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



captured and sexed several times, error in sex 

 determination is not likely. She was occasionally 

 seen with the same group of subadult males 

 that had been observed engaging in homosexual 

 activities, and on one occasion she appeared to 

 engage in sexual activities with at least one 

 member of that group. 



The associations of longest duration involved 

 cows and calves, although relatively prolonged 

 aggregations of subadult males and frequent asso- 

 ciations of adult males with adult females 

 were noted in the spring. One calf was observed 

 during 30 of 32 sightings of the apparent mother 

 over a period of 15 mo, and another calf was 

 observed with its mother on all of 20 sightings 

 during a 9-mo period. We did not observe straying 

 of calves, as has been noted in captivity (see 

 review by M. C. Caldwell and D. K. Caldwell 1972) 

 and inferred for free-ranging bottlenose dolphins 

 in Argentina (Wiirsig 1978) and the Gulf of 

 Mexico (Leatherwood^^). 



When pursued during capture attempts, calves 

 stayed close beside their fleeing mothers, appar- 

 ently being partly pulled along in the suction 

 created by the mother's movement through the 

 water (Norris and Prescott 1961; Norris and 

 Dohl 1980a; Leatherwood footnote 12). While the 

 mother was being tagged, calves remained close to 

 the stretcher, often emitting underwater whistles 

 audible in air. A calf released outside the net 

 quickly became tangled in the net while attempt- 

 ing to return inside, where its mother was 

 trapped. When a cow was released before her calf 

 was freed, she invariably patroled outside the net 

 until the calf was released. On one occasion a 

 loud whistle from a bottlenose dolphin calf being 

 tagged brought the mother rapidly to within 5 m of 

 the capture net from a point about 75 m away. 

 Apparently similar behaviors have been observed 

 for Stenella sp. involved in the purse seine fishery 

 for yellowfin tuna, Thunnus albacares (W. F. 

 Perrin^^). Close approaches by large male killer 

 whales, Orcinus orca, to the outside of an enclo- 

 sure containing a killer whale calf have also been 

 observed by A. B. Irvine in Puget Sound. 



'^Leatherwood, S. 1977. Some preliminary impressions on 

 the numbers and social behavior of free swimming bottlenosed 

 dolphin calves ^Tursiops truncatus^ in the northern Gulf of 

 Mexico. In S. H. Ridgway and K. W. Benirschke i editors), 

 Breeding dolphins, present status, suggestions for the future, p. 

 143-167. Avail. Natl. Tech. Inf. Serv, Springfield, Va., as 

 PB-27:3 673. 



'■'W. F. Perrin, fi.shery biologist. Southwest Fisheries Center 

 La Jolla Laboratorv, National Marine Fisheries Service, NOAA, 

 La Jolla, CA 92037, pers. commun. March 1980. 



Dolphins being pursued by the capture boat fled 

 as a close-knit group often in a line abreast 

 formation. As with bottlenose dolphins off Cali- 

 fornia (Norris and Prescott 1961; Norris and 

 Dohl 1980a) and off Louisiana (Leatherwood and 

 Platter'"*), some bottlenose dolphins recognized 

 the capture boat and began fleeing rapidly 400 m 

 or more ahead of the boat. The bottlenose dolphins 

 apparently associated the sound of the boat's 

 engine with past captures, since naturally marked 

 animals not previously subjected to our capture 

 attempts did not flee. When part of a bottlenose 

 dolphin group was encircled, the remaining mem- 

 bers did not temporarily remain nearby, as has 

 been reported for Steno hredanensis (Evans 1967), 

 common dolphins (Pilleri and Knuckey 1968), 

 the dusky dolphin, Lagenorhynchus obscurus 

 (Wiirsig and Wiirsig 1980), and killer whales 

 (Balcomb and Goebel footnote 6). We often ob- 

 served and sometimes recaptured dolphins near 

 earlier capture sites, suggesting that capture 

 areas were not avoided. 



Behaviors associated with the formation and 

 maintenance of intragroup associations are not 

 well understood. Studies of captive animals have 

 indicated that dominance, exerted by combina- 

 tions of physical posturing, aggression, and vocal- 

 ization, may be important in the establishment 

 and maintenance of social hierarchies (Tavolga 

 1966; M. C. Caldwell and D. K. Caldwell 1967, 

 1972; Evans and Bastian 1969). Most studies of 

 captive dolphins, however, have been of <15 

 dolphins, often interspecifically mixed, and con- 

 fined in a tank. The dominance hierarchies and 

 social structure described for captive groups may 

 therefore not represent the social organization of 

 free-ranging bottlenose dolphins. For instance, 

 the concept of microterritories suggested for cap- 

 tives (M. C. Caldwell and D. K. Caldwell 1972; 

 Tayler and Saayman 1972) and presumably main- 

 tained by dominance relationships is probably not 

 relevant to the study of wild bottlenose dolphins, 

 which move constantly and change companions 

 often. The small "family unit" concept proposed by 

 McBride and Kritzler (19511 is also not compatible 

 with our observations of dynamic group member- 

 ship. Evans and Bastian (1969) proposed that the 

 spatial consideration of primary importance to 



'■' Leatherwood, S., and M, F Platter 1975. Aerial assess- 

 ment of bottlenosed dolphins off Alabama. Mississippi, and 

 Louisiana. In D. K. Odell, D. B. Siniff, and G. H. Waring 

 leditorsi, Tursiops truncatus Assessment Workshop, p. 49-86. 

 Avail. Natl. Tech. Inf Serv.. Springfield, Va., as PD-291-161. 



683 



