A length-structured spatially explicit model for estimating hake growth and migration rates

Drouineau, H., Mahévas, S., Bertignac, M., and Duplisea, D. 2010. A length-structured spatially explicit model for estimating hake growth and migration rates. – ICES Journal of Marine Science, 67: 1697–1709. Despite an abundant literature, hake growth and migration remain poorly understood. A recent tagging campaign and an analysis of the growth increments on juvenile hake otoliths demonstrate that the growth rate has probably been largely underestimated. Migration rates have been studied through qualitative analysis of catch rate, but have not been confirmed by a more-quantitative analysis. Those biological uncertainties affect stock assessments and predictions by the uncertainty they bring to age–length keys and by hindering our ability to assess the impact of spatial management measures. Here, a spatially explicit length-structured model is developed to improve the biological knowledge of European hake (Merluccius merluccius), in terms specifically of migration and growth. The model belongs to the state–space class of models and is fitted by maximum likelihood on commercial landings, survey abundance indices, and tagging data. The estimated growth curve is close to estimates from tagging data, lending weight to the assumption of the species being fast-growing. Few migrations are long in distance, and there are none between the Bay of Biscay and the Celtic Sea. The model also demonstrates a high level of heterogeneity in the spatial distribution of spawning-stock biomass, with concentrations on the margins of the continental shelf.