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Fishery Bulletin 90(3). 1992 



In that year, latitude had no discernible influence on 

 the diet of these two species, although for shortbelly 

 rockfish a significant interaction between depth and 

 latitude was evident. These findings strongly suggest 

 that spatial variability in the environment (i.e., latitude 

 and depth of the water column) can influence, to some 

 extent, the diets of pelagic juvenile rockfish in a species- 

 specific manner. 



Results for the full time-series of shortbelly rockfish 

 data (1984-87) also show that spatial patterns change 

 over time. Although depth had a highly significant ef- 

 fect on diet in 1986 and 1987, it was not significant in 

 1984 or 1985. Similarly, latitude had no appreciable 

 relationship to the diet of shortbelly rockfish in 1985 

 and 1987, but it had a highly significant effect in 1986. 

 Importantly, whenever a latitude correlation with diet 

 was present, the interaction term (depth * latitude) was 

 significant as well. We believe that the erratic influence 

 of spatial structure on the shortbelly diet is likely due 

 to the dynamic nature of the nearshore pelagic/neritic 

 physical environment. 



Using the 1987 data, we examined the least-squares 

 means (Searle et al. 1980) of the transformed numerical 

 proportions of the individual prey types to learn exactly 

 how dietary composition varied when statistically- 

 significant model effects occurred. In that year, the 

 diet of chilipepper showed borderline significance with 

 depth (P = 0.058); the least-squares means revealed that 

 chilipepper consumed more Calanus spp. copepods in 

 shallow water, and more juvenile copepods and juvenile 

 euphausiids at bottom depths >100m. Likewise, all 

 three prey types {Calanus spp., euphausiid eggs, and 

 juvenile euphausiids) of widow rockfish were consumed 

 in greater proportion in deep water, especially euphau- 



siid eggs. For shortbelly rockfish, which displayed a 

 significant interaction term, consumption of Calanus 

 spp. copepods was noticeably depressed at shallow 

 southern stations. Euphausiid eggs were consumed in 

 much greater quantities at deep stations, both north 

 and south, while fewer larval euphausiids (furcilia and 

 calyptopis) were found in fish from northern deep 

 stations. 



Predator size 



Results were inconsistent when these same data (i.e., 

 numerical proportions in the diet of the three most fre- 

 quently occurring prey items for 1984-87 shortbelly 

 rockfish, 1987 chilipepper, and 1987 widow rockfish) 

 were also explored with MANOVA to assess the effect 

 of fish size on composition of the diet. In each instance, 

 fish were assigned to either small or large size-classes, 

 based on whether standard lengths were smaller or 

 larger than the annual median of that species. 



Of the six cases examined (Table 8) two yielded 

 significant (P<0.05) results. Large shortbelly rockfish 

 sampled in 1986 tended to eat a higher proportion of 

 Calanus spp. copepods, whereas small fish had a higher 

 fraction of juvenile euphausiids and juvenile copepods 

 in their diet. Results from that year, therefore, sup- 

 port the view that large fish tend to consume large 

 prey. Even so, a significant size effect was demon- 

 strated for 1985 shortbelly rockfish, which was exact- 

 ly the opposite of 1986; large fish consumed fewer 

 Calanus spp. copepods and a greater percentage of 

 euphausiid eggs than did small fish. Sample size was 

 not adequate to statistically analyze fish length jointly 

 with distributional patterns. However, in 1985, 34 of 



