Aerial Surveys of Florida manatees in Charlotte County, 1997/98 DEP Contract # MR219. September 2, August 31, 1998

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1 Aerial Surveys of Florida manatees in Charlotte County, 1997/98 DEP Contract # MR219 September 2, August 31, 1998 SUBMITTED TO: Division of Marine Resources Bureau of Protected Species Management Florida Department of Environmental Protection SUBMITTED BY: Jessica K. Koelsch, Mote Marine Laboratory October 29, 1998 Mote Marine Laboratory Technical Report No. 595 Introduction Aerial surveys provide information on manatee spatial distribution, relative abundance, and seasonal habitat use. They provide an important monitoring tool for management purposes and can be used to identify high-use areas, estimate seasonal and regional densities, and detect trends in counts (Ackerman, 1995). The Contractor has conducted aerial surveys in the Sarasota area waters since 1985, including southern Manatee County ( ), Sarasota County (1987-present), and northern Charlotte County ( ) (Kadel and Patton, 1992; Koelsch and Pitchford, 1998). Long-term data sets such as these provide valuable information on trends in distribution and relative abundance (Ackerman, 1995). In addition, Ackerman (1995) recommended updating aerial survey data every five years. Charlotte County, Florida has been recognized as an important area for manatees since the 1940s (Moore, 1951). Between , numerous naturalists, fishermen, and residents reported manatees in the Charlotte County waters including the Myakka River, Placida Harbor, Charlotte Harbor north of Pine Island, and Lemon Bay (Moore, 1951). This area was considered to be the ordinary northern limit of manatees' winter range along the west coast, although they were presumed to move farther north in the summer. Subsequent aerial surveys in the 1970s also documented manatees wintering in the region (Irvine and Campbell, 1978; Hartman, 1979). Since the 1970s, other investigations have provided additional information on manatee distribution, abundance, density, and habitat use within Charlotte County waters (Ackerman, 1995; FDEP, 1997; Koelsch and Pitchford, 1998). Current information on manatee abundance and distribution is critical in developing management strategies. Presently, a Charlotte Harbor seagrass and manatee protection task force is developing natural resource protection zones. Manatees in Charlotte County waters have not been routinely surveyed since 1991 (Kadel and Patton, 1992) and 1988 (Ackerman, 1995; Koelsch and Pitcij,ford, 1998). During 1997/98, Mote Marine Laboratory (MML) surveyed Charlotte County waters, updating the data from 1987/91. With additional data on regional distribution in southwest Florida,

2 resource managers can identify sites of high manatee density, and focus protection efforts at those sites. In addition, aerial surveys can enhance photographic identification studies by directing research vessels to groups of manatees, facilitating collection of other ecological and behavioral data on individual manatees. Methodology Using standard aerial survey methodology (Irvine and Campbell, 1978; Ackerman, 1995), we surveyed manatees in the inshore and near-shore waters of Charlotte County following an established general flight path (Figure 1). One experienced primary observer (Yves Delpech) occupied the front right seat of the survey aircraft and, on most flights, a second observer occupied the rear right seat (Table 1). Secondary observers assisted with verifying counts, watching the water when the primary observer was recording data, and communicating with any photographic identification boat crews in the survey area. Aerial survey teams operated at a 150- m typical altitude and 130 kmihr typical air speed, most often with an experienced pilot in a single engine Cessna with the right window open. We used a Lake Amphibian aircraft for three flights (Table 1). Individual flights lasted hours (x= 5.2), however hours (x= 7.1) were required to complete the entire survey (sometimes over multiple days). Several flights were aborted because of poor conditions and high cloud cover, and were resumed on a subsequent day. Several surveys early in the study were conducted during mostly cloudy weather. Weather conditions improved during later flights. The primary observer plotted manatee sightings on photocopied base maps from the Atlas of Marine Resources (FDEP, 1997), including Florida shoreline with bathymetry and aids to navigation added. The observer noted number of adults and calves (one-half the size of a closely-associated adult; Irvine and Campbell, 1978), behavior, direction of travel, and time. During most non-winter flights (March - November), the aerial observer also coordinated with boat-based photo-identification teams in conjunction with contract MR-226. The primary observer entered manatee sighting locations into a geographic information system (GIS), ArcView 3.0 and associated dbase files; a secondary observer verified and. corrected data. Results From September 1, 1997 to August 31, 1998, MML observers completed 24 aerial surveys during 33 different flights (Table 1). Approximately two surveys were completed per month. We completed three surveys in June 1998 to compensate for conducting only one survey in May. In addition, survey conditions during the November 12, 1997 flight were unacceptably poor and this flight was repeated on November 19; data from the November 12 flight are not reported. Manatees were counted on every survey (x = 63.8, range 1-220; Figure 2). Counts of adults and calves per flight ranged from (x = 59.6) and 0-21 (x = 4.2), respectively. Within the 649 groups of one or more manatees, 1,531 individual manatees were counted including 1,431 adults and 100 calves. Manatees were observed throughout Charlotte County waters (Figure 3). Many large groups were located in Turtle Bay, along the west shore of Charlotte Harbor, at the mouth of the Peace River, and along the east shore of Charlotte Harbor outside Pirate's Cove (Figure 3). Group size (x = 2.4 individuals/group) ranged from 1 (n = 337 groups) to 4 = 1 group) with most individuals observed alone (Figure 4). Manatee sightings varied seasonally with fewest manatees in winter (December - February) and most in spring (March - May) and summer 2

