A length-based multispecies model for evaluating community responses to fishing

Abstract

Quantitative ecosystem indicators are needed to fulfill the mandate for ecosystem-based fisheries management. A variety of community metrics could potentially be used, but before reference levels for such indices can be established the sensitivity of candidate indices to fishing and other disturbances must be determined. One approach for obtaining such information is to test candidate indicators with models that mimic real ecosystems and can be manipulated experimentally. Here we construct a size-based multispecies model of a community of fish species that interact by predation. The model was parameterized for 21 fish species to obtain a predation-regulated community. Following an analysis of the sensitivity of the model to parameter uncertainty, we tested the sensitivity of community-level indicators to increasing levels of fishing mortality (F). Abundance and biomass spectra were sensitive to fishing mortality, with the slope decreasing with increasing F. Species diversity size spectra were also very sensitive to F, with diversity in the largest size classes declining rapidly. In contrast, k-dominance curves were less sensitive to fishing pressure. Importantly, however, although most community-level metrics showed clear trends in response to fishing, single-species declines in spawning stock biomass were the most sensitive indicators of fishing effects

Reconciling end-to-end and population concepts for marine ecosystems

“…ATLANTIS has hundreds of parameters (see Plaganyi (2007) There has been a revival of interest in size-based portrayals of prey-predator relations as an alternative to food web structure within fish communities (Hall et al 2006;Pope et al 2006). These have the advantage of simulating virtual "species", defined by initial and final lengths and length at maturity, without requiring specific names.…”

“…To illustrate this similarity, we compare percentage abundance in terms of three fish size categories (small, medium and large) in the Georges Bank ecosystem (Fig. 4a) derived from the asymptotic lengths of the 21 species used in Hall et al (2006), with the relative abundances expressed in terms of 35 species allocated to feeding guilds (Fig. 4b).…”

Rebuilding Global Fisheries

“…They range from simpler community models to more-complex ecosystem models (12). Figure 2 displays equilibrium solutions from a size-based community model, which assumes that fishing pressure is spread across species according to their size and that a subset of species remains unfished (13). Results of more-complex ecosystem models across 31 ecosystems and a range of different fishing scenarios were remarkably similar ( fig.…”

When is a fishery sustainable?

“…The most widely used is Ecopath with Ecosim (EwE) (Pauly et al 2000), followed by Atlantis (Fulton et al 2011a), but numerous other models have also been used or proposed (e.g., Hall et al 2006;Matsuda and Abrams 2006;Travers et al 2010;Blanchard et al 2014;Jacobsen et al 2014).…”