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



TABLE 8. — Summary of darkblotched rockfish, Sebastes cra- 

 meri, stomach contents from the National Marine Fisheries 

 Service's summer sampling. F.O. = frequency of occurrence. 



pinniger, S. diploproa, and S. alutus are all rela- 

 tively high (0.58, 0.56, and 0.61, respectively). 



Overlaps between S. pinniger and S. flavidus 

 for the seasonal cruises are similar to the results of 

 the summer surveys (dh = 0.80 by number; 0.46 

 by weight). A possible explanation for the lower 

 values may be changes in availability of both 

 predator and prey (i.e., no S. flavidus stomachs 

 were collected during spring and early summer 

 when the euphausiid populations are generally 

 the highest). The variability associated with the 

 different cruises was examined by calculating the 

 overlaps between these two species for the four 

 seasonal cruises that contained at least 10 speci- 

 mens of each species. The July cruise had the 

 highest overlap of all on a weight basis (dh = 

 0.88) and the September cruise had the lowest 

 (dh = 0.32), while the December and January 

 cruises had intermediate overlaps (dh = 0.52 

 and 0.46), suggesting seasonal variations in prey 

 availability for these species. 



For comparative purposes, the dietary composi- 



TABLE 9. — Principal prey types making up >1.09t of the diet and food breadths of the five 

 species of Sebastes. R is the total number of distinct prey items identified to at least genus 

 level and that make up 0.1' < ip, 0.0011 of the identified fraction of the total weight. These 

 prey were used to calculate the overall diet breadth (B i and the evenness of distribution of 

 the prey items in the diet iB n I. The seasonal values for S. flavidus and S. pinniger are given 

 in parentheses. 



S. pinniger and S. flavidus, although the diets 

 are not similar for other prey items. 



Overlap on the basis of weight, which may be a 

 better measure of the energy obtained from the 

 various food items, indicates high overlap be- 

 tween S. pinniger and S. diploproa and between 

 S. alutus and S. pinniger, S. diploproa, and S. 

 crameri. The rest of the values were <0.60, in- 

 cluding S. pinniger with S. flavidus (dh = 0.48). 

 The diet of S. flavidus overlaps the least with the 

 other species (dh = 0.42) mainly due to its more 

 piscivorous habits. The mean overlap values of S. 



tion of the five most important prey categories for 

 each of the rockfish species is presented by percent 

 number and percent weight in Figures 4 and 5. 

 Both figures show the importance of euphausiids 

 in all five species. The stomachs of S. crameri 

 contained a more equitable distribution of num- 

 bers of the major prey groups than the other 

 species of rockfishes, with higher proportions of 

 amphipods and copepods. Some of this difference 

 may be ascribed to the smaller sample size. On a 

 weight basis, S. flavidus was unique in that fishes 

 and cephalopods were of greater importance in the 



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