BEHAVIOR AND ECOLOGY OF THE DUSKY DOLPHIN, 

 LAGENORHYNCHUS OBSCURUS, IN THE SOUTH ATLANTIC 



Bernd Wursig and Melany Wursig' 



ABSTRACT 



Dusky dolphins were present in Golfo San Jose. Chubut, Argentina, during most of the year, with a 

 seasonal low in abundance during winter and a high in summer. The presence of the prey species 

 southern anchovy, £ngrau/is anchoita. appeared to affect seasonal movements. 



Surface feeding was highly visible and birds also fed on fish schools which dolphins herded to the 

 water surface. Surface feeding occurred mainly in spring and summer in the study area, and in late 

 summer and fall m more oceanic waters near the mouth of the bay. This surface feeding pattern 

 corresponded with the presence of southern anchovy. " 



Dolphins moved in small groups of about 15 individuals while resting in early morning and while 

 looking for food in late morning. Group sizes increased during surface feeding as groups joined existing 

 feeding activity . Because surface feeding occurred mainly around noon and early afternoon, group sizes 

 increased at those times. Dives were longer before and during feeding, and shorter while resting. 

 During spring, summer, and fall nights, dives were shorter, leading to the possibility that dolphins 

 were resting at those times The nonsurface feeding period corresponded with nighttime dispersal of 

 southern anchovy schools. Dolphins moved in shallow water while resting and in deeper water while 

 surface feeding. Near shore resting may be a predator-avoidance mechanism. 



Most aerial behavior occurred during surface feeding, with behavior before and during surface 

 feeding related to either herding and confining prey or possible communication of neighboring groups. 

 Postfeeding aerial displays were assumed to serve a social function. 



Calves were bom mainly in the summer. 



Recently there has been an increase in the number 

 of studies of movements and migration patterns, 

 behavior, and ecology of dolphins. Most of this 

 work has consisted of long-term observations of 

 the bottlenose dolphin, Tursiops sp. (Caldwell et 

 al. 1965; Caldwell and Caldwell 1972; Tayler and 

 Saayman 1972; Irvine and Wells 1972; Saayman 

 et al. 1972, 1973; Saayman and Tayler 1973; 

 Leatherwood 1975; Odell 1975, 1976; Castelloand 

 Pinedo 1977; Shane 1977; Wursig and Wursig 

 1977, 1979; Wursig 1978; Wells et al. in press; 

 Irvine et al.^), but other odontocete cetaceans have 

 received attention as well (review to 1974 by Nor- 

 ris and Dohl in press; Saayman and Tayler 1979, 

 on Sousa sp.; Evans 1976, on Delphinus delphis, 

 Norris and Dohl 1980, on Stenella longirostris; 

 Gaskinetal. 1915, on Phocoena phocoena.'Wursig 

 in press, on Lagenorhynchus obscunis ). This paper 



'State University of New York at Stony Brook, Program for 

 Neurobiology and Behavior; present address: Center for Coastal 

 Marine Studies, University of California, Santa Cruz, CA 95064. 



^Irvine, A. B, M. D. Scott, R. S. Wells, J. H. Kaufmann, and W. 

 E. Evans. 1979. A study of the movements and activities of 

 the Atlantic bottlenose dolphin, Tursiops truncatus, including 

 an evaluation of tagging techniques. Final report for US 

 Marine Mammal Commission. Contracts MM4AC004 and 

 MM5AC0018, 53 p. 



Manuscript accepted July 1979 



FISHERY BULLETIN: VOL. 77, NO, 4. 1980. 



presents data on the yearly and daily occurrence 

 and feeding cycles, movement patterns, general 

 and social behavior, and ecology of the dusky dol- 

 phin, Lagenor/jy'Jc/iz^s obscurus, in a south Atlan- 

 tic bay on the coast of Argentina. 



Little information on dusky dolphins is avail- 

 able in the published literature. Gaskin (1968) 

 described the distribution of these animals around 

 New Zealand relative to sea-surface temperature, 

 and Gaskin (1972) presented a summary of the 

 literature. Although the genus Lagenorhynchus 

 appears worldwide, populations ofL. obscurus are 

 confined to the Southern Hemisphere, most nota- 

 bly around New Zealand, South Africa, and South 

 America. The exact northern and southern limits 

 of the species are not known. Brownell (19651 

 states that dusky dolphins are distributed circum- 

 polar to lat. 30' S, but this is disputed by Gaskin 

 (1972). According to Rice (1977), L. fitzroyi is 

 synonymous with L. obscurus. 



More information is available on the Pacific 

 whitesided dolphin, L. obliquidens. It has been 

 described by Brown and Norris (1956), Norris and 

 Prescott ( 1961), and others. A recent review of the 

 status of this species in the eastern North Pacific 



871 -S^C 



