Applying length-based assessment methods to fishery resources of the Bay of Biscay and Iberian Coast ecoregion: stock status and parameter sensitivity

Poster.-- XVII International Symposium on Oceanography of the Bay of Biscay, 1 – 4 June 2021, Virtual EventLength-based methods have been widely applied to estimate biological parameters and to understand the dynamics of marine resource populations within the category of data-limited stocks. However, few studies have been performed to date to test the parameter sensitivity of length-based methods on stocks with different traits and fishery contexts. In the Bay of Biscay and the Iberian Coast ecoregion, SE Europe (ICES, International Council for the Exploration of the Sea, Divisions 8 and 9a), many commercial resources are considered data-limited and little is known about their stock status or some issues in their current assessment remain open. Therefore, this study focuses on two of the most used length-based methods suggested by ICES as the most appropriate to evaluate data-limited stocks, namely length-based indicators (LBI) and length-based spawning potential ratio (LBSPR). Both methods have been applied to assess the stock status of a number of relevant species in the study area, such as: the small-spotted catshark (Scyliorhinus canicula), European anchovy (Engraulis encrasicolus), blackspot seabream (Pagellus bogaraveo), pouting (Trisopterus luscus), pollack (Pollachius pollachius) and Norway lobster (Nephrops norvegicus). For each stock, model results have been compared with available knowledge of their current status. Furthermore, we discuss if unexpected results can be related to violations of the main model assumptions (constant total mortality and recruitment, and logistic selectivity) or to the non-representativeness of stock length composition. In addition, a sensitivity analysis has been conducted of the two most important input parameters: L∞ (von Bertalanffy asymptotic average maximum body size) and M/k (ratio of natural mortality to von Bertalanffy growth rate). This analysis concludes that the variation/misspecification of both parameters (M/k and L∞) has a considerable impact on the results given by both methods, and that this effect is more significant in the case of the L∞ parameter, thus highlighting the importance of its accuracy in assessmentN