| Abstract: |
The abundance of yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) was sampled concurrently with physical (temperature, salinity, water depth) and biological variables (chlorophyll a concentration and copepod abundance) along Washington and Oregon coast in June 1998–2006. Copepods were divided into four different groups by their water-type affinities: cold neritic, subarctic, warm neritic and warm oceanic, and each group was used an independent environmental variable. Data collected in 1998 – 2008 were used to perform nonparametric correlation and negative binomial loglinear mixed regression with a spatial random factor, and data collected in 2006 was used to validate the models. Yearling Chinook abundance was negatively related with temperature, and positively related to the density of cold neritic copepod, chlorophyll a concentration, and salinity. Yearling coho abundance was positively related with temperature, and negatively related with warm oceanic copepods, warm neritic copepods, and water depth. The two salmon species also showed different spatial patterns in most years. Yearling Chinook abundance showed significant spatial autocorrelations in 1999, 2000, 2002, 2004, and 2005, and yearling coho abundance showed significant spatial autocorrelations in 2000 – 2002. The spatial random factor in the negative binomial loglinear mixed model was positively correlated with juvenile salmon abundance and showed similar spatial cluster patterns as juvenile salmon abundance for both species. Thus the occurrence of spatial autocorrelation could be attributed to the spatial random. Both annual mean abundance of yearling Chinook and the spring Chinook jack counts, a measurement of local population success, were positively correlated with cold neritic copepods. The annual mean abundance of yearling coho and the ocean survival rate were negatively correlated with warm oceanic copepods. The differences in how each species mapped onto habitat variable might be explained by the fact that yearling coho has relatively wider coastal distribution, and could feed on a relatively wider range of prey items than yearling Chinook. To address the spatial autocorrelation and the difference between two species, information on other physical processes, such as large scale transports, eddies and fronts, and biological processes such as prey and predator may be necessary. |
