The Pacific herring population of Prince William Sound has not recovered from severe population decline in 1993. Viral hemorrhagic septicemia (VHS) virus and the fungus Ichthyophonus hoferi were identified as the two main diseases during a multi-year research project that closed out in FY 98 (Project /162). Prevalence of Ichthyophonus decreased after 1995, but an unexpected increase in the prevalence of VHS virus in 1997 might delay recovery.
This project covers: (1) survival of viral hemorrhagic septicemia (VHS) virus in sea water, (2) the natural history of VHS in wild herring, (3) serologic conversion and immunity in wild herring following an epizootic of VHS, and (4) age-related immunity demonstrated in laboratory-reared herring. Additional publications on the effect of net pens on VHS transmission and the presence of VHS-RNA in wild herring tissues as demonstrated by PCR (polymerase chain reaction) are also anticipated by this study.
Field and controlled laboratory studies will focus on viral hemorrhagic septicemia virus (VHS) and Ichthyophonus hoferi, a pathogenic fungus, to determine their role in the disease(s) and mortality observed in Prince William Sound herring since 1993.
The oil spill coincided with the spring migration of Pacific herring to spawning grounds in Prince William Sound. Studies of oil spill injuries to herring documented damage from oil exposure in adult herring, reduced hatching success of embryos, and elevated levels of physical and genetic abnormalities in newly hatched larvae. The Prince William Sound herring spawning population has drastically declined since 1993, and pathology studies have implicated viral hemorrhagic septicemia (VHS) and ichthyophonus as potential sources of mortality as well as indicators of stress.
This project will publish and present manuscripts of the results of the project done by Gary Marty, titled: "Investigations of Disease Factors Affecting Declines of Pacific Herring Populations in PWS", as they relate to effects of environmental contamination and disease on herring fitness. The effects of viral hemorrhagic septicemia (VHS) virus, Ichthyophonus hoferi, and hydrocarbon exposure were examined to determine their role in population declines experienced by Pacific herring populations in Prince William Sound in 1993 and 1994.
Field and laboratory studies will focus on Viral Hemorrhagic Septicemia (VHS) and Ichthyophonus hoferi, a pathogenic fungus, to determine their role in the disease and mortality observed in PWS herring since 1993. Herring in PWS will be monitored three times per year for signs of disease and immune status. Specific pathogen-free herring will be used to determine the degree of mortality, blood chemical changes and pathogenicity produced by these organisms alone and in combination with exposure to stressors such as petroleum hydrocarbons, temperature and crowding.
Viral hemorrhagic septicemia (VHS) and the associated virus (VHSV) were identified in newly metamorphosed Pacific herring Clupea pallasi and Pacific sand lances Ammodytes hexapterus captured from Puget Sound, Washington, between 1995 and 1998. During that 4-year period, virus was detected in less than 1% of free-ranging, age- Pacific herring; however, when groups of these fish were confined in the laboratory, they experienced severe mortality, occasionally exceeding 5 %, with the prevalence of VHSV reaching 1 % by 14 days postcapture.