DISTRIBUTION AND MOVEMENTS OF RISSO'S DOLPHIN, 

 GRAMPUS GRISEUS, IN THE EASTERN NORTH PACIFIC 



Stephen Leatherwood,' William F. Perrin,^ Vicky L. Kirby,^ Carl L. Hubbs/ and Marilyn Dahlheim* 



ABSTRACT 



Records of occurrence are summarized from 22 strandings/collections and 210 sighting records from 

 miscellaneous soxirces. When available, levels of effort have been identified and utilized to interpret the 

 trends in distribution and movement apparent from the data. Risso's dolphins occur from at least the 

 Equator (southern end of area examined) north to approximately latitude 50° N. with regions of 

 apparently very low density centering at about latitude 20' and 43° N. Records from northern and 

 inshore portions of the range were most numerous during late spring through early fall. Both within 

 and among years, periods of greatest abundance for the species north of latitude 43° N, near Monterey 

 Bay, California, and over the southern California continental borderland appear to correspond with 

 protracted periods of warm water Groups contained from 1 to an estimated 220 animals, about a 

 geometric mean of 10.7. An estimated 76.4% of the groups contained fewer than 20 animals. 



The Risso's dolphin or gray grampus, Grampus 

 griseus, is widely distributed in tropical and tem- 

 perate waters around the world. It occurs on the 

 western side of the Atlantic Ocean from at least 

 Newfoundland (approximately lat. 50° N, Leath- 

 erwood et al. 1976) south to Cape Horn (approxi- 

 mately lat. 53° S, Norris''), and in the Gulf of 

 Mexico (True 1885; Gunter 1954; Paul 1968) and 

 the Caribbean (Caldwell et al. 1971). On the east- 

 ern side of the Atlantic it occurs from the Shetland 

 Islands, Scotland (Turner 1892), south to the Cape 

 of Good Hope (approximately lat. 34° S, Barnhard 

 1954), including the North Sea (Schultz 1970), and 

 throughout the Mediterranean Sea complex (Baz- 

 zauti 1910; Tamino 1953; Pilleri and Gihr 1969), 

 including the Adriatic (Trois 1883; Ninni 1901; 

 Carrucio 1906; Riedl 1965; Pilleri and Gihr 1969). 

 It also occurs in the Red Sea (Hershkovitz 1966) 

 and in the Indian Ocean (Ellerman et al. 1953; 



'Biomedical Branch, Naval Ocean Systems Center, San Diego, 

 Calif.; present address: Hubbs/Sea World Research Institute, 

 1700 South Shores Road, San Diego, CA 92109. 



^Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 

 92038. 



^Department of Biology, San Diego State University, San 

 Diego, CA 92115. 



'Scripps Institution of Oceanography, La Jolla, CA 92037. 

 Deceased. 



'Department of Biology, San Diego State University; present 

 address: Northwest and Alaska Fisheries Center, National 

 Marine Fisheries Service, NOAA, 7600 Sand Point Way NE, 

 Seattle, WA 98115. 



«Norris, K. S. 1968. Cruise report of the R/V Hero. 

 November 12-December 11, Valparaiso-Puntarenas, Chile, 11 

 p. Coastal Marine Laboratory, University of California, Santa 

 Cruz, CA 95060. 



Weber 1923), at least to the Indo- Australian Ar- 

 chipelago, and on the west side of the Pacific Ocean 

 from the Commander Islands (approximately lat. 

 55° N, Sleptsov 1961) south to New Zealand (Hec- 

 tor 1873; Parker 1934; Alpers 1960; Gaskin 1968; 

 Baker 1974), including the South China Sea, the 

 Philippine Sea (Baker 1974), and the waters 

 around the New Hebrides (Maxwell 1952), the 

 Solomon Islands (Dawbin 1966), and New Guinea 

 (Gaskin 1972). On the eastern side of the Pacific it 

 has been reported from the Bering Sea (Clark 

 1945) and British Columbia (Guiguet and Pike 

 1965) south to Valparaiso, Chile (Aguayo 1975), 

 and Cape Horn (Norris see footnote 6), including 

 the Gulf of California (Leatherwood et al. 1979). 

 That Risso's dolphins are present in Hawaiian 

 waters as well is indicated by three sightings and a 

 stranding on Maui in 1977 (E. W. Shallenberger'). 

 Davies (1963) remarked on the species' overall 

 distribution that it is basically tropical but ex- 

 tends its ranges poleward to overlap the ranges of 

 temperate forms, though they generally do not 

 penetrate so far into high latitudes. In all areas, 

 the species' distribution is known only from in- 

 frequent stranding records and at-sea sightings, 

 and published accounts continue to restate those 

 records, often without adding substantial new 

 data. Details of the animal's distribution and 

 movements Eire not reported. This paper reviews 

 the information available through 1975 on Risso's 



Manuscript accepted May 1979 



FISHERY bulletin VOL 77. NO. 4. 1980 



'E. W. Shallenberger, Curator, Sea Life Park, Waimanalo, HI 

 96795, pers. commun. to Leatherwood September 1977. 



951 



