FISHERY BULLETIN VOL 77. NO 1 



FU'.LRK I. — Female blue shark near the ocean surface. 



FKiL'RE 2.— Study area at Catalina Island, Calif. Hatching indi- 

 cates sampling regions. Sharks feeding among squid schools 

 were observed at x . 



giant kelp, Macrocystis pynfera, composed the 

 major habitat alongthe island shore. A submarine 

 shelf, averaging 150 m deep, extends approxi- 

 mately 2 km seaward then slopes to depths near 

 900 m and forms the floor of the San Pedro Basin. 

 "Inshore" sampling stations were located above 

 the shelf within 3 km of the island, and "offshore" 

 stations centered approximately 6 km north of the 

 Isthmus, over deeper basin waters. 



Sharks were collected monthly between March 

 1975 and March 1976. Samples were taken during 

 morning and afternoon hours at both inshore and 

 offshore areas with an attempt to maintain a con- 

 sistent area-time sampling schedule. Sharks were 

 attracted to a drifting 7-m work boat by baiting 

 with slashed Pacific mackere\,Sc(>')ihcr japonicus, 

 suspended in a wire basket 5 m beneath the sur- 



face. Once attracted, sharks were captured by 

 hook and hand line using mackerel or market 

 squid, Lolign npalesvens, as bait. Sharks were 

 landed as quickly as possible to minimize regurgi- 

 tation and then measured, sexed, and inspected for 

 mating scars and general health. Contents of 

 esophagi and stomachs were filtered through 

 1-mm mesh netting and preserved. Recognizable 

 prey items and their digestive states were re- 

 corded on site. Intestinal tracts were occasionally 

 examined but contributed little information on 

 the diet because of the small pylorus which re- 

 stricted passage of identifiable prey fragments. 



Except for the market squid, cephalopods in the 

 diet were represented exclusively by beaks. Beaks 

 were paired into sets of upper and lower halves, 

 and identified when possible according to Clarke 

 (19621 andPinkasetal. (1971 1. Specific identifica- 

 tions were verified by comparisons with beaks 

 from collections of local species. Whole volumes of 

 squid were estimated from beak-size/body-weight 

 regressions for the major cephalopod families 

 given by Clarke ( 1962). For calculations, the den- 

 sity of cephalopod flesh was assumed to be 1 g/cm^. 

 A regre.ssion foi- the family Ocythoidae ( not given by 

 Clarke) was generated by plotting beak measure- 

 ments and body weights from local specimens on 

 Clarke's Octopodidae and Argonautidae regres- 

 sions and constructing a parallel relationship 

 curve. Beak-size/body-weight regressions for 

 Vampyroteuthis infernalis were obtained from 

 specimens of local collections. Unidentified 

 cephalopods were omitted from the quantification 

 as they represented only a minor portion of the 

 diet (four small, infrequent species in eight 

 stomachs). 



In order to approximate normal shark feeding 

 times, digestive rates for captive sharks were de- 

 termined and then compared with field data on the 



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