Effect of viral hemorrhagic septicemia virus on Pacific herring in Prince William Sound, Alaska, from 1989 to 2005

Abstract

We critically review the role of viral hemorrhagic septicemia virus (VHSV) in the 1992-1993 collapse of the Prince William Sound (PWS) herring fishery. VHSV was detected in samples of moribund Pacific herring from PWS in spring 1993 when about 63% of the expected fish failed to appear. A low prevalence and severity of VHSV were observed in adult pre-spawning PWS herring in most of the years from 1994 to 2002. The North American strain of VHSV became established about 500 yr ago in many northeast Pacific marine fish species, including herring. In Alaska, the typical annual prevalence of VHSV in pre-spawning herring ranges from 0 to 17%. New threshold analysis of a 9 yr study indicates that only about half of the virus-infected adult fish in PWS were clinically affected; ulcers formerly attributed to VHS have been overestimated by a factor of about 3. We conclude that VHSV was not a primary causative factor in the PWS herring population collapse or in its failure to recover. Because older age classes of herring were not disproportionately missing in 1993, the protozoan Ichthyophonus hoferi was also not a likely cause of losses. The 'Exxon Valdez' oil spill occurred in PWS, Alaska, U.S.A., in 1989. Evidence for interaction of oil and VHSV expression is also evaluated. A study exposing herring to varying concentrations of weathered crude oil showed increasing prevalences of VHSV correlated with oil concentration; however, repeated experiments with juvenile and adult fish failed to corroborate these results or link oil to VHSV infection in herring.