Research Document - 2015/065

Framework Assessment and 2013 Update using a Stage-based Population Model for Spiny Dogfish (Squalus acanthias) in the Northwest Atlantic

By G.M. Fowler and S.E. Campana

Abstract

A stage-based migration model of population dynamics, with abundances aggregated into region, season, sex and maturity stages, was developed to represent the transboundary (US and Canada) population of dogfish occurring throughout waters of the Gulf of Maine, Bay of Fundy, and Scotian Shelf. The model also facilitates estimation of independent stock abundance models by region, by disabling migration parameters, but this was found to under-estimate stock abundance in Canadian waters. Simulation studies with the model were used to investigate reference point candidates for gauging stock status. Adult female abundance (SSN) and exploitation (Fssnmsy) stood out as the most critical aspects of the population to monitor. Projections of various exploitation scenarios were used to estimate consequences of harvest strategies relative to these reference points.

The framework model terminated in 2010, as there is no detailed length composition data for US catch and survey sampling in more recent years. Several approaches to update stock status to 2013 were investigated. The option chosen was to treat available summary estimates of US catch and population biomass as relative adjustments to those of earlier years. Assumptions about size compositions, especially those of the commercial catch, were required to accomplish this. The population had been declining from 1992 to 2007, possibly having exceeded its carrying capacity as fisheries could not account for the drop. Since 2007, the population has been growing, and in 2013, was estimated to be 789.2 million. This is 95.5% of the assumed abundance at maximum sustainable yield (Amsy) of 819.7 million. The carrying capacity is currently assumed to be the maximum estimated population size seen in the historical time series.

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