nSHERY BULLETIN: VOL 77. NO, 1 



advantage of the survey to count manatees and to 

 note numbers of manatee calves. 



MATERIALS AND METHODS 



The survey design follows the recommendations 

 of Leatherwood et al. ( 1978) for a strip census of 

 bottlenosed dolphins. Thirty-nine east-west 

 transects were placed 4.63 km (2.5 n.mi.) apart. 

 Each day for six successive days (10-15 AugustI 

 the replicate transects were flown in a Cessna 172 

 Skyhawk'5 travelling 167.0 km/h (90 kn) at an 

 altitude of 150 m (500 ft). 



The visual angle which provided 0.463 km (0.25 

 n.mi. ) coverage on each side was determined prior 

 to the survey and marked by tape on the wing 

 struts and windows. One observer on each side 

 searched for dolphins within 0.463 km of the air- 

 craft. Sightings near the outer boundary of the 

 survey strip were checked using an inclinometer. 

 Sightings outside the survey strip and on connect- 

 ing legs were ignored. Each time dolphins were 

 sighted within the survey strip, the aircraft di- 

 verted to the group and circled until the following 

 information could be obtained: location of the 

 sighting (using landmarks and local navigational 

 aids), number of individuals, number of apparent 

 calves of the year, group activity, and swimming 

 direction. 



Each time manatees were sighted, both on the 

 survey transects and on the legs connecting tran- 

 sects, the same procedure was followed. Adults 

 and calves were clearly distinguishable (calves 

 were defined as small animals in the close com- 

 pany of a much larger adult). A total of five indi- 

 viduals of a third class, intermediate-sized ani- 

 mals, were logged separately as possible older 

 calves. Because manatees were secondary targets 

 of the survey, less time was generally spent on 

 manatee than on dolphin sightings. 



As an index to through-water visibility, records 

 were maintained on 3 days of the percentage of 

 each transectfor which the bottom within the strip 

 was visible from the aircraft. To minimize effects 

 of other potential variables on counts the follow- 

 ing controls were exercised: all flights were con- 

 ducted between 0725 and 1300; observers 

 remained the same and maintained the same posi- 

 tions in the aircraft; altitude and speed were held 

 constant; methods of searching and circling were 



the same throughout; estimates of totals and 

 numbers of calves were agreed upon by observers 

 before each sighting was logged and transects re- 

 sumed. Surveys were only conducted when the sea 

 surface and winds were estimated to be a Beaufort 

 number of 1.5 or below. Because weather was gen- 

 erally excellent for all 6 days, this required only 

 one 40-min suspension on 14 August to permit a 

 rain squall and associated winds to pass. Each day, 

 during the hours of the aerial surveys, observers 

 stationed on shore logged numbers of dolphins and 

 manatees entering or leaving Indian River by 

 Sebastian and Fort Pierce Inlets and the direction 

 of travel of these animals relative to tidal flow. 



Resultant data on dolphins were analyzed fol- 

 lowing the procedures outlined by Leatherwood et 

 al. (1978) for a strip census of bottlenosed dol- 

 phins. Inherent in the application of this method is 

 the critical assumption that all dolphin herds 

 within the 0.926 km (0.5 n.mi.) are observed. Re- 

 sultant data on manatees are presented as inci- 

 dental observations with no attempt to estimate 

 population size. 



RESULTS 



Dolphins 



On each replicate of the transects, I surveyed 

 approximately 174.0 linear km (94 n.mi.) or 161.2 

 km^ (47 n.mi. 2) of water, an estimated 20^ of the 

 surface area of the rivers. In all, 64 sightings of 

 dolphins, totaling 507 animals (Table 1) were 

 made on the transects (Figures 1, 2, 3). Sightings 

 included from 1 to 35 individuals about a mean of 

 8.2 and a median of 5. The distribution of herd 

 sizes by replicate is shown in Figure 4. 



Animals clearly identifiable as calves of the 

 year were seen with 22 groups (34.4%) and com- 

 prised 8.n of all animals seen (Table 1). Slightly 

 larger animals, perhaps older calves of the year. 



T.^BLE 1. — Numbers of herds and individuals of bottlenosed 

 dolphins observed in Indian and Banana Rivers, Fla.. during 

 aerial surveys, 10-15 August 1977. 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



48 



