Integration of Disease Information into Population Assessments: The Case of VHS and Pacific Herring

Infectious diseases can have significant impacts on wild fish populations. However, disease information is rarely integrated into population assessment models or resource management plans.  An exception involves incorporation of disease metrics into an Age Structure Analysis (ASA) model for forecasting abundance of Pacific herring in Prince William Sound, AK.  Disease inputs for the ASA model include lesion scores for viral hemorrhagic septicemia (VHS) that are used to estimate the portion of annual mortality attributable to disease.  Unfortunately, extrapolation of these data into an annual mortality estimate is not supported by known VHS epizootiological principles. We offer an approach based on known host / pathogen relationships for forecasting disease potential in Pacific herring populations. Laboratory and field studies indicate that the key determinant for forecasting VHS epizootics involves understanding herd immunity within a population.  Here, we describe our ongoing efforts to develop laboratory tools capable of quantifying herd immunity and providing a measure of future potential for VHS epizootics in a population.  The implications of this information for fisheries management will be discussed.  We conclude that incorporation of meaningful disease information into population assessment models should be based on epidemiological principles specific to the particular host / pathogen system of interest.