552 



Fishery Bulletin 105(4) 



Year 2000 '^^ 



Blue shark 



Coho salmon (a) 



Chinook salmon (yi 



Coho salmon (yi 



Chinook salmon (a) 



Jack mackerel 



Pacific saury 



Pacific sardine 



Market squid 



Surf smelt 



Pacific herring 



Whitebait smelt 



Sablefishljt 



Steelhead trout (jt 



Information remaining {%) 



15 50 25 



B 



Year 2002 



Blue shark 



Pacifi 



Chinook salmon (a 



Coho salmon la) 



Jack mackerel 



Northern anchovy 



Pacific hemng 



Sablefish(ji 



Whitebait smelt 



Chinook salmon ly) 



Coho salmon (y) 



Steelhead trout (j) 



Chum salmon ijl 



Market squid 



Pacific sand lance 



Surf smell 



Spiny dogfish 



Pacitlc sardine 



Widow rockfish (j) 



Pacific saury 



; shark t 



c hake -I I 



h 



-<A> 



-<§> 



-(£> 



3- 



D- 





Figure 1 



Dendrograms of nekton based on diet (percent wet weight contribution 

 of prey) as determined by agglomerative hierarchical cluster analysis 

 of nekton collected from the northern California Current during June 

 and August 2000 and 2002 GLOBEC (GLOBal ocean ECosystems 

 dynamics) cruises. Dashed line denotes the level (percent information 

 remaining) at which trophic groups were established in the dendro- 

 gram. The percent information remaining is a function of the amount 

 of information lost at each step of hierarchical cluster analysis. Scien- 

 tific names of the species in the order they appear in the figure (from 

 top to bottom) are the following: blue shark iPrionace glauca), coho 

 salmon (Oncorhynchus kisutch), chinook salmon (O. tshawytscha), jack 

 mackerel I.Trachurus symmetricus) , Pacific saury (Cololabis saira). 

 Pacific sardine (Sardinops sagax), market squid (Loligo opalescens). 

 surf smelt {Hypomesus pretiosus). Pacific herring (Clupea pallasi), 

 whitebait smelt iAHosmeriis etongatus), sablefish iAnoplopoma fimbria), 

 steelhead trout (O. mykiss). Pacific hake (Merluccius productus). north- 

 ern anchovy iEngraulis morda.x). chum salmon (O. keta), Pacific sand 

 lance {Ammodytes hexapterus), spiny dogfish iSqualus acanthias), and 

 widow rockfish (Sebastes entomelas). Life history stages of nekton are 

 shown in parentheses: j = juvenile, y= yearling, and a = adult; nekton 

 and prey with no indication of life history stage are adult. 



salmon and blue shark, to adult Osteich- 

 thyes (Fig. 2). 



In 2002, trophic group C containing 

 yearling chinook and coho salmon, juve- 

 nile chum salmon, and steelhead trout 

 had the highest overall mean percent sim- 

 ilarity (63%); and the highest similarity 

 (78%) was between yearling chinook and 

 yearling coho salmon (Table 3) . Most of 

 the similarity in diet within this trophic 

 group was due to larval-juvenile Osteich- 

 thyes (70% of total similarity). Trophic 

 groups B and A had the next highest 

 similarities in diet (mean 61% and 46%, 

 respectively). Similarities in diet within 

 these two groups were primarily attribut- 

 ed to euphausiids (that represented 68% 

 of total similarity) for trophic group B, 

 and adult Osteichthyes (that represented 

 58% of total similarity) for trophic group 

 A. The remaining trophic groups D and E 

 had percent similarities <30%'. 



Interannual variation 



Adult coho salmon and juvenile steelhead 

 trout displayed the largest contrast in diet 

 between 2000 and 2002. For adult coho 

 salmon, adult and larval-juvenile Ostei- 

 chthyes contributed >95% of the diet in 

 2000, and brachyuran larvae contributed 

 approximately 50% of the diet in 2002 

 (Fig. 4). Steelhead trout had a greater 

 proportion of its diet from euphausiids 

 (84%) in 2000, whereas larval-juvenile 

 Osteichthyes were more important in 2002 

 (57%). The remaining nekton displayed 

 relatively similar diets between years, 

 although differences were observed in the 

 contribution of euphausiids and brachy- 

 uran larvae. Yearling coho and chinook 

 salmon showed that larval-juvenile fishes 

 contributed >70% of their diet for both 

 years. Euphausiids contributed more to 

 diets of both species during 2000 (>18%') 

 compared to 2002 (>5%), whereas in 2002 

 brachyuran larvae were more prominent 

 in the diets (Fig. 4). The trend of higher 

 proportions of euphausiids in diets in 2000 

 and of brachyuran larvae in 2002 was 

 also observed in adult coho and chinook 

 salmon. 



Discussion 



Trophic groups 



Diet analysis of 26 nekton species of the 

 northern California Current ecosystem 



