FISHERY BULLETIN; VOL. 77. NO. 4 



pull out the harpoon and swim away (W. A. 

 Walker''). 



14. (UnpubHshed). On 20 May 1973, an im- 

 mature female was found stranded on southeast 

 Farallon Island, off San Francisco, Calif (approx- 

 imately lat. 37°42' N, long. 123"00' W). The avail- 

 able measurements for the specimen are as fol- 

 lows: total length 270 cm, dorsal fin 27.5 cm, 

 axilla-tip of flipper 5 cm, origin of flipper to tip of 

 lower jaw 46.5 cm, anus-tip of lower jaw 178 cm, 

 width of flukes 62 cm. The specimen was not col- 

 lected (R. L. Brownell, Jr. see footnote 10). 



15. (Published). On 18-19 June 1973, four 

 females and a fifth animal of undetermined sex, all 

 about 13 ft long (400 cm) and weighing 500-600 lb 

 (73-77 kg) stranded alive at Punta Buffeo, Baja 

 California, about 100 mi (160 km) south of San 

 Felipe on the northwest coast of the Gulf of 

 California (approximately lat. 29°55'20" N, long 

 114"'26'20"W). All five animals were towed out to 

 sea (dead), and no materials were retrieved 

 (Leatherwood et al. 1979). 



16. (Unpublished). On 8 December 1974, a 

 female stranded alive at the Manhattan Beach 

 Pier, Los Angeles, Calif, (approximately lat. 

 33°55' N, long. 118°25' W). The animal was alive 

 when it was collected by Marineland of the Pacific 

 but died almost immediately after collection. It 

 was photographed, measured, and necropsied at 

 the Los Angeles County Museum of Natural His- 

 tory, where it is currently held as specimen LACM 

 47145. Detailed findings will be reported 

 elsewhere (W. F. Samaras and D. R. Patten ). 



17. (Unpublished). On 10 March 1975, a 348 

 cm female stranded alive at Port Discovery, 

 Wash., in the Strait of Juan de Fuca (about lat. 

 48'02' N, long. 122°52' W), perhaps driven ashore 

 by killer whales. The animal was recovered alive 

 and taken to Seattle Marine Aquarium where it 

 died on 11 March. The complete skeleton is in the 

 collection of the NWAFC (No. 1975-1). 



At-Sea Sightings 



We found 16 previously published records of 

 at-sea sightings of Risso's dolphins for the study 

 area (Table 1) and 194 additional previously un- 



published reliable records (see footnote 8) (Figure 

 5). When examined by latitude (Figure 5), the 

 distribution of sightings falls into three major 

 groups — those from the Equator to approximately 

 lat 20° N (Zone I); those thence north to approxi- 

 mately lat. 43" N (Zone II); and those north of lat. 

 43° N (Zone III). Zones I and II are separated by a 

 broad region characterized by very few sightings, 

 centering at about lat. 20° N and extending from 

 lat. 14° to 29° N. All except two sightings in that 

 area of low density were within 60 mi of the Mexi- 

 can coast, though seaward of the continental shelf. 

 The separation between Zones II and III is less 

 pronounced, centering at lat. 43° N emd extending 

 from lat. 38° to 45° N. 



Regarding seasonality, records in Zone I are al- 

 most exclusively limited to first and second quar- 

 ters, and the majority of those from Zone III are 

 from the period July through October. Both of 

 these apparent seasonal fluctuations result from 

 the biases in observation effort discussed above. 

 Those from Zone II are distributed throughout the 

 year. Records from north of Point Conception (lat. 

 35° N) are most numerous in the third quarter 

 (Figure 6). 



Off southern California (approximately lat. 

 31°-35° N), records from 1959 to 1975 were 

 sporadic, reaching a peak of 11 in 1974 (Table 3). 

 Until 1971 the majority of sightings for the area 

 were seaward of the 100-fathom curve; however, 

 beginning in 1971 and increasing in frequency 

 through 1974 (9 of 11) and 1975 (3 of 3), most 

 sightings were over the continental shelf 



Although surface water temperatures were not 

 reported for most sightings, Risso's dolphins have 

 been sighted in waters ranging from 28° to 10° C. 

 Sightings in Zone I cover the full range of temper- 

 atures reported for the area. Sightings off south- 

 ern California in 1974 and 1975 were associated 

 with water temperatures above 19° C. Of the 22 



Table 3. — Summary of sightings of Risso's dolphins off southern 

 California labout lat. 3r-36° Nl. 1959-75, showing the frequency 

 of encounter over and seaward of the continental shelf. 



"W. A. Walker, 21 Barkentine Road. Rancho Palos Verdes, 

 CA 93704, pers. commun. to Leatherwood 1975. 



"W. F. Samaras. Research Associate, and D. R. Patten, 

 Curator, Department of Mammals. Los Angeles County Museum 

 of Natural History, Los Angeles, CA 90007, pers. commun. to 

 Leatherwood 1975. 



958 



