Stock assessment of the bluemouth (Helicolenus dactylopterus) in Azorean waters during the 1990-2002 period, applying a biomass dynamic model
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Bluemouth (Helicolenus dactylopterus), a benthic fish mostly inhabiting at depths between 500 m and 600 m, represents a highly valuable economic resource for local fishermen at the Azores Islands (NE Atlantic). Nominal catches of bluemouth increased from 1990 through 1994, and declined afterwards reaching in 1999 the lowest value recorded. Standardized catch per unit effort (CPUE) was used as an index for stock relative abundance; a General Linear Model, considering several factors that may have affected the fishing efficiency of commercial vessels, was run to obtain this CPUE index. These factors were: fleet type, year, month, and boat size; the last three factors were found to be statistically significant. A discrete version of the Schaefers Biomass Dynamic Model was applied to the bluemouth stock assessment and the model parameters were estimated using the standardised CPUE series for calibration. A risk analysis using Monte Carlo simulations was carried out to estimate the probability of the stock biomass at the beginning of 2003 to be below the stock biomass at the beginning of 2002, after a given catch was extracted. Assuming a precautionary approach and keeping in mind that this resource could be depleted (0.19< B2002 /Bopt <1.55, with a 95% probability), this analysis determined that catches for the year 2003 should not exceed 250 t, which correspond to a 10% probability of generating a biomass decline at the beginning of 2003. As an additional indicator of the state of the resource, the size distribution of bluemouth landings was analyzed complementary. This analysis showed a decrease of the mean length, mainly for catches coming from regions with the highest concentrations (depths greater than 300 m). Future annual monitoring efforts to estimate and diagnose the state of the bluemouth resource are highly recommended.