Catchability is crucial for the economic performance of fisheries and their
management. However, in many bio-economic simulation models it is assumed to
be either constant or it is largely ignored, despite the fact that it is
known to vary due to technical, environmental and behavioral factors. Such
variation can cause the relationship between effort and fishing mortality to
be nonlinear. This paper provides evidence for the possibility of nonlinear
optimizing behavior from the Dutch beam trawl fishery, provides a
methodology for estimating the curvature of the resulting relation, and a
simple way of implementing these processes within a bio-economic model.
Moreover, it shows the influence of a nonlinear relationship between effort
and fishing mortality in a model of effort management (EU long-term flatfish
management plan).