Author: Marta  Cousido-Rocha,   (Instituto Español de Oceanografía)

Designation: 

Description:
Length-based methods have been widely applied to estimate biological parameters and to understand the dynamics of marine resources populations under the category of data-limited stocks. However, there are still few studies testing sensitivity of parameters of length-based methods on stocks with different traits and fisheries contexts. In the Bay of Biscay and Atlantic Coast ecoregion , SE Europe (ICES, International Council for the Exploration of the Sea, Area 8 and Division 9a), many commercial resources are considered data-poor and little is known about their stock status. Therefore, in this study we focuses on two of the most used length-based methods that were suggested by ICES as the most appropriate to evaluate data-poor stocks, which are  the length-based indicators (LBI) and the length-based spawning potential ratio (LBSPR). We applied both methods 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, we compared model results with previous knowledge of their status. Furthermore, we have also analysed if unexpected results can be related to some violations of the main model assumptions (constant total mortality and recruitment, and  logistic selectivity) or not representativity of length stock composition. Both approaches, LBI and LBSPR, are highly sensitive to assumptions about biological information. Therefore, secondly, we run a sensitivity analysis 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).  Such analysis concludes that the variation/misspecification of both parameters (M/k and L∞) has a strong effect on both method results, and that such effect is more significant in the case of the L∞ parameter, highlighting the importance of its accuracy in the assessment.

Category: Scientific Program Abstract > Special Sessions > CS22 Fish and fisheries