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



were sometimes briefly observed in the bottlenose 

 dolphin's mouth at the end of the chase. Similar 

 behavior by feeding bottlenose dolphins has 

 been described by Leather wood (1975), Shane and 

 Schmidly (footnote 5), and Shane (1980). The 

 upside down feeding behavior reported for bottle- 

 nose dolphins (Leatherwood 1975) and humpback 

 dolphins (Saayman and Tayler 1979) was occa- 

 sionally observed. Obvious herding offish as has 

 been reported for several small cetaceans in near- 

 shore areas (D. K. Caldwell and M. C. Caldwell 

 1972; Saayman et al. 1972; Tayler and Saayman 

 1972; Saayman et al. 1973; Leatherwood 1975; 

 Saayman and Tayler 1979; Shane and Schmidly 

 footnote 5) was not observed. 



In the Gulf of Mexico (at depths of 3-6 m), rapid 

 convergence by bottlenose dolphins within a 

 radius of about 200 m was observed on several 

 occasions. The bottlenose dolphins dove and re- 

 mained submerged for 30-90 s in an area where no 

 fish were obvious. Then a number of bottlenose 

 dolphins surfaced almost simultaneously in a 

 confined area amid large numbers of jumping 

 striped mullet, some of which were captured in 

 midair. Although cooperative feeding cannot 

 be confirmed, at the very least the bottlenose 

 dolphins were feeding on the same school offish, 

 and we suspect they may have herded the school at 

 the surface in an organized way. This behavior 

 differs somewhat from other accounts of coopera- 

 tive feeding (see review by Norris and Dohl 1980a) 

 because the fish school remained at the surface 

 only briefly, after which the bottlenose dolphins 

 milled in the area for 1-3 min before gradually 

 dispersing into small groups. On one occasion, a 

 sequence of rapid convergence on a concentrated 

 fish school, brief intense feedings, and then dis- 

 persal into small groups was repeated three times 

 within 45 min by 20-30 bottlenose dolphins. 



Concentrated feeding at more productive areas 

 may optimize food availability for flocking birds in 

 the Mojave Desert (Cody 1971), and a similar 

 strategy has been suggested for common dolphins 

 (Evans 1971, 1974, 1975) and spinner dolphins 

 (Norris and Dohl 1980a). These pelagic cetaceans 

 may feed intensively, primarily after dusk and 

 before dawn, in productive areas of the deep 

 scattering layer before moving on. Theoretically, 

 if the dolphins do not return to the same site for 

 some time, the food source will replenish. In 

 contrast, bottlenose dolphins in our study area 

 may exert an almost constant pressure on avail- 

 able food resources. Inshore regions of the study 



area and the waters along the Gulf beaches were 

 often traversed several times in a single day by 

 different groups of foraging bottlenose dolphins. 

 Evidence from captives and anecdotal accounts 

 from commercial fishermen indicate that bottle- 

 nose dolphins also feed at night. Bottlenose dol- 

 phins may feed on different ecotypes in different 

 geographic areas (Walker'-^), and presumably T. 

 truncatus in coastal Florida have prey and feeding 

 strategies different from bottlenose dolphins in 

 pelagic habitats. Habitat differences are therefore 

 important to any generalized concept of cetacean 

 behavior and herd function. Because ecological 

 variables influence social behavior and therefore 

 the structure of small-cetacean herds (see reviews 

 by Norris and Dohl 1980a; Wells et al. 

 1980), studies of adjacent inshore and offshore 

 populations of bottlenose dolphins could do 

 much to elucidate the influence of habitat on 

 cetacean behavior. 



Reproduction and Growth 



Calves were defined as noticeably smaller 

 bottlenose dolphins closely associating with a 

 single larger animal and composed 8.27c of the 

 bottlenose dolphins sighted. Extensive observa- 

 tions of tagged cow-calf pairs suggest that the 

 above definition was generally applicable. Ten 

 calves iX = 171 cm; SE = 9) represented 197c of all 

 captures and recaptures. The relative number of 

 calf sightings per month varied significantly 

 (P<0.0005; chi-square contingency tables) from 

 August 1975 to July 1976. It is not clear from the 

 sighting data if the calves were produced during a 

 bimodal breeding season with peaks in late spring 

 and early fall, as suggested by Harrison and 

 Ridgway (1971), or during a continuous breeding 

 season with increases in activity during spring 

 and fall. Many small cetaceans copulate through- 

 out the year, and evidence for discrete breeding 

 seasons is still contradictory (see review by Saay- 

 man and Tayler 1979). 



Grovvi;h measurements were obtained from the 

 repeated captures of calves and the recapture of 

 a young individual originally captured in 1970 

 (Irvine and Wells 1972). Two calves were captured 

 several times during the study; one grew from 172 

 to 183 cm in 13 mo, and the other from 189 to 198 



'^Walker, W. A. 1981. Geographical variation in mor- 

 phology and biology of bottlenose dolphins iTursiops> in the 

 eastern North Pacific. Natl. Mar. Fish. Serv. Admin. Rep. LJ 

 81 03C. Unpubl. rep. 



685 



