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Incorporating environmental variability in stock assessment: predicting recruitment, spawner biomass, and landings of sprat (Sprattus sprattus) in the Baltic Sea

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Abstract:

Temperature has a significant positive impact on recruitment of sprat, Sprattus sprattus, in the Baltic Sea. Here we evaluate whether an existing recruitment model for the year classes 1973–1999 can forecast recruitment for five new year classes. The coefficient of variation (CV) of predictions was 5%, and four of five new year classes were within 95% confidence limits of predictions made by the earlier model. We then assimilated climatic, oceanographic, and recruitment linkages and their uncertainty into the standard International Council for the Exploration of the Sea (ICES) assessment procedure to predict key advisory-related variables such as spawning stock biomass (SSB) and landings. These linkages enable a forecast of recruitment earlier than the annual assessment meeting. Forecasts made using the North Atlantic Oscillation to predict the 2006year class showed that spawner biomass would be 15% lower than spawner biomass calculated using the ICES standard methodology. The difference in perception of future biomass does not affect the advice for the stock because the spawning stock biomass is greater than the critical biomass limit (SSB> BPA). However, when this is not the case or when it is desirable to broaden the ecosystem basis for fisheries management, incorporation of knowledge of recruitment processes may be beneficial.

La température a un effet positif significatif sur le recrutement du sprat, Sprattus sprattus, dans la Baltique. Nous vérifions ici si un modèle préexistant du recrutement des classes d’âge de 1973–1999 peut prédire le recrutement pour cinq nouvelles classes d’âge subséquentes. Le coefficient de variation (CV) des prédictions est de 5 % et quatre des cinq nouvelles classes d’âge se situent dans l’intervalle de confiance de 95 % des prédictions du modèle antérieur. Nous incorporons ensuite les liens climat–océan–recrutement et leur incertitude dans la procédure courante d’évaluation du Conseil international pour l’exploration de la mer (CIEM, « ICES ») pour prédire les principales variables, telles que la biomasse du stock reproducteur (SSB) et les débarquements, qui servent à émettre des avis. Ces liens permettent de faire une prédiction du recrutement avant la tenue de la réunion annuelle d’évaluation. Les prédictions faites à l’aide de l’oscillation nord-atlantique concernant la classe d’âge de 2006 ont montré que la biomasse des reproducteurs serait de 15 % inférieure à la biomasse des reproducteurs calculée par la méthodologie standard de l’ICES. La différence de prévision de la biomasse future n’affecte pas les avis émis concernant le stock, car SSB > BPA. Cependant, lorsque ce n’est pas le cas, ou lorsqu’il est souhaitable d’élargir la base écosystémique pour des fins d’aménagement de la pêche, l’incorporation de la connaissance des processus de recrutement peut être bénéfique.

Document Type: Research Article

Publication date: 2008-07-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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