A model for evaluating fishing impacts on habitat and comparing fishing closure strategies

Abstract

In response to increasing concern with the effects of fishing on benthic habitat, I show a mathematical model using state transition equations to compute habitat reduction by unifying the processes of fishing impact and habitat recovery. The model assumes habitat is either in an unimpacted state or in an impacted state. The state transition equations describe that fishing decreases unimpacted habitat and the recovery process decreases impacted habitat. The equations are integrated under constant fishing effort for habitat trajectories over time, and the equilibrium habitat level is derived. A difference equation is also derived to model habitat trajectories under varying fishing effort. An exploration of the joint properties of the habitat reduction and catch equations provides guidance in choosing or designing habitat protection measures. Illustrations with the model demonstrate that when harvest levels are maintained, closing heavily fished areas rather than lightly fished areas can result in increased habitat reduction.