Comparison of Harvest Control Policies for Rebuilding Overfished Populations within a Fixed Rebuilding Time Frame

Abstract

U.S. law requires that overfished fish populations be rebuilt within 10 years when biologically possible, and otherwise within the time it would take to rebuild in the absence of fishing plus one mean generation time (MGT). Most overfished populations can recover in less than 10 years; the exceptions are populations with very low productivity and some that are severely depleted. A range of harvest control policies, including constant fishing mortalities and variable harvest rate control rules, were compared in terms of their ability to rebuild overfished populations of five species within the required times. The North Atlantic swordfish Xiphias gladius and Gulf of Mexico red snapper Lutjanus campechanus populations were able to rebuild in 10 years, but the white marlin Tetrapturus albidus, sandbar shark Carcharhinus plumbeus, and darkblotched rockfish Sebastes crameri populations were not. The harvest policy that resulted in populations being rebuilt most rapidly was either a control rule that reduced fishing mortality with decreasing biomass or a constant harvest rate designed to meet the current rebuilding time requirement. The control rules we analyzed restricted catches at the beginning of the rebuilding period but allowed catches to increase rapidly as the population was rebuilt. Thus, there was a trade-off between relatively high catches early in the rebuilding period and high catches later in the rebuilding period when the population had been rebuilt and could sustain high catches. Whether the population was rebuilt more rapidly under a fixed rebuilding-time requirement or a control rule depended on the productivity of the population.