Growth variability in the splitnose rockfish Sebastes diploproa of the northeast Pacific Ocean: pattern revisited

Understanding patterns of somatic growth within populations greatly contributes to fisheries stock assessment. Splitnose rockfish Sebastes diploproa was reported as having a striking pattern of latitudinal growth variability from studies conducted in the 1980s. We investigated variation in growth parameters of splitnose rockfish by latitude using recent data from the NOAA Fisheries Groundfish Survey (2003- 2008), current ageing techniques, and advanced modeling and statistical methods to provide an updated understanding of growth along this species' latitudinal range. Sex- specific age data were fit to a von Bertalanffy growth function incorporating ageing error, and growth parameters were estimated for 5 areas along the U. S. west coast, specified based on biogeographic boundaries. Resampled values of each growth parameter were then fit to linear models, and Akaike's information criterion (AIC) was used to evaluate hypotheses for growth parameter relationship with latitude. We found that splitnose rockfish exhibited a cline in asymptotic length (L-infinity), with L-infinity increasing with rising latitude. We also found that although the growth coefficient (k) was smallest in the most southern area, there was no apparent cline along the coast; a northward cline in k has previously been reported in the literature. We propose that differences in fishing intensity could be responsible for the cline in L-infinity, as higher fishing pressure in the south could skew the size distribution of the population in that region and reduce southern L-infinity estimates. We also attribute slower growth in the southern area to oceanographic characteristics and low productivity of the area south of Point Conception.