IRVINE ET AI..: MOVEMENTS AND ACTIVITIES OF ATLANTIC BOTTLENOSE DOLPHIN 



not belonging to the study herd, occasionally 

 moved along the southern edge of Tampa Bay, but 

 rarely approached tagged bottlenose dolphins and 

 were never observed moving south in the ICW. 

 The only tagged bottlenose dolphins known to 

 have left the study area were two radio-tagged 

 animals that left briefly (one moved 15 km north, 

 the other 10 km south) on the first night after 

 tagging. Both returned within 10 h. 



The home range boundary cues used by the 

 animals are unknown. At Tampa Bay, bottlenose 

 dolphins might have used acoustic or visual cues 

 associated with the sharp dropoff at the edge 

 of Tampa Bay. Bottlenose dolphins may use land- 

 marks to limit movements in Golfo San Jose, 

 Argentina (Wiirsig and Wiirsig 1979), although 

 known individuals also disappeared from the 

 study area for 6 mo, were resighted 300 km away 

 and then were rediscovered back in the study area 

 9 mo later (Wiirsig and Wiirsig 1977). Long-range 

 movements by some group members but not 

 by others have not been reported elsewhere; how- 

 ever, most studies of bottlenose dolphin home 

 range have been conducted in restricted geo- 

 graphical areas with relatively few identifiable 

 animals. (see review by Norris and Dohl 1980a). 



Movements and Activities 



Movement patterns were similar throughout 

 the northern part of the study area. Slow moving 

 groups of up to six animals often spent several 

 hours over grass flats 1-3 m deep, particularly 

 west of the ICW north of Sarasota Pass and east 

 of the ICW in northern Sarasota Bay (Figure 

 2). These groups were usually dispersed and 

 dynamic; individuals often approached each other 

 only occasionally, but all usually moved in the 

 same general direction. The pace of individuals 

 quickened at irregular intervals when apparent 

 feeding occurred. Typically, a group of bottlenose 

 dolphins was found in one part of the study area 

 for several survey days, before it moved to another 

 area, but locations and intragroup associations 

 were generally not predictable. 



Group members often converged and used 

 channels to move between areas, usually at speeds 

 of 2-5 km/h, although occasionally small groups in 

 tight formation moved along the ICW at speeds 

 exceeding 5 km/h. North-south movements of 

 up to 30 km in a day have been observed but were 

 not typical. 



Bottlenose dolphin distribution, and perhaps 



abundance, differed seasonally within the home 

 range (Figure 6). In winter, bottlenose dolphins 

 were most abundant in passes and along the 

 gulf shore, whereas during the warmer months 

 relatively higher numbers were sighted in the 

 channels and bays inshore of the barrier islands. 

 These localized changes in bottlenose dolphin 

 distribution may reflect changes in the distribu- 

 tion of food resources, or possibly seasonal changes 

 in abundance of sharks (Wells et al. 1980). 



Unlike the habitat of pelagic cetaceans, 

 which theoretically does not restrict horizontal 

 and vertical movements, the shallowness of many 

 parts of our study area restricted vertical move- 

 ments and thereby dictated bottlenose dolphin 

 travel routes and influenced the structure of 

 swimming groups. Bottlenose dolphins were only 

 occasionally observed crossing areas <1 m deep. 

 Bottlenose dolphins have partly beached them- 

 selves in Georgia marshes while pursuing 

 fish (Hoese 1971), and other dolphins have been 

 observed feeding in estimated depths of <50 cm 

 (A. B. Irvine pers. obs.; J. S. Leatherwood^). 



The habitat used by the bottlenose dolphins 

 reported here appears most like that of the hump- 

 back dolphin, Sousa sp., observed from cliffs in 

 South Africa (Saayman et al. 1972; Tayler and 

 Saayman 1972; Saayman and Tayler 1973, 1979; 

 Saayman et al. 1973) and bottlenose dolphins 

 observed in a bay in Argentina (Wiirsig and 

 Wiirsig 1977, 1979; Wiirsig 1978). In these areas, 

 the animals also usually moved in small groups 

 and fed individually. Although most bottlenose 

 dolphin sightings in our study area were east of 

 the barrier islands, tagged animals were also 

 periodically observed near shore in the Gulf of 

 Mexico. Bottlenose dolphins are found from well 

 offshore into extreme shallows in the Gulf of 

 Mexico (Leatherwood 1975; Leatherwood et al. 

 1978; Odell and Reynolds^")— suggesting a dis- 

 tribution that is similar to that of bottlenose 

 dolphins studied in South Africa (Saayman et al. 

 1972; Tayler and Saayman 1972; Saayman and 

 Tayler 1973, 1979; Saayman et al. 1973). 



Movements of bottlenose dolphins with the tides 

 were suggested by Ti-ue (1885), Gunter (1942), 

 Irvine and Wells (1972), Wiirsig and Wiirsig 



"S. Leatherwood, research biologist, Hubbs-Sea World 

 Research Institute, San Diego, CA 92109, pers. commun. 

 March 1980. , . 



"'Odell, D. K., and J. E. RevTiolds. 1980, III, Distribution 

 and abundance of the bottlenose dolphin. Tursiops truncatus, on 

 the west coast of Florida. Avail. Natl. Tech. Inf. Serv., Spring- 

 field, Va., as PB 80-197 650, 47 p. 



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