Publication Abstract

A stock assessment model for Northeast Atlantic spurdog, incorporating fecundity data to estimate the extent of density dependence in pup production

A stock assessment model for Northeast Atlantic spurdog, incorporating fecundity data to estimate the extent of density dependence in pup production

J.A.A. De Oliveira*, J.R. Ellis* and H. Dobby

A stock assessment model for Northeast Atlantic spurdog (Squalus acanthias) is presented. The model is based on an approach developed for tope (Galeorhinus galeus) off southern Australia. It is essentially age- and sex-structured, but is based on processes that are length-based, including maturity, pup-production, growth and gear selectivity, with a length at age relationship used to convert length to age. Pup-production (recruitment) is closely linked to the numbers of pregnant females, but the model allows deviations from this relationship to be estimated (subject to a constraint on the amount of deviation), and parameter estimates to be based on fitting fecundity data. The model fits to a combined Scottish groundfish survey index of abundance, and to proportion-by-length-category data from both the survey and commercial catches (aggregated across gears). The only estimable parameters considered are the number of pregnant females in the virgin population, selectivity-by-length-category for Scottish surveys (4 parameters) and two commercial fleets (3 parameters each), the extent of density dependence in pup-production, and constrained recruitment deviations (1960–2009). The model is taken back to 1905 to better reflect virgin conditions and to allow early fecundity data to be fitted in order to estimate the extent of density dependence in pup production. The model estimates 2010 population levels to be about 18% relative to 1905, and 22% relative to 1955.

J.A.A. De Oliveira*, J.R. Ellis* and H. Dobby

ICES Annual Science Conference 2010, Nantes. ICES CM 2010/E:20: 33pp