A Bayesian stock assessment incorporating discards estimates in some years

• Main Authors: Fernández-Llana, C. (Carmen), Cerviño, S. (Santiago), Pérez-Contreras, M.N. (María Nélida), Jardim, E. (Ernesto)
• Format: Report
• Language: English
• Published: Centro Oceanográfico de Vigo 2008
• Subjects: Hake; North Atlantic; Northeast Atlantic
• Online Access: http://hdl.handle.net/10508/9062

We develop a Bayesian age-structured stock assessment model that takes into account the information available about discards and is able to handle gaps in the time series of discards estimates. The mechanism for doing this is to explicitly incorporate a term in the model reflecting mortality due to discarding, and to make appropriate assumptions about how this mortality may change over time. The result is a stock assessment that takes due account of discards while, at the same time, producing a complete time series of discards estimates. The method is applied to the hake stock in ICES divisions VIIIc and IXa, which experiences very high discarding on the younger ages. The stock is fished by Spain and Portugal, and for these countries there are only discards estimates in recent and non-coincident years. Two runs of the model are performed, one assuming zero discards and another one incorporating discards. Results are compared and discussed and possible implications for management briefly commented on.