Estimating growth from sex ratio-at-length data in species with sexual size dimorphism

Individual growth is one of the main processes which drive the population dynamic and stock productivity. Many fish have differential individual growth by sex. Growth is affected by sexual development, which is frequently reached at different sizes in males and females. Differences in growth per sex after maturity produce different patterns in sex proportions-at-length in the population. If these patterns are the consequence of changes in life history parameters, sex ratio-at-length data can be expected to contain significant information on the population life history. In this paper I first explore how post-maturity changes in life history may shape these patterns in sex ratio-at-length; secondly I explore how these data may be used to estimate growth parameters and finally I discuss how this information may be useful for stock assessment purposes. I use European hake data and life history parameters to model expected sex ratios. The results suggest that reproductive energy allocation leads to a lower growth rate in male hakes than in females. Moreover the sex ratio-at-length may provide useful information for estimating growth parameters in dimorphic species if additional information from other sources is available. Finally, these data can easily be factored into stock assessment models to help provide a better estimation of growth parameters and mortality rates. This valuable, accurate and cheap biological information (sex ratio-at-length) may play an important role in population dynamic models and stock assessment for species with sexual size dimorphism.Preprint

La experiencia europea en recuperación de stocks sobreexplotados ¿Qué hemos aprendido del plan de recuperación de merluza?

La sobrepesca es uno de los principales problemas que tienen que abordar los organismos gestores de las pesquerías si pretenden obtener de éstas el máximo rendimiento sostenible. Cuando la sobrepesca se mantiene en el tiempo, la respuesta esperable por parte de las poblaciones explotadas es una reducción de su capacidad reproductiva de tal manera que su recuperación se hace difícil y se alarga en el tiempo con importantes consecuencias económicas y sociales. Es entonces cuando los planes de recuperación son necesarios. Los planes de recuperación surgen en Europa como un caso especial de los planes de gestión plurianuales, donde el principal objetivo es recuperar la capacidad reproductiva de stocks sobreexplotados. Estos instrumentos han sido inicialmente promovidos por la ONU a través de distintos acuerdos y han sido trasladados por los organismos gestores a sus normas legales. En Europa la principal norma es la Política Pesquera Común (PPC). La PPC pretende garantizar que la actividad pesquera sea sostenible desde el punto de vista medioambiental, económico y social. Para ello ha desarrollado diferentes ámbitos, uno de los cuales son los planes plurianuales. En este trabajo se pretende dar a conocer a la comunidad científica de la CTMFM la manera como la Unión Europea ha gestionado la recuperación de stocks sobreexplotados mediante sus planes plurianuales. La merluza fue uno de los primeros stocks identificados como sobreexplotados que se gestionó mediante un plan de recuperación. En 2004 se empezó a trabajar en ese plan que fue finalmente implementado en 2006. Ya han pasado 8 años lo que lo convierten en un buen ejemplo donde revisar los procesos del plan: la elaboración, el seguimiento y sus resultados. Como en todas las acciones de gestión donde la incertidumbre es un elemento ineludible ha habido aciertos y errores. Aprender de ambos es la mejor lección podemos sacar de esta experiencia.CTMFMVersión del editor0,000

An Applied Framework for Incorporating Multiple Sources of Uncertainty in Fisheries Stock Assessments

Estimating fish stock status is very challenging given the many sources and high levels of uncertainty surrounding the biological processes (e.g. natural variability in the demographic rates), model selection (e.g. choosing growth or stock assessment models) and parameter estimation. Incorporating multiple sources of uncertainty in a stock assessment allows advice to better account for the risks associated with proposed management options, pro- moting decisions that are more robust to such uncertainty. However, a typical assessment only reports the model fit and variance of estimated parameters, thereby underreporting the overall uncertainty. Additionally, although multiple candidate models may be considered, only one is selected as the ‘best’ result, effectively rejecting the plausible assumptions behind the other models. We present an applied framework to integrate multiple sources of uncertainty in the stock assessment process. The first step is the generation and condition- ing of a suite of stock assessment models that contain different assumptions about the stock and the fishery. The second step is the estimation of parameters, including fitting of the stock assessment models. The final step integrates across all of the results to reconcile the multi-model outcome. The framework is flexible enough to be tailored to particular stocks and fisheries and can draw on information from multiple sources to implement a broad variety of assumptions, making it applicable to stocks with varying levels of data avail- ability The Iberian hake stock in International Council for the Exploration of the Sea (ICES) Divisions VIIIc and IXa is used to demonstrate the framework, starting from length-based stock and indices data. Process and model uncertainty are considered through the growth, natural mortality, fishing mortality, survey catchability and stock-recruitment relationship. Estimation uncertainty is included as part of the fitting process. Simple model averaging is used to integrate across the results and produce a single assessment that considers the multiple sources of uncertainty.Versión del edito

A preliminary gadget model to assess the Spanish Red seabream fishery of the Strait of Gibraltar

This work shows the first implementation of gadget (an age-length based model) to the Spanish Red seabream fishery data from the Strait of Gibraltar: gadget is a toolbox developed to implement marine ecosystem models considering the fishing effect. Our goal is to launch a new approach for the Red seabream fishery assessment following Icelandic deepwater stocks example. Sooner or later, we would like to change the current category of this deep water fishery: from data poor to stocks with quantitative assessments. These trials should be attempted before planning a future Benchmark Grou

TENTH WORKSHOP ON THE DEVELOPMENT OF QUANTITATIVE ASSESSMENT METHODOLOGIES BASED ON LIFE-HISTORY TRAITS, EXPLOITATION CHARACTERISTICS, AND OTHER RELEVANT PARAMETERS FOR DATA-LIMITED STOCKS (WKLIFE X)

The Workshop on the Development of Quantitative Assessment Methodologies based on Life history traits, exploitation characteristics, and other relevant parameters for data-limited stocks (WKLIFE X), chaired by Carl O'Brien (UK) and Manuela Azevedo (Portugal) met virtually 5–9 October 2020, to further develop methods for stock assessment and catch advice for stocks in Categories 3 and 4, focusing on the provision of sound advice rules that are within the ICES MSY framework. This tenth workshop was convened to further address the challenges to the evidence base for the provision of ICES advice with specific reference to data-limited stocks. There is an increasing number of fish stocks in Categories 3 and 4 for which assessment of status relative to MSY proxy reference points is available but for which short-term forecasts and MSY-based ad vice are not available. For assessments using the stochastic surplus production model in contin uous time (SPiCT), WKLIFE X developed and evaluated ‘fractile rules’ that account for uncer tainty and allow to consider any percentile and demonstrated that ‘fractile rules’ are more effec tive and precautionary than the median rule (50th percentile) and the ‘2-over-3’ rule. Additional work on advice rules for stocks in Category 3 based on life-history traits (k), tested through sim ulation and management strategy evaluation (MSE), showed that the addition of specific multi pliers based on the stock’s life-history characteristics decreases the risk of the control rule´s per formance. Annex 3 to this report contains the revised technical guidance on methods and advice rules for stocks in Category 3. The revision of the accumulated decade of ICES documentation on methods and advice for data-limited stocks into a stand-alone technical guidance document requires significant effort and dedicated work beyond the time available at the WKLIFE X meet ing. It is proposed that a dedicated workshop be established to undertake and complete the up dating and revision into a single reference documentICES, U

Report of the Working Group for the Bay of Biscay and the Iberian Waters Ecoregion (WGBIE)

Informe sobre la evaluación de los stocks demersales del área del Golfo de Vizcaya y Aguas Ibéricas (Merluza, Rapes, gallos, cigalas, lenguado