3 (June - August; Figure 2). Site use by manatees also varied seasonally (Figure 5). Fall (September - November) manatee sightings occurred mainly in the Placida and Gasparilla areas and the east side of Charlotte Harbor. During the winter, manatees used primarily canal systems in Port Charlotte, Punta Gorda, and Burnt Store Marina as well as the Peace River. During the spring, manatees were observed frequently off Pirate's Cove and in Turtle Bay. During the summer, manatees dispersed throughout Charlotte County waters, especially Lemon Bay, Turtle Bay, the Myakka River, and the Peace River. Behaviors were recorded for 603 of the sightings or groups. Manatees were observed most often traveling (n = 211; 35.0%), resting (n = 204; 33.8%), and milling (n = 136; 22.6%). They were less frequently observed mating (n = 4; 0.7%), socializing (n = 21; 3.5%), and feeding (n = 27; 4.5%). During the entire study, 100 calves were observed in 85 groups (range 0-4 calves/group); 6.5% of all manatees observed were calves. Most often only one calf was observed per group (n = 74 groups); however, three calves were observed in groups within Bull Bay (near Turtle Bay) and off Pirate's Cove, and four calves were in one group in the Myakka River (Figure 6). Calves occurred most often in Turtle Bay, the Peace River, and off Pirate's Cove as well as Lemon Bay, to a lesser extent (Figure 6). Most calves were counted between late April and early July with a maximum count of21 calves on June 22, 1998 (Figure 2; Table 1). Aerial observers coordinated and directed photographic identification boat crews to groups of manatees during 17 flights, in conjunction with contract MR-226. Boat-based crews concentrated in areas where manatees were consistently observed, such as Turtle Bay and Burnt Store Marina during October July 1998 and in Lemon Bay during August Although manatees frequently occurred in the Myakka and Peace Rivers, dark tannin-stained waters impeded boat-based observations. Discussion Manatees used the waters throughout Charlotte County regularly and year-round, with seasonal shifts in relative abundance and regional distribution. For example, numerous individuals, groups, and calves were sighted repeatedly at several locations that appeared especially important for manatees. Seasonally, fewer manatees used the area during the winter (December - February) compared to other warmer months. In addition, manatees may emphasize their use of different areas at different times of the year. Seasonal shifts were probably based on water temperatures, with manatees seeking warmer waters (above 20 C) in the cooler months (Irvine, 1983). Although many individuals may have left the region in search of thermal refugia elsewhere, winter manatee sightings in canals and basins suggested a few manatees used local, deep-water, minor aggregation sites, as observed elsewhere in the state (USFWS,.1995). These findings share both similarities and differences with previous studies. Aerial surveys conducted in the mid/late 1970s and 1980s indicated year-round manatee use of Charlotte County waters with seasonal shifts (Irvine and Campbell, 1978; FDEP, 1997). Similar to 1997/98 results, aerial surveys conducted in 1987 and 1988 in a similar region counted fewer manatees during the winter and more in April- July (FDEP, 1997). Observed patterns of regional distributioit'r behaviors, and group sizes were also similar between the two studies (FDEP, 1997). However, other findings differed between the two studies. Total counts were greater in the more recent 3

