Marine diseases are being detected with increasing frequency and can cause significant ecological, economic or social impacts. Outbreaks that cause such impacts can be considered 'emergencies' and should be managed. Effective disease management requires surveillance of at-risk populations, forecasting future disease events and mitigating disease and downstream impacts,, However, knowledge gaps frequently hinder these management steps. Common knowledge gaps include: identification of etiological agent(s) of disease, quantification of environmental facilitators of disease, knowledge of population structure and migratory pathways of host populations and quantification of transmission pathways.
Epizootic shell disease in American lobster (Homarus americanus) is one of many examples in which management decisions are necessary before key knowledge gaps can be filled. First detected in 1997, this disease is characterized by polymicrobial infection or dysbiosis of the chitin exoskeleton and is contributing to the collapse of the Southern New England (SNE) fishery. Lobsters are one of the most lucrative fisheries in North America the SNE collapse has raised concerns that ESD will outbreak in the Gulf of Maine and Georges Banks stocks. This is an on-going marine disease emergency requiring both mitigation of current impacts and forecasting to predict future outbreaks. We used demographic analyses of a 30-year mark recapture dataset to estimate the impact of SNE on lobster populations and identify life stages most impacted by disease. In order to forecast disease risk, we determined sea bottom temperatures associated with disease prevalence greater than 5% in SNE. We then used the newest generation of IPCC climate models, forced with several emissions scenarios, to create long-tem projections of ESD risk under climate change.
Results/Conclusions
Disease impacts were severe within the SNE lobster population; relative survival of visually diseased lobsters was 56% that of lobsters without disease signs and 32.5% lower for diseased ovigerous females. The higher mortality rate of ovigerous females leads to a 43% decrease in the pre-harvest reproduction potential. Further research can determine the impact of reducing fishing on ovigerous females, but our results suggest that this may be limiting population growth. Sea bottom temperatures greater than 12 °C were associated with high disease prevalence in SNE. Climate model projections suggest that temperatures will meet and exceed 12 °C in most of the Gulf of Maine fishery and in southern Nova Scotia within the next 20 years. The climate model projections will be refined as more disease data becomes available and as other risk factors are identified.