FISHERY BULLETIN: VOL 77, NO 1 



shark diets in other coastal areas of the world 

 (Bigelow and Schroeder 1948; LeBrasseur 1964; 

 Stevens 1973). Major concentrations of anchovies 

 in the California Current system were centered in 

 the semiprotected waters of the Southern Califor- 

 nia Bight (Mais 1974) which lies between Point 

 Conception and Point Descanso, Mexico (approx- 

 imately from lat. 32.0°N to 34.5°N, area of about 

 50,000 km^). The main portion of the southern 

 California anchovy population was reported by 

 Mais to be distributed within 37 km of the main- 

 land over deep water (228.6-731.5 ml which in- 

 cludes the study area at Catalina. 



The most prevalent schooling behavior for an- 

 chovies in deep open waters (bottom depth >183 

 m) was the formation of small (4-15 m thick), 

 near-surface daytime schools (0-54.9 m deep) that 

 dispersed at night into a thin surface scattering 

 layer (Mais 1974 1. Field observations from the 

 present study indicate a similar behavior for an- 

 chovies near Catalina. In offshore waters during 

 the day, anchovies occurred in large, dense, 

 polarized schools near the surface. In the early 

 evening, schools dispersed horizontally into less 

 dense feeding assemblages with individuals 

 spaced approximately 0.5 m apart. Later at night 

 (0100-0400 h) more dispersed groups and solitary 

 individuals were observed on several occasions, 

 indicating a more complete nocturnal dissolution. 



In spite of the abundance of this prey no sharks 

 examined near Catalina had stomachs distended 

 with anchovies; usually only one or two had been 

 taken per day. Data from the digestion studies 

 indicate that most predation on anchovies oc- 

 curred in predawn hours which correlates with the 

 increased nocturnal activity of telemetered sharks 

 reported by Sciarrotta and Nelson ( 1977). It seems 

 probable then, that the few anchovies taken by 

 each shark was at least partially due to the noc- 

 turnal dispersion of schools in offshore waters, 

 whereby assemblage densities were reduced and 

 anchovies taken individually. 



The localized variability of anchovy abundance 

 and schooling behavior that existed between areas 

 and seasons pre.sented different feeding oppor- 

 tunities for sharks. For example, blue sharks cap- 

 tured during the day off Newport Beach, Calif, 

 and in commercial anchovy fishing grounds near 

 Los Angeles Harbor (author unpubl. data) con- 

 tained many more anchovies (approximately 10- 

 20/individual) than did sharks sampled in the 

 Catalina study area. The two former areas feature 

 nearshore submarine escarpments where the size 



and concentrations of anchovy schools were 

 among the greatest anywhere in southern 

 California (Mais 1974). 



The present status of the blue shark-anchovy 

 association may be the aftermath of a previously 

 more complex predator-prey web. Southern 

 California commercial fisheries have severely de- 

 pleted Scomber japonicus and Pacific sardine, 

 Sardinopa sagax, populations (MacCall et al. 

 1976), both natural prey for blue sharks (author 

 unpubl. data). Although such declines in major 

 forage species may have resulted in increased 

 predation on anchovies, the southern California 

 population is apparently in little danger of over- 

 exploitation by commercial fisheries or pelagic 

 fish predators (Pinkas et al. 1971; Mais 1974; 

 MacCall et al. 1976). 



Fishes associated with inshore habitats were 

 also taken by sharks. Jack mackerel, Trachurus 

 symmetriciix, are widely distributed throughout 

 the Gulf of Alaska (Miller and Lea 1972), and 

 inhabit both inshore and pelagic habitats (Feder 

 et al. 1974). In southern California waters, adults 

 of this species generally aggregate near the bot- 

 tom or under kelp forests at rocky banks and shal- 

 low coastal areas during daylight and venture into 

 deeper waters at night. Only rarely do jack mack- 

 erel form sizeable surface schools in the open sea 

 (Mais 1974). Similarly, smaller jack mackerel 

 (e.g., near 25 cm TL), common at inshore areas of 

 Catalina, swam along the outer edges of kelp beds 

 during the day in closely spaced schools and some- 

 times aggregated within the kelp forest proper. At 

 night jack mackerel occurred in open waters 

 (away from kelp) often interspersed with Scomber 

 japonicus. Larger pelagic individuals might rep- 

 resent a schooling prey source for blue .sharks in 

 open waters, but stomach content data indicate 

 this was not the case near Catalina. Neave and 

 Hanavan (1960) described concurrent expansion 

 of blue shark and jack mackerel ranges in the Gulf 

 of Alaska during the summer, although no data 

 was presented on possible predator-prey interac- 

 tions. 



Pipefish were the second most frequent fish prey 

 for sharks in this study and a principal prey for 

 blue sharks off Newport Beach (Bane 1968 1, but 

 because of their small biomass must be regarded 

 as a prey species of minor importance. Free- 

 swimming pipefish were observed at the surface in 

 open water (far from surfgrass or kelp beds) at 

 night, among flotsam kelp during daylight, and 

 during daytime scuba dives in kelp forest and 



180 



