Miller and Brodeur: Diets of and trophic relations among dominant marine nekton within the northern California Current ecosystem 



553 



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i, © 



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Nekton species 



Blue shark 

 Coho salmon (a) 



y////////A 



Chinook salmon (y) 



Coho salmon (y) 



Chinook salmon (a) 



Jack mackerel 



Pacific saury 



Pacific sardine 



y/A"/////////^^^^^ 



v//////////////////^^^^^ 



m^^^^^^^^^(/^^^K ^^ ^^>>^^^^^^^^^^ 



Pacific herring 



Whitebait smelt 



Sablefish (j) 



Steelhead trout (J) 



V/////////////////^^^^^ 



I Nekton prey 



I I Osteichthyes (a) 

 Osteichtliyes(l-ji 

 I Ceptialopoda 



[ I Crustacea 



Euphausiidae 

 Decapoda (I) 

 Brachyura (I) 

 H\pcriidca 

 Copepoda 

 Cnidaria (I) 

 Ptivloplaiiklon 



V////////////////////////^^^^^ 



I I Other 



'^z^///////////A^/y/^z^ 



■IL^^ 



y/////////////////////////^^^^^ 



Chmook salmon (sy) 

 Cutthroat trout 



-^^ZV/Z///////////////^^^^^ 



steelhead trout (a) y///////////yZ/ ///////////^^^^^ 



Pacific mackerel m////////////////////////^^^^^ 



Northern anchovy V/////////////////////^^^^^ 



LingcodC) ^/Zy^ZZ^Z^Z/>Z/Z>Z^ZZZ/Z^^^ 



Rockfish(_i) L-.-. 



7?TTT■T■T■J^^J r-j— 5"T-j ^^^^^^^^^!■^^l^^l5^^^^^^!■^ 



Yeiiowiaii rockfish (j) |■^^^^^^^^^^^^^^^^^^^^^'v^^^^^^^^^ >>>*>' '>'>>'■>>>" : 



DarkblotchedrockfishG) ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 



25 50 



Wet weight (% ) of diet 



75 



100 



Figure 2 



Summary of nekton diets analyzed from June and August 2000 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 (from top to bottom) are the following: blue shark iPrionace glauca). coho 

 salmon iOncorhynchus kisutch), chinook salmon (O. tshawytschal, jack mackerel (Trachurus symmetricus). Pacific saury 

 {Cololabis saira). Pacific sardine iSardinops sagax). market squid iLoligo opalescens), surf smelt tHypomesus pretiosus). 

 Pacific herring tClupea pallasi). whitebait smelt iAllosmerus elongatus). sablefish iAnoplopoma fimbria), steelhead trout 

 (O. mykiss), cutthroat trout (O. clarki). Pacific mackerel {Scomber japonicus), northern anchovy [Engraulis mordax), ling- 

 cod (Ophiodon elongatus), rockfish (Sebastes spp.), yellowtail rockfish (S. flavidus), darkblotched rockfish (S. crameri). 

 Life history stages of nekton are shown in parentheses: j = juvenile; sy = subyearling; y = yearling, and a = adult; nekton 

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



revealed general trophic groups that primarily con- 

 sumed adult Osteichthyes, larval-juvenile Osteichthyes, 

 euphausiids, mixed zooplankton, and copepods; however, 

 in each trophic group omnivory was expressed and actu- 

 ally predominated in some nekton trophic groups. The 

 importance of omnivory in the higher trophic group of 

 blue shark and adult coho salmon indicated that the typi- 

 cal mid-trophic level taxa, such as anchovy and Pacific 

 sardine, were sometimes bypassed for direct feeding on 



large zooplankton, in particular adult euphausiids. Pre- 

 vious studies from the NCC system have also shown that 

 blue shark (Brodeur et al., 1987; Harvey, 1989), adult 

 coho (Brodeur et al., 1987), and adult chinook (Hunt et 

 al., 1999) salmon feed on adult nekton and euphausiids. 

 With the exception of Pacific hake, top-down trophic 

 pressure from fish may be less influential in the NCC 

 because top nekton predators are not as abundant in 

 this system as nekton prey such as euphausiids (Ressler 



