Poor

Poor Fair Fair Very good Fair Fair Very poor Fair Poor Fair

IO.0 13.3 8.1 9.7 IO.1 7.3 14.3 4.4 6.3 6.4 8.1

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20.0 12.5 I I.4

9.1 20.0 IO.4

16.8 IO.6 15.0

14.4 Il.1 17.8

Good Excellent Very good

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19.5 19.0 17.0 18.0 21.0 21.3 21.5 18.5 20.0 21.0

NA NA NA NA NA 26 I NA 17.8 21.1 21.7 NA NA

20.3 18.8 17.7 17.7 20.3 22.5 22.0 20.7 21.0 20.7

21.7 NA NA

NA 26.1 NA 17.8 21.1

22.2 21.7 21.8 21.7 21.3 20.7 21.7 22.4 21.1 21.1

21.9 20.9 20.9

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108

John E. Reynolds III, J. Ross Wilcox

were 2.3°C warmer than normal for December 1984, 2.5°C colder than normal in January 1985, and 0.9°C warmer than normal for February 1985 (Anon., 1984; unpublished data from National Climatic Data Center).

Port Everglades Plant (PPE) and vicinity Manatees were observed at PPE on all surveys, with a mean count per survey of nearly 100 animals. The maximum count occurred on 27 January, when 234 manatees were observed. The percentage of calves was the lowest among the plants: 8.1% for all surveys (Table 1). Survey conditions were good. Usually, manatees bottom-rested along the banks of the effluent channel. Mean monthly air temperatures for the Fort Lauderdale area (where Port Everglades is located) were 2.3°C warmer than normal in December 1984, 1.9°C colder than normal in January 1985, and 0.4°C warmer than normal in February 1985 (Anon., 1984; unpublished data from National Climatic Data Center).

Lauderdale Plant (PFL) and vicinity Manatees were observed at P F L on 8 of 10 surveys, with a maximum count of 29 animals (Table 1). Calves represented 11.4% of the animals observed (Table 1). Resting and feeding were the main behaviours observed. Survey conditions were fair at PFL. Mean monthly air temperatures for P F L in winter 1984-85 were the same as reported for PPE and vicinity.

Fort Myers Plant (PFM) and vicinity Manatees were sighted at P F M on every survey, with a mean count per survey of over 135. The maximum count of 338 animals occurred on a relatively warm day when the manatees were surface-resting, perhaps basking in the sun. The percentage of calves was the highest among the power plants: 12.3% (Table 1). The animals were generally resting or cruising. Survey conditions were fair to poor at PFM. Mean monthly air temperatures in Fort Myers were 2.6°C warmer than normal for December 1984, 1.6°C colder than normal for January 1985, and 1.6°C warmer than normal for February 1985 (Anon., 1984; unpublished data from National Climatic Data Center).

109

Manatee distribution and abundance

TABLE 2 Number of Manatees Observed During Aerial Surveys in Winter 1984-85 (The number of calves is enclosed in parentheses and included in the total number of animals for each category.) Survey data

Manatees at FPL plants and Hobe Sound

Manatees not at FPL plants

Total

6 January 1985 10 January 1985 14 January 1985 19 January 1985 22 January 1985 27 January 1985 2 February 1985 9 February 1985 15 February 1985 18 February 1985 Total Mean/flight Per cent calves

143 (20) 224 (37) 190 (22) 597 (64) 488 (48) 550 (49) 227 (29) 129 (12) 586 (53) 331 (23) 3465 (357) 346.5 10.3

34 (5) 44 (7) 39 (3) 31 (3) 26 (2) 29 (5) 48 (6) 16 (1) 50 (4) 22 (1) 339 (37) 33.9 10.9

177 (25) 268 (44) 229 25) 628 67) 514 50) 579 54) 275 35) 145 13) 636 57) 353 24) 3 804 394) 380.4 104

Collective data

A total of 3804 manatees was observed during aerial surveys conducted in winter 1984-85, with 3465 animals being found in the vicinity of the five F P L plants surveyed and in Hobe Sound (Table 2). The 394 calves observed represented 10.4% of all manatees sighted, and the percentage of calves observed at the F P L plants (10.3%) was slightly lower than the percentage observed elsewhere (10'9%). The mean number of animals sighted per survey was 380 (range = 145-636 manatees; see Table 2).

