Terrestrial and marine correlates to black rockfish (Sebastes melanops) growth in the California and Alaska Coastal Currents

Nearshore productivity is influenced by terrestrial and marine inputs, with some regions influenced more heavily by one input source rather than the other.  Productivity in the California Current has been closely related to marine indices, but in the Alaska Coastal Current, terrestrial inputs from rivers and glaciers may also play a role.  Annual growth records in otoliths can provide an opportunity to compare the relative influence of marine and terrestrial sources on fish productivity across both currents.  We examined black rockfish otoliths from the California Current (Arcata/Eureka, CA; collected by NOAA) and the Alaska Coastal Current (Sitka, AK; collected by Alaska Department of Fish and Game and USGS).    Otoliths were thin-sectioned, photographed, and visually cross-dated.  Annual increment widths were then measured and the cross-dating was statistically verified.  Next, each measurement time series (individual fish) was detrended, to remove age-related variation, and averaged to generate a growth chronology.  Growth chronologies were compared with monthly values of sea surface temperature, upwelling, the Pacific Decadal Oscillation (PDO), and the Northern Oscillation Index (NOI), as indices of marine influence and river discharge as an index of terrestrial influence.  For the California Current, otoliths provided a growth chronology that spanned several decades (1967–1984 and 1989-2006). The growth chronology was positively correlated with upwelling (r = 0.48 – 0.49) and the NOI (r = 0.30 – 0.71) and negatively correlated with the PDO (r = 0.42 – 0.45) and SST (r = 0.40 – 0.57) during winter months.  Klamath River discharge was negatively correlated with growth in September (r = 0.31).  The Alaska Coastal Current chronology also spanned several decades (1975-2008).  Fish growth in Alaska was also negatively correlated with autumn discharge in November and December (r = 0.42-0.52), but growth was positively correlated with summer SST (r = 0.33- 0.45) and relaxed spring downwelling (r = 0.51). At present our results reflect differences in the oceanography of the two current systems and collections from additional sites are currently under preparation.