554 



Fishery Bulletin 105(4) 



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Nekton species 



Blue shark 



Pacific hake 



Chinook salmon (a) 



Coho salmon (al 



.lack mackerel 



Northern anchovv 



Pacific herring 



Sablefish(_j) 



Whitehall smelt 



Chinook salmon (y) 



Coho salmon (y) 



Steelhead trout (j ) 



Chum salmon (j) 



Market squid 



Pacific sand lance 



Surf smelt 



Spiny doijfish 



Pacific sardine 



Widow rockfish (j) 



Pacific saury 



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Lingcod (j) 



Rockfish (j) 



Darkblotched rockfish (j ) 



Canary rockfish (j) 



Bank rockfish (j) 



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y/z<^y^<^^^^z^>>yy^<^^y<^^^ 



Nekton prey 



^1 Osteichth\cs(a) 



^1 Osteichthyes (l-j) 



^1 Osteichthv es ( tissue ) 



\^,\ Cephalopoda 



[ ] Crustacea 



l/yj Euphausiidae 



I — I Decapoda ( I ) 



[jJH Brachyura(l) 



Y(-\ M> peri idea 



I ] Copepoda 



[X^ Cnidaria(l) 



|;:;] Gelatinous 



zooplankton 



^;^ Ptiytoplankton 



[jUj tlnidenlified 



I I Other 



25 50 



Wet weight (%) of diet 



75 



100 



Figure 3 



Summary of nekton diets analyzed from June and August 2002 northern California Current GLOBEC (GLOBal ocean 

 ECosystems dynamics) cruises. Trophic groups based on cluster analysis of diets (percent wet weight) are blocked and 

 labeled (A) to (E). Species not blocked lacked sufficient numbers and frequency of occurrence for analysis. Scientific names 

 of species in the order they appear in the figure are the following: blue shark (Prionace glauca). Pacific hake {Merluccius 

 productus), Chinook salmon [Oncorhynchus tshawytscha), coho salmon (O. kisutch), jach mackerel (Trachurus symmetri- 

 cus), northern anchovy (Engraiilis mordax). Pacific herring iClupea pallasi). sablefish (Anoplopoma fimbria), whitebait 

 smelt (Allosmerus elongatus), steelhead trout (O. mykiss), chum salmon (O. keici), market squid (Loligo opalescens), Pacific 

 sand lance iAmmodytes hexapterus), surf smelt iHypomesiis pretiosus). spiny dogfish iSqualus acanthias), Pacific sardine 

 iSardinops sagax), widow rockfish (Sebastes entomelas). Pacific saury iCololabis saira), lingcod iOphiodon elongatus), 

 rockfish (Sebastes sp.), darkblotched rockfish (S. crameri), canary rockfish (S. pinniger), and bank rockfish (S. rufus). 

 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. 



et al., 2005). Pacific hake likely represent the largest 

 pretiatory biomass off the west coast of North America 

 (Methot and Dorn, 1995). They feed on adult nekton 

 (Brodeur et al., 1987; Emmett and Krutzikowsky, in 

 press) but also extensively on euphausiids (Brodeur et 

 al., 1987; Tanasichuk, 2002) and give evidence that as 

 omnivores they may not impose direct and intensive 

 trophic pressures upon adjacent trophic species in this 



upwelling ecosystem, as would be implied by the classi- 

 cal theory of top-down control. 



Euphausiids were also observed as important prey of 

 many middle-trophic-level nekton species. Three trophic 

 groups were evident at this trophic level; 1) a group of 

 species that consumed predominantly larval-juvenile fish 

 and to a lesser degree euphausiids, 2) a group of species 

 that consumed mostly euphausiids, and 3) a group of 