DISCUSSION Aerial surveys conducted during the winter of 1984-85 produced higher counts of manatees a r o u n d Florida Power & Light C o m p a n y power plants than have similarly conducted surveys in the past, and the highest counts on record occurred at PRV, PPE, and P F M in winter, 1984-85 (Table 3). Conversely, PCC and vicinity continued to produce low

110

J o h n E. R e y n o l d s III, J. R o s s W i l c o x

TABLE 3 Maximum Number of Manatees Sighted During an Individual Survey at Five FPL Plants and in Hobe Sound During Each of the Past Eight Years Site

PCC/OUC PRV HS PPE PFL PFM All 5

power plants Data from from from from from from

b Data c Data d Data e Data : Data

Survey year 197778 a

197879 a

197980 a

198081 b

198182 c

198283 d

198384 e

198485 y

125 68 56 114 36 271

113 99 97 125 27 172

116 108 38 86 36 142

138 102 39 110 52 136

136 168 35 57 19 127

15 98 19 56 16 85

20 60 28 35 11 122

34 231 67 234 29 338

614

536

488

538

507

270

248

866

Rose & McCutcheon (1980). Raymond (1981). McGehee (1982). Reynolds (1983). Reynolds (1984). this report.

counts of manatees, and PFM had a maximum count in 1984-85 that was intermediate compared to previous years' counts. The PFM produced the largest aggregation o f manatees on record on 19 January 1985:338 animals. This observation occurred in the afternoon on a relatively warm day when water conditions were better than usual for observation around PFM, and when the manatees themselves were easily seen as they surface-rested, perhaps in an effort to absorb solar radiation to counter the effects of cold water. The previous high count of 271 manatees, which also occurred at PFM in 1977-78 (see Table 3), took place under similar conditions to those just described (P. Rose, pers. comm.). High counts at PFM were not restricted to times when the manatees were especially visible due to their behaviour. The mean count per survey was 136 manatees (Table 1), a figure equal to or higher than the maximum counts for the previous 4 years (Table 3). It is likely that manatees sought shelter at the plant in great numbers because they had acclimatised to relatively warm weather during the previous two winters (Reynolds, 1983, 1984) and during December 1984, so that the intense

Manatee distribution and abundance

111

cold of January 1985 induced more animals than usual to seek refuge. No significant correlations were found between manatee abundance at P F M and either air or water temperatures (Reynolds, 1985). Another plant which had very high numbers of manatees in winter 1984-85 was PRV. This plant has historically produced large numbers of manatees in winter (Table 3). The record count of 231 manatees on 22 January 1985 may have resulted because (1) the manatees acclimatised to the warm December weather, or even to the warmer than usual weather from the previous two winters (Reynolds, 1983, 1984), and then reacted to the January intense cold by aggregating in larger numbers than usual; and (2) the intense January cold induced manatees from Brevard County that would ordinarily aggregate at PCC or OUC to migrate south to PRV or even to PPE. Shane (1983) and Packard (1981) have documented such winter movements by Indian River manatees. High discharge temperatures (averaging l l . I ° C above ambient on 22 January) produced in the protected region of the Unit 2 discharge at PRV may have provided added inducement for manatees to seek refuge there during very cold weather. Manatee abundance at PRV was significantly correlated with ambient air and water temperatures, both on survey dates and on survey days plus the previous two days (Reynolds, 1985). The final plant which produced unusually large aggregations of manatees in 1984-85 was PPE (Table 3). As discussed above for PRV, the redistribution of manatees from the Indian River, as well as the response of manatees around PPE to warm weather followed by intense January cold, probably explains the great manatee abundance at PPE. More thorough surveys in 1984-85 may also explain the high counts, since more circling time was allowed for the 1984-85 surveys by air traffic controllers at Ft Lauderdale International Airport. Manatee abundance at PPE was correlated with ambient water temperatures (Reynolds, 1985). Relatively low manatee abundance in the vicinity of PCC has been mentioned, and a possible explanation offered that during the intensely cold January that winter, Brevard County manatees responded by migrating southward to PRV and PPE. Low counts at PCC and vicinity may also reflect the poor water visibility throughout the area, especially at OUC, and the morning bottom-resting behaviour of the manatees. Similar to PCC, P F L did not produce large aggregations of manatees in 1984-85. The count at PFL was about normal, compared to counts from previous years (Table 3), a result that is not surprising given the

