Project
Turbot stock assessment enhancement
Turbot and brill are important commercial catch species in Netherlands. Unfortunately, the current scientific surveys used (SNS, BTS) in the performed assessment are poorly suited to track these large flatfish. Two approaches were proposed to solve this issue. One method has been to use an additional LPUE (landings per unit effort) index as a surrogate for stock biomass. This resulted with the LPUE index essentially driving the assessment as the dominant index used. However, in recent years, the reduced fishing efforts and area coverage has questioned its role as an unbiased indicator, thus it may be more closely related to the catches and the actual stock status remains uncertain. To help developing a better index for turbot/brill assessments an industry survey (BSAS) was statistically designed and has been conducted annually since 2018 with the aim to provide improved biological information for stock assessments. The data collection of BSAS was founded by EMFF/EFMZV. The design and implementation of the BSAS has been reviewed annually by WGNSSK, and in 2023 a project Data Arme Visbestanden (DAV) was initialized aiming to explore the method in generating biomass or age based indices for assessment.
In recent years, within the assessment working group, questions have been raised about the quality of the turbot assessment using LPUE indices, as well as the quality and feasibility of including BSAS in the assessment. With the upcoming turbot benchmark, it is crucial to investigate these aspects. Both LPUE indices and BSAS were originally designed for Brill as well and currently they are excluded in the brill North Sea assessment after the benchmark (WKBMSYSPiCT2) in 2022. Although in this project we focus on turbot, the analysis applies to brill as well. The evaluated survey quality of brill will be delivered to the brill stock coordinator for the future assessment of brill.
Tarbot is een belangrijke commerciële soort in de Noordzee. Binnen de beoordelingswerkgroep zijn de afgelopen jaren vragen gerezen over de kwaliteit van de tarbotbeoordeling met behulp van LPUE-indices, evenals over de kwaliteit en haalbaarheid van het meenemen van brancheonderzoek (BSAS) in de beoordeling. Met de komende tarbotbenchmark is het van cruciaal belang om de potentiële rol van deze twee indices in de beoordeling te onderzoeken. Het is nog niet gebruikelijk in de aandelenbeoordelingsgemeenschap om door de industrie zelf verzamelde gegevens als aandelenindices te gebruiken. De nieuwigheid van een dergelijke methode zal meer inzicht geven in het gebruik van goed ontworpen bedrijfsonderzoek bij de beoordeling van de bestanden en zal de samenwerking tussen industrie en wetenschap bevorderen.