BRODEUR and PEARCY: FOOD HABITS AND DIETARY OVERLAP OF SOME SEBASTES 



pelagic fishes and sergestid shrimps were common 

 but generally contributed little to the diet on a 

 weight basis. 



The northernmost region showed reduced occur- 

 rences of euphausiids, overall, but they still com- 

 posed a percent weight equivalent to the two 

 southern areas. This could have resulted from a 

 shift to T. spinifera, which is generally larger 

 than E. pacifica, as the main euphausiid con- 

 sumed. Decapods were of lesser importance, but 

 gelatinous zooplankton were very common in the 

 stomachs of fish from this region. This may 

 explain the high abundances of hyperiid amphi- 

 pods known to be associated with gelatinous 

 zooplankton. Fishes were common, especially ju- 

 venile Pacific sand lance, Ammodytes hexapterus, 

 a prey species found only in the stomachs collected 

 from this area. 



Sebastes flavidus showed a different pattern in 

 food utilization. A general decrease in euphausiid 

 abundance was observed with increasing latitude 

 (Table 12). The euphausiids from the southern- 

 most regions were mostly E. pacifica, although 

 many were unidentified. The only other important 

 prey groups in these southern regions were cepha- 

 lopods (mostly Loligo opalescens) and relatively 

 large fishes such as Pacific herring and mycto- 

 phids iDiaphus theta ). All other prey groups were 

 common but made little contribution to the diet. 



Specimens of S. flavidus collected in the north- 



ernmost regions consumed substantial amounts of 

 fish (mainly clupeids and myctophids). Euphau- 

 siids were relatively unimportant in these re- 

 gions. As was the case with S. pinniger, T. 

 spinifera was the dominant euphausiid eaten 

 in the Washington-Vancouver region. Decapods, 

 consisting mostly of Pandalus jordani, reached 

 their highest proportion of the diet in the north- 

 ernmost region. 



Diel Variation 



Both species showed variation in prey composi- 

 tion with the diel period (Table 13). Sebastes 

 pinniger contained high percentages of euphau- 

 siids by weight during all four diel periods, with 

 highest percentages occurring in the afternoon 

 periods. Fishes, mostly non-mesopelagic species, 

 were most important on a weight basis during 

 morning and night when they occurred least fre- 

 quently. Euphausiids were relatively more impor- 

 tant by weight in the two afternoon periods. A 

 high proportion of the fishes found in the stomachs 

 during the afternoon periods were mesopelagic 

 species. 



Sebastes flavidus exhibited the opposite trends 

 in food consumption with respect to time of day. 

 Euphausiids were found in the highest propor- 

 tions by weight during the morning and night 

 periods while proportions of fish were substan- 



TABLE 13. — Variation in major prey taxa composition with time of day for Sebastes pinniger and S. flavidus. F.O. = frequency of 

 occurrence; 7c W = percent gravimetric composition; + = a prey category was present but made up < 0.195 of the total weight. 



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