FISHING DISEASED ABALONE TO PROMOTE YIELD AND CONSERVATION

Disease is an important source of mortality in fished populations but options for disease intervention are rarely considered in fisheries management. Theoretical models suggest that fishing disease-impacted stocks is a cogent strategy to reduce parasite transmission but only when the level of exploitation required to reduce transmission is not so high as to overfish the stock. We applied this concept in a mathematical model of disease in a red abalone fishery so heavily impacted by an infectious disease (withering syndrome) that stock densities plummeted and the fishery was closed. We compared a strategy of parasite eradication through the targeted fishing (culling) of infected individuals with that of fishing that was non-selective with respect to disease.

Targeted fishing is possible because modern diagnostic tools make it possible to determine infection without compromising hosts, and the cost of diagnosis is minor relative to the value of the catch. We demonstrate that the level of non-selective fishing required to eradicate parasites altogether far exceeds thresholds for sustainability, but that targeting infected abalone allows the fishery to generate yield and reduce parasite prevalence while maintaining stock densities at or above the densities attainable if the population was closed to fishing. Disease control through harvest is possible even when uninfected abalone are included in the catch. In practice, directly targeting diseased hosts presents fishery managers with new challenges that can be met with adaptive approaches.