Comparing fishery-independent and fishery-dependent data to characterize West Coast groundfish populations

ABSTRACT Objective Fisheries-independent data from the California Collaborative Fisheries Research Program (CCFRP), a long-term marine protected area (MPA) and fishery monitoring study, have been incorporated as a data source into stock assessments of U.S. West Coast rockfish Sebastes spp. conducted in the past 5 years. We investigate the specific population information that is being gained from this fisheries-independent data source as compared to fisheries-dependent onboard observer data for three representative rockfish species. Methods We used length distributions and abundance indices for Blue Rockfish S. mystinus, Vermilion Rockfish S. miniatus, and Gopher Rockfish S. carnatus to characterize the differences in the information provided by each data source. We evaluated what new population information was being gained by using data from inside MPAs, whether an objectively designed fisheries-independent sampling method gathered different information about a population than a fisheries-dependent method, and whether the data could be applied to the population across the breadth of the species’ depth distribution. Results We found that the information to be gained from fisheries-independent data is species dependent. Gopher Rockfish exhibited similar size structure and trends in abundance, showing high congruency between CCFRP (fisheries-independent) and Observer Program (fisheries-dependent) data. In contrast, Vermilion and Blue rockfishes demonstrated differing trends between MPAs and areas open to recreational fishing and between sampling methods, indicating that CCFRP data are introducing information about juveniles and small adults of both species in nearshore waters and large adult Vermilion Rockfish from inside MPAs. Conclusions Our results demonstrate that the information gained from fisheries-independent data sources and data from inside MPAs is species specific and may augment fisheries-dependent data sets. Understanding the specific information that different data sources bring to analyses for different species assists with the development of uses and best practices for data in management analyses, leading to better informed management and thus conservation of nearshore rockfish populations.