IMPORTANCE OF FAR-OFFSHORE SAMPLING IN EVALUATING THE ICHTHYOPLANKTON COMMUNITY IN THE NORTHERN CALIFORNIA CURRENT

The distribution and concentration of ichthyoplankton were examined from stations extending 2–364 km offshore at 7–53 km intervals along the Newport Hydrographic (NH) and Crescent City (CC) (July 2008 only) lines in the northern California Current (NCC) during March, April, and October 2007, and March, June, and July 2008. A total of 2372 fish larvae representing 36 taxa from 22 families were collected in 72 bongo samples from 30 stations: 15 stations were “shelf ” (<2000 m depth), 15 were “far-offshore” (>2000 m depth). Four dominant taxa accounted for 90% of the total larval fish concentration:Stenobrachius leucopsarus (47%),Sebastes spp. (25%), Engraulis mordax (12%), and Tarletonbeania crenularis (6%). Mean study-wide concentrations of the dominant taxa were significantly greater in the far-offshore region than in the shelf region. Weighted mean length was significantly greater only for larval Sebastes spp. collected at the far-offshore compared with the shelf stations, while E. mordax larvae were only collected at far-offshore stations in June and July 2008. Larval distributions and concentrations were also examined in relation to variable local environmental factors (i.e. temperature, salinity, dissolved oxygen, fluorescence, and east-west Ekman transport) and basin-scale indices (i.e. MEI and PDO). Historic and ongoing survey designs used to characterize the plankton community in the NCC have usually incorporated only coastal and shelf (<~100 km offshore) stations extending out to the continental slope (~2000 m depth). Increased sampling effort at far-offshore stations will be required to adequately characterize the ichthyoplankton community of the NCC in the future. INTRODUCTION Ichthyoplankton surveys have long been recognized as cost-effective proxies to identify spawning locations, success, environmental requirements, essential fish habitat, and recruitment potential of marine fish stocks (Hunter et al. 1993; Houde 1997; Lyczkowski-Shultz 2006), as well as providing ecosystem indicators of environmental change (Brodeur et al. 2008) and an understanding of trophic interactions between zooplankton and important piscivores (Hunter and Kimbrell 1980). However, by focusing their sampling efforts almost exclusively on near-shore and shelf waters while neglecting to sample far-offshore waters beyond the continental slope, these surveys may not adequately sample the entire, or even primary, cross-shelf range of the dominant larval taxa of interest. During the past 40 years,most ichthyoplankton studies conducted in the northern California Current (NCC) have focused on fish eggs and larvae collected inshore of the continental slope (Richardson and Pearcy 1977; Richardson et al. 1980; Mundy 1984; Boehlert et al. 1985; Brodeur et al. 1985;Auth and Brodeur 2006;Auth et al. 2007; Auth 2008; Brodeur et al. 2008; Parnel et al. 2008). Only three NCC studies have hitherto incorporated far-offshore ichthyoplankton samples: Waldron 1972, Richardson 1973, and Doyle 1992. However, Waldron 1972 only sampled during two months (April and May) in 1967, whereas Richardson 1973 only sampled from May to October in 1969 and only differentiated sampling effort between near-shore (<37 km from shore, ~150 m in depth) and broadly-defined offshore (37–425 km from shore, ~150–3000 m in depth) stations. Doyle 1992 reported on general ichthyoplankton densities from the NCC in 1980–87, but did not conduct any testable statistical analyses of cross-shelf distributions and concentrations. During the two decades since the completion of Doyle’s 1992 work, the NCC has experienced extreme and variable climate-induced environmental fluctuations, including multiple shifts between warm and cold regimes, El Niño and La Niña events, variability in seasonal upwelling intensity, and change in biological communities (Schwing and Moore 2000; Peterson and Schwing 2003; Brodeur et al. 2006;Hooff and Peterson 2006) that may have altered the cross-shelf distribution of the ichthyoplankton community in the region.However, all studies during that time, including the on-going National Marine Fisheries Service (NMFS) Stock Assessment Improvement Plan (SAIP),U.S.Global Ocean Ecosystem Dynamics Program (GLOBEC), and Pacific Coast Ocean Observing System (PaCOOS) monitoring projects, have focused on collecting plankton samples primarily from 107 Auth lo final:• CALCOFI SETUP 11/28/09 4:53 PM Page 107