Movements of Pelagic Dolphins (Stenella Spp.) in the 



Eastern Tropical Pacific as Indicated by Results of 

 Tagging, With Summary of Tagging Operations, 1969-76 



W. F. PERRIN 1 , W. E. EVANS 2 , and D. B. HOLTS 1 

 ABSTRACT 



Through 1976, 3,712 small cetaceans were tagged in the course of research cruises operating out of 

 the Southwest Fisheries Center. These included 2,996 spotted dolphins, Stenella attenuata; 324 spin- 

 ner dolphins, S. longirostis; 193 common dolphins, Delphinus delphis; and 113 bottlenose dolphins, 

 Tursiops truncatus. Others tagged in small numbers included Pacific whitesided dolphins, Lagenor- 

 hynchus obliquidens; striped dolphins, Stenella coeruleoalba; and a short-finned pilot whale, Globice- 

 phala macrorhynchus. Several types of tags were used. Tags have been recovered from 97 spotted dol- 

 phins and 7 spinner dolphins. Time at liberty ranged from less than 2 h to more than 4 yr. Net distance 

 traveled ranged from 7 to 582 n.mi. Average short-term movement in the spotted dolphin is 30-50 

 n.mi./day; range is 200-300 n.mi. in diameter, and seasonal onshore-offshore migrations may exist. 



INTRODUCTION 



Populations of pelagic dolphins are important to the 

 purse seine fishery for yellowfin tuna in the eastern 

 tropical Pacific and are affected by the fishery. 3 Ade- 

 quate assessment of the impacts of the fishery on the dol- 

 phin populations requires knowledge of such aspects of 

 life history as home range and seasonal migration. For 

 this reason, we began a program of tagging dolphins in 

 1969. The tagging program was specifically designed to 

 examine movements, but the tagging itself was largely 

 opportunistic. In addition, research projects with other 

 objectives but involving tagging have also yielded infor- 

 mation on movements. The main purpose of this report is 

 to summarize and to report the results of analyses of data 

 on movements of spotted dolphins, Stenella attenuata, 

 and spinner dolphins, S. longirostris, yielded by tag 

 returns through 1976. A secondary purpose is to summa- 

 rize and document all dolphin tagging operations carried 

 out in conjunction with dolphin/tuna research at the 

 Southwest Fisheries Center, La Jolla, Calif., from 1969 

 through 1976. This is necessary because of the possi- 

 bility that tagged dolphins released by us may be re- 

 covered by other investigators not familiar with our pro- 

 gram. We suspended field work in our tagging program in 

 1976, pending development of better tags and design of a 

 plan for large-scale tagging aimed at estimating popula- 

 tion sizes. The results of the expanded program will be 

 the subject of future reports. 



■Southwest Fisheries Center, National Marine Fisheries Service, 

 NOAA, La Jolla, CA 92038. 



2 Hubbs-Sea World Research Institute, Sea World, San Diego, CA 

 92109. 



-Report of the Workshop on Stock Assessment of Porpoises Involved in 

 the Eastern Pacific Yellowfin Tuna Fishery. Unpubl. Manuscr., 109 

 p. SWFC Admin. Rep. No. LJ-76-29, Nat. Mar. Fish. Serv., La Jolla, 

 CA 92038. 



Many small marine odontocetes are thought to under- 

 go migrations of varying scale in time and distance. Most 

 published conclusions about movements have been 

 based on sightings or strandings and have to do with 

 season of the year or sea surface temperature. Fraser 

 (1934) noted a possible intrusion of elements of the 

 warm -temperate Atlantic cetacean fauna (including Del- 

 phinus delphis) into the North Sea during a year of 

 anomalous sea-surface warming. Sightings and corre- 

 lated oceanographic data suggest that the distributions 

 of dolphins (Lissodelphis peroni, Lagenorhynchus cru- 

 ciger, Lagenorhynchus obscurus, and Delphinus del- 

 phis) off the east coast of New Zealand are "closely asso- 

 ciated with certain temperature ranges and conse- 

 quently with specific water masses and convergence 

 regions," causing different animals to be seen in summer 

 than in winter (Gaskin 1968). Similarly, Kasuya (1971) 

 found, on the basis of aerial sightings, that warm-water 

 delphinids, including Stenella attenuata, in Japanese 

 waters migrate north in the summer season as far as Hok- 

 kaido; whereas cold-water forms, such as Phocoenoides 

 dalli and Lissodelphis borealis, migrate south in the 

 winter. The northern extent of the distribution of the 

 warm-water forms may vary seasonally as much as 13° of 

 latitude (780 n. mi.) (Miyazaki et al. 1974). Evans (1975) 

 demonstrated the existence of similar seasonal migra- 

 tions by the common dolphin, D. delphis, off the coasts 

 of southern California and Baja California. Several other 

 similar studies have been carried out, and this review is 

 not exhaustive. 



Very little information has been available on home 

 range of pelagic dolphins. As Norris (1967) noted, some 

 dolphins seem quite sedentary. He found that herds of 

 spinner dolphins, Stenella longirostris, are consistently 

 found off limited stretches of coast; five such home 

 ranges have been tentatively recognized off Oahu, 

 Hawaii. On the other hand, some other dolphins are very 