4 study compared to ten years earlier (x = 63.8 vs. x = 37.1 manatees/flight). In addition, a smaller percent of calves (6.5%) was observed in 1997/98 versus 1987 and 1988 (10.3%). Although aerial surveys reveal much about regional manatee abundance and distribution, they possess several biases (Ackerman, 1995; Lefebvre et ai., 1995). Unknownproportionsofrnanateesare missed; however, it is impossible to estimate a confidence interval for anyone survey (Lefebvre et al. 1995). Manatees may be missed by observers or may be difficult to spot when they are submerged in murky waters (Lefebvre et ai., 1995). Poor weather conditions and cloud cover also hamper an observer's ability to spot manatees. In addition, the number of manatee5 observed is dependent on observer effort and experience and degree of survey coverage. Therefore, counts from aerial surveys represent the minimum number of manatees in a region and differences between current and previous studies should be viewed cautiously. Despite these limitations, resource managers planning manatee conservation strategies routinely use data from aerial surveys. For example, manatee protection measures are typically focused at areas of recurring manatee use and the travel corridors linking them. Higher observed counts compared to previous years may be indicative of greater manatee use within the region resulting from immigration and/or population increase. Alternatively, lower percent of calves may indicate a decrease in reproduction. Continued surveys of the area can support findings within the Charlotte County area and may substantiate trends in counts and calf percentages. Literature Cited Ackerman, B.B Aerial surveys of manatees: a summary and progress report. Pages in O'Shea, T.1., B.B. Ackerman, and H.F. Percival (eds.). Population biology of the Florida manatee. NatI. BioI. Servo Inf and TechnoI. Rep. 1. Ft. Collins, CO. 289pp. Florida Department of Environmental Protection (FDEP) Florida Marine Research Institute Atlas of Marine Resources, Version l.l. Garrott, R A, B. B. Ackerman, 1. R Cary, D. M. Heisey, 1. E. Reynolds III, P. M. Rose, and 1. R WIlcox Trends in counts of Florida manatees at winter aggregation sites. Journal of WIldlife Management 58: Hartman, D. S Biology and behavior of the manatee (Trichechus manatus) in Florida. Special Publication No.5. Am. Soc. of Mammal. 153 pp. Irvine, A B Manatee metabolism and its influence on distribution in Florida. BioI. Conserv.25: Irvine, A B. and H. W. Campbell Aerial census ofthe West Indian manatee, Trichechus manatus, in the southeastern United States. Journal of Mamma I. 59(3): KadeL J.1., and G.W. Patton Aerial studies of the West Indian manatee (Trichechus manatus) on west coast of Florida from : A comprehensive six year study. Mote Marine Laboratory Technical Report No pp. Koelsch, J.K. and T.O. Pitchford Florida manatees (Trichechus manatus iatirostris) in Charlotte Harbor. Pages in Treat, S.F. (eds.). Proceedings ofthe Charlotte Harbor Public Conference and Technical Symposium; March, 1997; Punta Gorda, Fla. Charlotte Harbor National Estuary Program Technical Report No West Palm. Beach (Fla.); South Florida Management District 274pp. 4

5 Lefebvre, L. W., B. B. Ackerman, K. M. Portier, and K. H. Pollock Aerial survey as a technique for estimating trends in manatee population size--problems and prospects. Pages in O'Shea, T.J., B.B. Ackerman, and H.F. Percival (eds.). Population biology of the Florida manatee. Nati. BioI. Servo 1m. and Technoi. Rep. 1. Ft. Collins, CO. 289pp. Moore, J. C The range of the Florida manatee. Quarterly Journal of the Florida Academy of Science 14:1-19. U.S. Fish and Wildlife Service (USFWS) Florida Manatee Recovery Plan, Second Revision. U.S. Fish and Wildlife Service, Atlanta, GA. 160 pp. 5 ".