112

John E. Reynolds III, J. Ross Wilcox

sporadic operational schedule of the plant. Manatee abundance at PFL was not related to ambient water or air temperatures (Reynolds, 1985). Calves, in 1984-85, represented 10.3% of the animals sighted around FPL plants and Hobe Sound, and calves represented 10.4% of all manatees sighted (Table 2). Previous surveys found that calves represented as little as 9.0% of the animals sighted (Rose & McCutcheon, 1980) or as much as 13.4% of the total (Raymond, 1981). For the third consecutive year, PFM had the highest percentage of calves of any power plant, and PPE had the lowest percentage (Table 1; for previous years' data see Reynolds, 1983; 1984). The Ft Myers Plant, in particular, may have special importance to manatees as a refuge for females with calves. The differences in manatee abundance and distribution during winter 1984-85 serve to underscore the importance of the long-term perspective for scientists trying to understand and predict manatee behaviour patterns, as well as for power plant officials who wish to provide sufficient warm water to prevent locally high manatee mortality. The aerial surveys of power plants represent one of the few long-term data bases, and their value is increased with every survey year.

A C K N O W L E D G E M ENTS This research was supported by Purchase Order 01249-87331 from Florida Power & Light Company to Reynolds. FPL plant personnel provided water temperature data used in this report, and air temperatures were supplied by the National Climatic Data Center, Asheville, North Carolina. We also appreciated the help of J. Packard, G. Rathbun, T. O'Shea, P. Rose, and K. Frohlich, all of whom provided advice or information during the study. Finally, we thank the pilots of Topp Air for their services and the Air Traffic Controllers at Ft Lauderdale International Airport and other Florida coastal airports for their patience and cooperation.

REFERENCES Anon. (1984). Climatological data Florida December 1984. NOAA, Environmental Data and Information Service, 88(12), 21 pp.

Manatee distribution and abundance

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Irvine, A. B. & Campbell, H. W. (1978). Aerial census of the West Indian manatee, Triehechus manatus, in the southeastern United States. J. Mammal., 59, 613 17. Kinnaird, M. F. (1985). Aerial census of manatees in Northeastern Florida. Biol. Conserv., 32, 59-79. McGehee, M. A. (1982). Manatees (Trichechus manatus): Abundance and distribution in and around several Florida power plant effluents during the winter of 1981-1982. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 31534-86419. Packard, J. M. (1981). Behavioral factors influencing winter census of manatees (Trichechus manatus) in Palm Beach Count),, Florida. US Fish and Wildlife Service, Atlanta, Contract No. 14-16-004-00-105. Raymond, P. W. (1981). Manatees (Trichechus manatus): Abundance and distribution in and around several Florida power plant effluents. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 3153+ 8251 I. Reynolds, J. E., III (1983). Distribution and abundance of West Indian manatees (Trichechus manatus) around selected Florida power plants following winter cold fronts. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 71527-88609. Reynolds, J. E., III (1984). Distribution and abundance Of West Indian manatees (Trichechus manatus) around selected Florida power plants following win ter cold fronts: 1983 1984. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 01249-83562. Reynolds, J. E., III (1985). Distribution and abundance of West Indian manatees (Trichechus manatus) around selected Florida power plants /bllowing winter cold fronts. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 01249-87331. Reynolds, J. E., Ill & Wilcox, J. R. (1985). Abundance of West Indian manatees (Trichechus manatus) around selected Florida power plants following winter cold fronts, 1982 1983. Bull. Mar. Sci., 36, 413 22. Rose, P. M. & McCutcheon, S. P. (1980). Manatees (Trichechus manatus): Abundance and distribution in and around several Florida power plant effluents. Final Report, Florida Power and Light Co., Juno Beach, Contract No. 31534-86626. Shane, S. H. (1983). Abundance, distribution and movements of manatees (Trichechus manatus) in Brevard County, Florida. Bull. Mar. Sci., 33, 1 9.