548 



Abstract — In this study we analyzed 

 the diets of 26 nekton species collected 

 from two years (2000 and 2002) off 

 Oregon and northern California to 

 describe dominant nekton trophic 

 groups of the northern California Cur- 

 rent (NCC) pelagic ecosystem. We also 

 examined interannual variation in the 

 diets of three nekton species. Cluster 

 analysis of predator diets resulted in 

 nekton trophic groups based on the 

 consumption of copepods, euphau- 

 siids, brachyuran larvae, larval- 

 juvenile fishes, and adult nekton. 

 However, many fish within trophic 

 groups consumed prey from multiple 

 trophic levels — euphausiids being the 

 most widely consumed. Comparison of 

 diets between years showed that most 

 variation occurred with changes in 

 the contribution of euphausiids and 

 brachyuran larvae to nekton diets. 

 The importance of euphausiids and 

 other crustacean prey to nekton indi- 

 cates that omnivory is an important 

 characteristic of the NCC food web; 

 however it may change during peri- 

 ods of lower or higher upwelling and 

 ecosystem production. 



Diets of and trophic relationships 

 among dominant marine nekton within 

 the northern California Current ecosystem 



Todd W. Miller (contact author)' 

 Richard D. Brodeur^ 



Email address for T. W. Miller: millertw@dpc.ehlme-u,ac,|p 



' Cooperative Institute for Marine Resources Studies 

 Oregon State University 

 Newport, Oregon 97365 



Present address: Center lor Manne Environmental Studies (CMES) 

 Ehime University, 2-5 Bunkyo-cho, Matsuyama 

 Ehime, 790-8577, Japan 



2 National Oceanic and Atmospheric Administration 

 National Marine Fisheries Service, Northwest Fisheries Science Center 

 Hatfield Marine Science Center 

 Newport, Oregon 97365 



Manuscript submitted 23 February 2007 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 5 July 2007 by the Scientific Editor. 



Fish. Bull. 105:548-559 (2007). 



Eastern Pacific boundary upwelling 

 zones, such as the California Cur- 

 rent, are generally highly productive 

 and support major fisheries, yet these 

 ecosystems also exhibit substantial 

 temporal fluctuations in primary and 

 higher-level production (Francis and 

 Hare, 1994; Carr, 2002; Chavez et al., 

 2003). This variation has been attrib- 

 uted to variability in abiotic forcing 

 through relatively short-term (inter- 

 annual) El Nino and La Nina events 

 (Pearcy and Schoener, 1987), as well 

 as long-term (decadal) environmen- 

 tal forcing (Francis and Hare, 1994; 

 Mantua et al., 1997). This apparent 

 link between abiotic forcing and the 

 ecosystem has led to considerable dis- 

 cussion regarding energy flow through 

 large marine ecosystems (Jackson 

 et al., 2001). However, few studies 

 have comprehensively examined mul- 

 tispecies trophic patterns within a 

 system. Understanding trophic pat- 

 terns and temporal changes between 

 species across multiple trophic groups 

 is essential in understanding energy 

 transfer within a system and mech- 

 anisms behind ecosystem stability 

 (Worm and Duffy, 2003). 



The northern California Current 

 (NCC) system encompasses the north- 

 ern region of the California Cur- 

 rent production zone (approximately 

 41-49° N) along the continental shelf 

 and shelf break between northern 



California and Washington. This 

 system is a major upwelling region, 

 where Pacific sardine (Sardinops 

 sagax), northern anchovy (Engraulis 

 mordax), jack mackerel (Trachurus 

 symmetricus), market squid (Loligo 

 opalescens), and Pacific hake (Mer- 

 luccius productus) are the domi- 

 nant nektonic species (Brodeur and 

 Pearcy, 1986; Brodeur et al., 2005). 

 Between April and September, strong 

 but episodic coastal upwelling is the 

 dominant hydrographic feature of the 

 NCC. This upwelling provides cool 

 nutrient-rich water to the euphotic 

 zone across the shelf (Huyer, 1983), 

 allowing for high levels of primary 

 production (Hood et al., 1991). Inter- 

 annual variation in coastal upwell- 

 ing, particularly between El Nino 

 and La Nina events, greatly influ- 

 ences primary production (Corwith 

 and Wheeler, 2002) and higher tro- 

 phic levels (Ainley et al., 1996). On 

 an interdecadal scale, the California 

 Current also experiences production 

 regimes of 30 years or more, which 

 have been linked to salmon survival 

 (Mantua et al., 1997) and variation in 

 NCC zooplankton biomass (McGowan 

 et al., 1998). 



The diets of multiple species within 

 the NCC pelagic ecosystem have been 

 examined in only a few studies, and 

 these studies were mostly performed 

 on single or a few closely related spe- 



