Abundance and diversity of coastal fish larvae as indicators of recent changes in ocean and climate conditions in the Oregon upwelling zone

Abstract

We examined ichthyoplankton sampled from 2 stations, 9 and 18 km offshore of Newport, Oregon, USA, over a decade of cruises every 2 wk from 1996 to 2005. The 10 most dominant taxa comprised approximately 87.3% of the total catch. Concentration of fish larvae was highest in January to March, whereas diversity peaked from March through May. Both overall diversity and density of larval fishes were relatively constant throughout the period of 1996 to 2003, with a dramatic decrease in these metrics since 2004, especially for winter-spawning (January−May) species. During cool years (1999−2002), the assemblage was dominated by northern or coastal taxa such as sand lance Ammodytes hexapterus, sanddabs Citharichthys spp., and smelts Osmeridae, whereas in warm years (2003−2005), southern or offshore taxa such as English sole Parophrys vetulus, northern anchovy Engraulis mordax, and rockfishes Sebastes spp. were more abundant. These changes were related to concurrent shifts in the zooplankton biomass and composition off Oregon during cold and warm environmental regimes. We have identified a small subset of fish whose larvae can be monitored as indicators of warm and cold phases in the northeast Pacific Ocean. KEY WORDS: Larval fish · Density · Diversity · Temporal variability · Upwelling ecosystem · California CurrentResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 366: 187-202, 2008 provide information on the relative effects of climate and fishing on marine fish populations (Hsieh et al. 2005).Ichthyoplankton collections were made from sampling every 2 wk along the Newport Hydrographic (NH) line off Newport, Oregon from 1996 to 2005. This period witnessed dramatic and perhaps unprecedented change in climate, ocean dynamics, and biological communities (Peterson & Schwing 2003, Hooff & Peterson 2006. The timing of these ichthyoplankton collections coincided with a wide variety of environmental conditions (e.g. warm and cool climate regimes, El Niño and La Niña events, and extended periods of positive and negative upwelling). This makes these data particularly suitable and valuable for evaluating changes in ichthyoplankton abundance relative to a fluctuating environment. The NH line was sampled intensively in the 1970s and 1980s (Richardson & Pearcy 1977, Mundy 1984, Boehlert et al. 1985, Brodeur et al. 1985, Doyle et al. 1993, 2002, so substantial historical data exists during different oceanographic regimes with which to compare our data.The purposes of this study are to: (1) identify and compare larval fish concentration and community structure from samples collected at 2 nearshore stations off the central Oregon coast to test for annual, seasonal, and monthly differences; (2) compare and contrast these findings to those of similar historical studies along the NH line; and (3) relate the larval communities to fluctuating marine environmental conditions observed in this dynamic upwelling region. We assessed trends in larval concentrations and diversity indices u...

Winter ichthyoplankton biomass as a predictor of early summer prey fields and survival of juvenile salmon in the northern California Current

“…Doyle et al (2002) examined the spring and early summer ichthyoplankton assemblages in the NCC from Washington to northern California and found substantial latitudinal coherence in the species assemblages, with most of the spatial variability related to cross-shelf differences. Additionally, Auth (2008) found that the ichthyoplankton community between southern Oregon and central Washington (43.00-47.00°N) in May 2004-2006 was similar in terms of concentration, distribution, and community structure, while Auth (2011) also found no significant north-south concentration pattern for total larvae collected in May-October 2004-2009 between southcentral Oregon and southern Washington (44.00-46.67°N). Finally, the relationship between the larval community in this region and broad NCC basin-scale indices such as MEI, NOI, and PDO has been documented in several recent studies (Auth 2008, 2011, Brodeur et al 2008, Auth et al 2011.…”

“…This may have led to fewer larvae surviving or a shift in their distribution off the shelf, potentially rendering them unavailable to juvenile salmon as prey. This delayed upwelling negatively affected larval fish growth and survival as well as seabird breeding success (Sydeman et al 2006, Auth 2008, Takahashi et al 2012. El Niño years may also be character ized by reduced or ineffective upwelling that has been shown to result in dramatic changes in the ichthyoplankton communities in the NCC (Brodeur et al 1985, Doyle 1995, Lenarz et al 1995.…”

“…Re gimes defined as warm included the years 1998, 2003-2005, 2007, 2010; those defined as cold included 1999-2002, 2006, 2008, 2009. These designations followed upon those outlined in Brodeur et al (2008) and as indicated by positive (warm) and negative (cold) phases in the MEI and PDO.…”

“…Sampling was conducted primarily at night using either a 1 m diameter ring net with 333 µm mesh or a 60 cm diameter bongo net with 200 µm mesh (333 µm after 2005), as described in Brodeur et al (2008). Each net was fished as a double oblique tow within the upper ~20 m of the water column at a retrieval rate of ~30 m min −1 and a ship speed of 1.0 to 1.5 m s −1 .…”

“…While plankton samples collected along the NH line during May and June include species of fish larvae that are important prey for juvenile salmon during their early marine residence (Brodeur et al 2008), juvenile salmon do not typically eat fish larvae but instead consume larger juvenile stage fishes (Daly et al 2009). In the absence of direct sampling of the prey community important to juvenile salmon, we explored the ocean conditions and the larval fish community during winter and early spring, a time of peak larval fish abundance in the NCC (Brodeur et al 2008), which may function as a surrogate for the early summer juvenile fish prey field of salmon.…”