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



555 



species that fed on euphausiids and other 

 mixed zooplankton. Although these trophic 

 groups were formed for both years, trophic 

 group membership changed, and many of 

 nekton shifted between the consumption 

 of euphausiids and other zooplankton prey. 

 The importance of euphausiids in the diets 

 of mid-trophic nekton species agreed with 

 observations by Brodeur et al. (1987), and 

 with results that showed the importance 

 of larval-juvenile fishes in diet studies of 

 jack mackerel (Brodeur et al., 1987) and 

 juvenile salmonids (Brodeur and Pearcy, 

 1990). Nekton secondary consumers, those 

 feeding on copepods, euphausiid eggs and 

 furcilia, consisted of juvenile rockfishes 

 {Sebastes spp. ) and Pacific sardine. How- 

 ever, some species of juvenile rockfish 

 (widow and darkblotched) and juvenile 

 lingcod also consumed larger prey, such 

 as adult euphausiids, and other larval- 

 juvenile fishes (Reilly et al., 1992). Pacific 

 sardine have been observed to be highly 

 euryphagous, feeding on phytoplankton, 

 copepods, and euphausiids (Hand and Ber- 

 ner, 1959). Little information is available 

 on the diets of juvenile rockfish species 

 and juvenile lingcod; many of these species 

 also showed a diverse size-range of prey, 

 consuming copepods, egg-adult stages of 

 euphausiids and, as in juvenile lingcod, 

 other larval-juvenile fishes. Various life 

 stages of euphausiids and larval-juvenile 

 fishes therefore played an important role 

 in the diets of many nekton at the time 

 of this study, indicating that most nek- 

 ton were feeding at or near the secondary 

 consumer level. 



The substantial contribution of euphau- 

 siids to many nekton species may have 

 been due to recent increases in euphau- 

 siid abundance after 1999 within the NCC 

 pelagic ecosystem. Feinberg and Peterson 

 (2003) observed an extension in the sea- 

 son of euphausiid spawning and multiple 

 peaks in egg density starting in 1999, 

 presumably when there was a regime 

 shift to higher upwelling and primary 

 and secondary production (Peterson and 

 Schwing, 2003). In a trophic study of the 

 NCC system during the 1980s, Brodeur 

 and Pearcy (1992) also observed higher 

 dietary overlap among different nekton 

 species during high upwelling years, and 

 that much of the overlap was attributed to 

 euphausiids. Moreover, they observed that 

 nekton showed lower dietary overlap and 

 increased foodweb complexity during the 

 1983 El Nino, a period of low upwelling 

 and primary and secondary production. 



