The Northern California Current (NCC) ecosystem is part of the North Pacific eastern boundary marine ecosystem and as such is dominated by interannual and seasonal variability in relation to larger scale atmospheric and surface current circulation patterns. There is a limited understanding of how climate- and seasonal-related changes will affect pelagic nekton diversity and distribution ranges in the NCC ecosystem. Here we examined the spatial and temporal trends in pelagic fish and invertebrate species distributions, community structure and biodiversity with respect to regional and local oceanographic conditions off the Oregon and Washington coasts. Pelagic species were sampled from 1998 to 2011 in surface trawl surveys conducted tri-annually at on average 52 stations located along 11 transects during the spring-summer months from 44°N to 48°N. Abundance data (individuals per km towed) were collected for a total of 105 taxa of fish and invertebrates sampled by the trawls.
Results/Conclusions
Based on ordinations, multi-response permutation procedure (MRPP) and indicator species analysis (ISA), the yearly-scale species assemblages were structured primarily by distance from shore and sea surface temperature. Sea nettle jellyfish, juvenile Chinook salmon, and Pacific herring species dominated the nearshore community (stations ≤ 8 km from shore), mid-shelf (stations >8-24 km) communities were characterized by juvenile coho salmon, Pacific sardine, and California market squid and the off-shore (stations > 24 km) community was characterized by Pacific saury, juvenile steelhead and chum salmon. ISA and MRPP also indicated that there was a latitudinal gradient in species assemblages such that south of Cape Meares, OR the community was dominated by two jellyfish species (water jelly and moon jelly) and by the ocean sunfish and the northern community (north of Grays Harbor, WA) was described by three salmonid species (coho, chum, and sockeye) as well as Pacific herring and spiny dogfish. Total species richness was in general higher than average from 2002-2010 (with some exceptions) and lower than average between 1998-2001. The Shannon-Wiener and Simpson’s Diversity Indices varied substantially from year to year with highest diversity occurring in 2000 and lowest in 2007. We also present the spatial distribution of some non-salmonid indicator species such as forage fish (herring, sardine and anchovy), Pacific saury and California market squid. The results from our study suggest that pelagic nekton communities are dynamic within the NCC on interannual time scales.