Bayesian Assessment of Northeast Atlantic Spurdog Using a Stock Production Model, with Prior for Intrinsic Population Growth Rate Set by Demographic Methods

Abstract

Schaefer-model stock assessments can be imprecise when they are fitted to catch rate data (CPUE) because a large, unproductive stock can often explain CPUE trends as well as a small, productive one. However, consideration of life-history characteristics can improve parameter estimates by constraining maximum productivity. Therefore, we applied the methods of McAllister et al. (2001) to Northeast Atlantic spurdog (Squalus acanthias) by using demographic techniques to convert prior distributions for age-specific fecundity and natural mortality (the latter based on published estimates from tagging studies) to prior distributions for the intrinsic rate of population growth (r). The priors for r generated in this manner were then used in a Bayesian, Schaefer-model assessment of spurdog, fitted to bottom trawl survey CPUE data. Results suggest the stock is depleted to about 5% of virgin biomass.

Spatio-temporal patterns in demersal elasmobranchs from trawl surveys in the eastern English Channel (1988–2008)

“…Finally, survey trends for M. asterias appear to be stable (Ellis et al 2005b), in coherence with the temporal trend presented here. Density data presented here for the benthopelagic Squalus acanthias are likely to reflect a combination of low occurrence in the area surveyed (which may also be a seasonal effect), low gear selectivity, and the fact that the stock is considered depleted (Hammond & Ellis 2005). Furthermore, trawl catches for this species may not be an adequate indicator of stock status given its tendency to aggregate (Pawson 1995, Fordham et al 2006.…”

Who let the dogfish out? A review of management and socio-economic aspects of spiny dogfish fisheries

“…Spiny dogfish (called spurdog in Europe) are the most commercially important shark species in the Northeast Atlantic, and this stock has been widely exploited (Hammond and Ellis 2005). Historical data on spiny dogfish landings have been collected by the International Council for the Exploration of the Sea (ICES) since the early 1900s, although they were included in the generic category of dogfish, for which other Squalidae (e.g., Squalus blainvillei), Triakidae (e.g., Mustelus spp., and Galeorhinus galeus) and Scyliorhinidae (e.g., Scyliorhinus canicula) shark species may have been included (Pawson et al 2009).…”

In search of climate effects on Atlantic Croaker (Micropogonias undulatus) stock off the U.S. Atlantic coast with Bayesian state-space biomass dynamic models

“…McAllister et al's (2001) Equations 9-14 or Hammond and Ellis' (2005) Equations 1-5 were applied as appropriate. During the sampling, there were negative values of r. These values usually result from generating stochastic reproductive rates and survivorship values independently of one another, including coupled low values of these parameters, the combination of which can lead to a population that cannot sustain itself (McAllister et al, 2001;Hammond and Ellis, 2005). The fi nal prior probability density function for r (Table 1) was developed after discarding those negative r values and ensuring that the age structure of the projected population was stable (population stability occurred since year-3).…”