6 Table I. Charlotte County manatee aerial survey activity, September 2; August 31, Flight Survey End Total Aircraft Primary Secondary Date Start Time F li ht Hrs Type Observer Observer Adults Calves Total G[S Notes 10-Sep-97 9:20 16: Cessna 172 Y. De[pech 1. Koelsch Y Partly cloudy, became overcast; overall fair conditions. 18-Sep-97 9:48 17: Cessna 172 Y. Delpech T. Pitchford Y Overcast but not dark; fair conditions. 6-0ct-97 10:10 15: Cessna 172 Y. Delpech none 10 II Y Good conditions deteriorated to poor (wind and clouds). J 30-0ct-97 9:55 13: Lake Amphibian Y. Delpech 1. Koelsch Y Fair deteriorated to poor; flight aborted; resumed Nov-97 9:40 13: Lake Amphibian Y. Delpech 1. Koelsch - Continuation of 10/30 flight; fair-good conditions. 12-Nov-97 8:49 15: Cessna 172 Y. Delpech none Y Poor conditions; not included in data set; will resurvey. 19-Nov-97 8:47 15 : Cessna 172 Y. Delpech L. Tipton 25 I 26 Y Conditions fair to poor but better than Nov-97 8:38 15: Cessna 172 Y. Delpech 1. Brenock Y New pilot & 2nd observer, clouds, fair/poor conditions. 17-Dec-97 8:41 15 : Cessna 172 Y. Delpech 1. Brenock II 0 II Y Good conditions; no 2nd observ.er in afternoon 23-Dec-97 9:05 13: Cessna 172 Y. Delpech none Y Good conditions, am. Aborted, pm: overcast. Resume 12/ Dec-97 8:59 12: Cessna 172 Y. Delpech A. Sellas Continuation of 12/23 flight. Fair to good conditions. 6-Jan-98 10:35 16: Cessna 172 Y. Delpech A. Sellas Y Good conditions, am. Aborted, pm : overcast. 13-Jan-98 9:04 10: Cessna 172 Y. Delpech none Continuation of 1/6 flight. Fair to good conditions. 30-Jan-98 9:22 16 : Lake Amphibian Y. Delpech A. Sellas 0 I Y Synoptic survey, poor pilot, fair survey. 0\ 19-Feb-98 9: 14 14: Cessna 172 Y. Delpech A. Sellas Y Good conditions overall. 24- Feb-98 9:25 14: Cessna 172 Y. Delpech A. Sellas Y Windy but clear; fair-good conditions. 4-M ar-98 9: 15 16: Cessna 172 Y. Delpech 1. Koel sch Y Good conditions overall. 28-Mar-98 9:28 12 : Cessna 172 Y. Delpech none Y Good conditions; flight aborted - airshow in area. 31-Mar-98 9:46 II : Cessna 172 Y. Delpech G. Guilbert - Continuation of 03/28 flight; flight aborted - strong wind. 2-Apr-98 II :53 13 : Cessna 172 Y. Delpech A. Sellas - Continuation of 03/28 fl ight. Good to fair conditions. 14-Apr-98 9:28 16: Cessna 172 Y. Delpech M. Koopman Y Good condition overall 28-Apr-98 9: 18 16: Cessna 172 Y. Delpech M. Koopman Y Excellent conditions in morning; overcast afternoon. 12-May-98 9:36 14: Cessna 172 Y. Delpech G. Guilbert FI ight aborted - air sickness; redo survey, see 19 May. 19-May-98 10:2 1 16: Cessna 172 Y. Delpech C. Hudak 84 I 85 Y Good conditions overall.. 2-Jun-98 9: 14 16: Cessna 172 Y. Delpech C. Hudak Y Good conditions overall. 10-Jun-98 9:2 1 16: Cessna 172 Y. Delpech C. Hudak Y Good conditions overall. 22-Jun-98 9:10 15: Cessna 172 Y. Delpech none Y Excellent conditions. 2-Jul-98 9: : Cessna [72 Y. Delpech C. Hudak [ 159 Y Good conditions overall. 23-Jul-98 8:41 14: Cessna 172 Y. Delpech C. Hudak Y Excellent conditions. 6-Aug-98 9:0t 10: Cessna 172 Y. Delpech C. Hudak Y Deteriorating conditions and storms; flight aborted. 7-Aug-98 8:39 II : Cessna 172 Y. Delpech C. Hudak Continuation of 8/06 flight. Good conditions overall. 20-Aug-98 9:03 II : Cessna 172 Y. Delpech C. Hudak Y Deteriorating conditions and storms; flight aborted. 24-Aug-98 9:09 14: Cessna 172 Y. Delpech C. Hudak - Continuation of 8/20 flight. Good conditions overall.

7 Myakka River Charlotte Harbor Gulfof Mexico,,. <;I. v,.' f 10 o Kiiometers Figure 1. Flight path of Charlotte County manatee aerial surveys, September August

8 250,--.t 200 ;: 'ri( '"..:' '.:,::: 00.. = = 0 U.. = Ii'.:. ",..:" I'"' Ill, [ii, o D, I,,, 0,, Iii, _,.. m I::':.... " "': q /: ::1 > ":' I"..:::... r.;il ::,: ': n A L I 1 ::1 1"1 1::1 HI" :".:: \1 t:::.:::: :::1 1:- :'".,'. ".: : ::::.::: :: ". :' ', I 1."" "..::'.. 0, 0, I, I, I, I, II, I, II, II, II, II, II, II, II, n n 1.,jI I? <I \: 1 1<1 1>- :::, ", EI Calves Adults Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Month foigure 2. Numbers of manatees sighted per month in Charlotte Co unty during aerial surveys, September August 1998.

9 N A V Charlotte Harbor Manatee Sightings.to I - 2 individuals o 20 Kilometers Figure 3. Manatee sighting locations in Charlotte County during aerial surveys, September August

10 e z I I'll I I II, 'I 1'/1 I'll "" Group Sizes Figure 4. Manatee group sizes in Charlotte County during aerial surveys, September August 1998.

11 N A Charlotte Harbor Manatee Sightings o Summer " Fall * Winter Spring o o \. '.'i 10 o Kilometers Figure 5. Seasonal manatee sightings in Charlotte County during aerial surveys, September Augusst y 11 '..

12 ( ' D' Charlotte Harbor N A Manatee Sightings... 1 calf 2 calves I'll 3-4 calves 10 o Kilometers Figure 6. Manatee calf sightings in Charlotte County during aerial surveys, September A'rigust