Biomass and Harvest Rates for Coastal Newfoundland and Labrador Snow Crab during 1990-2012

Snow crab (Chionoecetes opilio) fisheries are economically very important in Newfoundland and Labrador, contributing 33% to the provincial total landed value in 2013. This fishery has recently been MSC certified with requirements for reference points and harvest control rules. The main objective of this study was to estimate stock biomass and harvest rates to better understand population dynamics and to provide inputs to future harvest control rules. A depletion model was developed for catch-per-unit-effort (CPUE) data for 5 spatial fishing zones during 1990-2012. This model included a random walk in CPUE catchability over years and within fishing regions, to reduce confounding between CPUE catchability and the biomass level. The model was implemented using ADMB. The fit of the model was better after 2000 because of higher levels of effort and depletion in this period. This resulted in tighter confidence intervals for stock biomass after 2000. Results indicate that stock biomass has declined over time for all regions combined, and that harvest rates have increased and are higher in NAFO Divisions 2HJ3K than in 3LNO. Assumptions of the model were examined closely using a variety of diagnostic analyses.