| Despite the importance of pathogens in natural populations, little attention has been given to host-pathogen dynamics in fisheries management. Here, I developed a fishery research program and designed a series of experiments and management models to evaluate the consequences of incorporating an explicit consideration of pathogens in the management of southern California abalone fisheries.;A controlled, laboratory experiment was conducted testing the influence of environmental variables on key processes of withering syndrome (WS), a fatal disease of California abalones. Daily temperature variability associated with the intertidal environment increased the susceptibility of black abalone to infection, but disease expression occurred only at warm water temperatures and was independent of temperature variability. This result implies that high thermal variation of the marine intertidal zone allows WS to readily infect intertidal black abalone, but infected individuals remain asymptomatic until water temperatures periodically exceed thresholds modulating WS. Intertidal black abalone, but not other abalone species, went extinct locally throughout much of southern California following the emergence of WS, and results suggest that mass mortalities occur before pathogen transmission is limited by density-dependent factors.;I analyzed a 30-year data set of abalone abundance at 33 sites in Channel Islands National Park to investigate whether the presence of multiple hosts of WS contributed to the decline of red abalone. The presence of multiple hosts was associated with red abalone declines at the Channel Islands and population declines were pronounced with increasing water temperature. I developed a deterministic, density-dependent host-pathogen model, parameterized by field surveys and laboratory investigations of red abalone life history, to address how the addition of a tolerant host modifies the impact of WS on red abalone. A reservoir host increases the severity of disease-induced population declines, and allows pathogens to overcome density thresholds for transmission, driving focal hosts to near extinction. In the case of red abalone, this will occur when water temperatures are warm and the rate of mortality from WS is high.;A management strategy considering host-pathogen dynamics was developed for the California abalone fishery. I show that maximum sustainable yield is attained at a higher fishing effort and lower minimum size limit when disease processes are considered explicitly, and ignoring disease will underestimate potential yield available to the fishery. Including marine reserves as tool for managing diseased populations for harvest had mixed effects. Reserves protected against fishery collapse but increased host population densities within reserves maintained parasite transmission within the fished stock. I concluded by considering the special case where fisheries have prior knowledge of infection status allowing infected hosts to be targeted directly or culled. I found that supplementing harvest by targeting infected hosts directly can increase fishery yield and reduce parasite transmission, even when marine reserves are present. The results highlight how harvest strategies can be modified to consider disease processes explicitly and underscore the value of understanding the indirect consequences of fishing in the integrated management of marine resources. |
