Incorporating density dependence in pup production in a stock assessment of NE Atlantic spurdog Squalus acanthias

An age- and sex-structured stock assessment model for Northeast Atlantic spurdog Squalus acanthias is presented that includes length-based processes, such as maturation, pup production, growth, and gear selectivity, with a length-at-age relationship to convert length to age. It relates pup production functionally to numbers of pregnant females, allowing for density-dependent effects. Themodel was fitted to a combined Scottish groundfish survey biomass index, to proportion-by-length category data from both trawl surveys and commercial catch sampling from target and non-target fisheries, and to fecundity data. Themodel was run from1905 to better reflect virgin conditions and to allowearly fecundity data tobefitted inorder to estimate the extentof density dependence inpupproduction. Themodel estimated 2010 population levels to be about 23 % relative to 1955 and 19 % relative to 1905. Results confirm that the stock is depleted, but not to the extent estimated in a previous assessment. Current estimates of depletion would support an IUCN listing of “Endangered”, but not “Critically Endangered”. Model projections showed that a TAC of 1422 t (the last non-zero TAC) would allow future population growth