Ecology of Diseases in Pacific Herring

We provide several lines of evidence from field surveillances and controlled empirical studies indicating that population declines and demographic shifts in Pacific herring are associated with mortality from endemic diseases including viral hemorrhagic septicemia (VHS), viral erythrocytic necrosis (VEN), and ichthyophoniasis (Ichthyophonus disease).  For example the Pacific herring population in Prince William Sound, AK declined from 120,000 to 30,000 mt in 1993, and disease mortality represents a leading hypothesis accounting for the proximate cause of the population decline and failure of the population to recover in subsequent years.  Additionally, lines of evidence implicate diseases as primary drivers of failed recruitment of year classes into adult herring spawning populations throughout the NE Pacific, thereby resulting in concerning demographic shifts in age structures.  The advancement of new capabilities to study theses disease processes under controlled conditions is providing new insights into predisposing disease factors, including host and environmental conditions, which preface disease-related mortalities and population impacts.  Empirical relationships between some of these factors (i.e. temperature, herd immunity, and host behavioral patterns) will be discussed in the context of developing surveillance tools that are capable of forecasting and mitigating future disease impacts.