The dynamics of exploited marine fish populations and Humpty Dumpty: similarities and differences

Abstract

Marine fish populations of the global oceans and particularly large‐bodied, continental shelf‐dwelling groundfish species of the North Atlantic, such as cod (Gadus morhua), have been strongly perturbed by over‐fishing, frequently beyond levels that may have altered their capacity to recover. Age and size structure, spatial structure, reproductive potential, and other traits that convey fitness advantages are commonly lost when prolonged and excessive fishing pressure is exerted. Fisheries management protocols implemented to recover collapsed populations have been numerous and varied with all attempting to reduce or eliminate fishing pressure. Such measures, employed singly or in multiple combinations, typically involve quota reductions or fishing moratoria, area closures and other technical measures, as well as enhanced enforcement of fishing practices. A striking geographic pattern exists in the efficacy of such measures to regain lost population attributes and hence recovery. Some regional populations have recovered while others, despite management interventions lasting decades, notably, but not exclusively, those aimed at cod populations of the Northwest Atlantic, have yet to fully recover, an endpoint analogous to the conclusion of the famous nursery rhyme of Humpty Dumpty. Here we examine the dynamics of multiple collapsed populations exhibiting varying responses to recovery initiatives from the perspective of the Humpty Dumpty metaphor.