Differential somatic growth rates and population subdivision of region separated by Point Conception, CA, in a depleted rockfish, cowcod (Sebastes Levis)

Cowcod rockfish (Sebastes levis), a once commonly harvested (commercially and recreationally) species within Californian waters, was declared overfished in 2000, and added to the National Marine Fisheries Service Species of Concern list in 2004. To assist in the conservation of this species, we used otolith microchemistry and microstructure to obtain information related to population structure and the spatial variability of juvenile somatic growth. We hypothesized that a location of large upwelling near Point Conception, CA may act as a dispersal barrier for cowcod rockfish, resulting in population structure (currently, fisheries managers assume a single continuous population).  If population structure is detected, we hypothesized that juvenile somatic growth rates would differ among populations owing to the different environments each population resides. To address these objectives we used archived collections of otoliths that were obtained throughout the species range. Using trace element concentrations from whole otoliths we identified two populations of cowcod rockfish that were separated at Point Conception. Further, based on otolith microstructural analyses we detected significant differences in juvenile somatic growth rates between these two populations. These results suggest that a management approach, which considers two populations with differential growth rates, may better assist the rebuilding of this species.