(Table 2). The high index for L. opalescens in 

 January 1976 reflected the squid's extensive 

 winter spawning assemblages in the study area, 

 and similarly is the reason for its high annual 

 rank (Table 1 ). Histioteuthid squid were probably 

 the most significant cephalopod prey for sharks in 

 more oceanic waters away from inshore spawning 

 aggregations of L. opalescens. The low average 

 number of anchovies and histioteuthid squid per 

 stomach and the relatively small coefficients of 

 dispersion for these two prey indicate that sharks 

 obtained them somewhat regularly over a wide 

 area (Table 3). Conversely, the large coefficient for 

 market squid during its spawning season concurs 

 with observations that this prey was taken from 

 large schools during its spawning runs at inshore 

 areas. 



Digestive rate tests for healthy, captive sharks 

 were in order with digestive states of prey recov- 

 ered from wild sharks. Anchovies removed from 

 captive sharks at 6 h after feeding were easily 

 identified, and showed only preliminary digestion 

 of fins and margins of the opercula. Likewise, 

 whole squid were easily recognized and had only 

 slight signs of external surface decomposition. At 

 12 h after feeding, digestion of anchovies was 

 characterized by decomposed abdominal walls, 

 moderate scale loss, and some skin deterioration. 

 Digestion of squid was still negligible. At 24 h, 

 anchovies were well digested with only vertebrae, 

 otoliths, and small sections of muscle present. 

 Squid heads were separated from the body and 

 lenses had detached from the optic cups, but beaks 

 were still implanted within the buccal mass. In 

 general, digestive rates were at least twice as fast 

 for anchovies than for squid. 



Times of normal feeding activity were estimated 

 by comparing the digestive rate data obtained 

 from captive sharks with recognizable anchovies 

 recovered from wild sharks. Anchovies that were 



FISHERY BULLETIN: VOL. 77. NO. 1 



Table 3. — Dispersion of the three major prey species in blue 

 shark stomachs off Santa Catalina Island, Calif. Means for mar- 

 ket squid were computed for squid spawning season (Mar. 1975, 

 Dec. -Jan. 1976) and nonspawning season (Apr. -Nov. 1975, Feb. 

 1976). Coefficients of dispersion (ratioof variance to mean) indi- 

 cate grouping of prey among stomachs. A coefficient of 1 de- 

 scribes a random distribution. Larger coefficients describe in- 

 creasingly contagious (clumped) distributions of prey among 

 shark stomachs (Sokal and Rohlf 1969). 



freshly ingested predominated in sharks captured 

 in early morning hours (Figure 4) and corres- 

 ponded to a duration of approximately 0-8 h after 

 ingestion. Moderately digested anchovies were 

 prevalent in sharks sampled in the afternoon and 

 represent anchovies held about 9-20 h after con- 

 sumption. 



Tooth marks on anchovies recovered from wild 

 sharks indicate that prey were almost exclusively 

 captured from behind. When present, tooth marks 

 were usually located on the posterior lateral one- 

 third of the anchovy, and in many cases impres- 

 sions penetrated only the skin and not the 

 myotome. 



The movements of four sharks were monitored 

 using ultrasonic telemetry in the winter 

 (October-February) and supplement the spring, 

 summer, and fall trackings of a previous study in 

 the same area (Sciarrotta and Nelson 1977). 

 Sharks ranged over wide areas (e.g., approxi- 

 mately 50 km- in 18 h: Tracking 2) and did not 

 exhibit movements oriented towards the island 

 shore. Vertical movements, except for the initial 

 plunge immediately following tag application, 

 were confined to the upper 15-m depth range. 



T..\BLE 2. — Monthly index of relative importance URI) of identilii'd cephalopod prey in stomachs of blue sharks near Santa Catalina 



Island, Calif. See caption of fable 1 for calculation oflRI. 



178 



