Synthesising sea bass recreational catches, length-frequencies, and post-release mortality for stock assessment: Working document for WKBSEABASS, 07 November 2024
Hyder, K.; Edwards, W.; Cardinale, M.; Catarino, R.; Chen, C.; Curtis, D.; Drogou, M.; Earl, T.; Lambert, G.; Lanssens, T.; Olesen, H.J.; Van de Pol, L.; Régimbart, A.; Roche, W.; Ryan, D.; Rudd, H.; Salvany, L.; Schuchert, P.; Selles, J.; Skov, C.; Strehlow, H.V.; Verleye, T.; Winter, A.-M.; Wögerbauer, C.; Woillez, M.; Vertegaal, D.; Weltersbach, M.S.; White, J.; Radford, Z. (2024). Synthesising sea bass recreational catches, length-frequencies, and post-release mortality for stock assessment: Working document for WKBSEABASS, 07 November 2024. ICES: Copenhagen. 41 pp.
Marine recreational fisheries catch of sea bass are an important part of the overall removals representing 27% of total removals in 2012, so need to be included in the stock assessment. This working document outlines the synthesis of sea bass recreational catches, length-frequencies, and post-release mortality, for use in the sea bass benchmark (WKBSEABASS) and inclusion in future stock assessments. There were many challenges in integrating national survey data across countries exploiting the stock (i.e., Belgium, Denmark, France, Germany, Ireland, the Netherlands, and the UK). The surveys covered both retained and released catches, as well as length-frequency data. National surveys had different coverage, methodology, and temporal resolution which made creating a comprehensive time series challenging. In addition, management measures have been implemented and changed regularly, making constructing time series of the retained and released component more difficult. This meant that it was important to generate not just catches, but also the associated uncertainty and biases.Kept and released estimates and associated errors were combined for each modelling scenario and area accounting for missing errors, countries, years, and partitioning between areas. An assessment of the level of bias in each survey was combined to provide an overall assessment of bias that indicated that bias was negative before 2015 and positive for 2016. An approach for assessing the impact of management measures provided forward projections of the levels of catches. Forward projections overestimated the impact of management measures with the difference largest for the released component. Seasonality in raw catches showed highest catches in summer and lowest in winter. A similar approach was used to reconstruct length-frequencies, but only provided before and after the implementation of management measures. Limited studies of post-release mortality exist, with the most robust estimate of 5.0% [1.7, 14.4%]. It is important that the uncertainties in the estimates are used to inform a broad sensitivity analysis to understand the impact on outcomes from the assessment. The analysis done represents a step change towards synthesising marine recreational fisheries data from diverse sources and understanding the issues, uncertainties, and biases. However, a consistent time series and robust uncertainty analyses are needed, so continued refinement of the approach should be done as more survey data is generated.
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