Can an abalone in the bag save two in the bush? Impacts of fishing on the transmission of withering syndrome

Background/Question/Methods

An explicit consideration of pathogens into fisheries management can profoundly shift reference points and criteria for sustainability. By driving host populations below thresholds for transmission, fishing supports a number of desirable outcomes, including the extirpation, or fishing out, of pathogens. Southern California abalone fisheries closed in 1996 due to a combination of heavy exploitation and withering syndrome, a fatal infectious disease caused by a Rickettsiales-like pathogen (WS-RLP). Although this disease remains enzootic in southern California, red abalone (Haliotis rufescens) populations have shown widespread signs of recovery, particularly at San Miguel Island, and the re-opening of a small-scale, limited access fishery is currently proposed for this region. I constructed an age-structured epidemiological model, parameterized by fisheries-independent demographic and epidemiological data, to test and predict how harvest could both provide fishery benefits and enhance the recovery of red abalone at San Miguel Island.

Results/Conclusions

I show that a limited effort fishery can enhance the recovery of red abalone, however only when the minimum size limit (MSL) is maintained below the MSL prior to the closure of the fishery. Fishing fails to fish out WS-RLP at high MSL, and results in overexploitation at low MSL. Both effort and MSL must therefore be strictly maintained to maximize the persistence of red abalone, and the red abalone fishery, at San Miguel Island. These results will have widespread implications for epidemiological theory and the management of fisheries in the face of enzootic disease.