Assessing the sensitivity and specificity of fish community indicators to management action

Abstract

We assessed ten trophodynamic indicators of ecosystem status for their sensitivity and specificity to fishing management using a size-resolved multispecies fish community model. The responses of indicators to fishing depended on effort and the size selectivity (sigmoid or Gaussian) of fishing mortality. The highest specificity against sigmoid (trawl-like) size selection was seen from inverse fishing pressure and the large fish indicator, but for Gaussian size selection, the large species indicator was most specific. Biomass, mean trophic level of the community and of the catch, and fishing in balance had the lowest specificity against both size selectivities. Length-based indicators weighted by biomass, rather than abundance, were more sensitive and specific to fishing pressure. Most indicators showed a greater response to sigmoid than Gaussian size selection. Indicators were generally more sensitive at low levels of effort because of nonlinear sensitivity in trophic cascades to fishing mortality. No single indicator emerged as superior in all respects, so given available data, multiple complementary indicators are recommended for community monitoring in the ecosystem approach to fisheries management.

Uses of Innovative Modeling Tools within the Implementation of the Marine Strategy Framework Directive

“…Thus, at the beginning of each cycle, a review of the indicator set and a model based study to select the most appropriate indicators in relation to pressures (Houle et al, 2012) would be prudent along with the evaluation of their scientific standard and applicability (Queirós et al, 2016a). Once an assessment of state for GES has been made, the next question likely to be faced by mangers is: are we moving in the right direction to maintain or recover GES?…”

“…Some of these criteria, such as the quantification of pressure-response relationships, can be evaluated using models. For example, indicators addressing disturbance of marine fish community structure through exploitation (i.e., fishing, a physical pressure) have been investigated (Houle et al, 2012). The indicators evaluated were derived from simulated catch or survey data, for example, for the body mass or current length of individual fish, their expected length at first maturation, or trophic level, which were aggregated according to a number of formulae proposed in the literature (see Houle et al, 2012 and references therein).…”

Stock–recruitment relations controlled by feeding interactions alone

“…Most aspects of the FCSRM have been described and motivated in great detail by previous authors (Andersen and Pedersen 2010;Hartvig et al 2011;Houle et al 2012). Here, the model structure is outlined just as much as required to interpret simulation results.…”

“…Food intake of individual fish is determined by a bell-shaped predator-prey size ratio (PPMR) window (here in a modified form following Houle et al (2012)), a trophic link strength θ ij , depending on the species identities of prey i and predator j, and a Type II functional response to prey availability. Assimilated food is first discounted by density-independent respiration, and the remainder is invested into growth, g j (m), and reproduction, g r,j (m), both of which depend on individual body mass m and species identity j.…”

“…The model we study is a variant of the Fish Community Size Resolved Model (FCSRM) (Hartvig et al 2011;Andersen and Pedersen 2010;Houle et al 2012), developed based on theory by . In this model, individual fish interact exclusively through predator-prey relationships.…”