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

We examined ichthyoplankton sampled from 2 stations, 9 and 18 krn 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.