The Exxon Valdez Oil Spill and the Collapse of the Prince William Sound Herring Stock

The Prince William Sound Pacific herring stock sustained an annual harvest averaging over 8,000 tons from 1974 to 1992.  In 1993, fishers were not able to find concentrations of herring despite a management forecast for a substantial herring biomass.  Subsequent research revealed that the herring population had collapsed.  A link to the 1989 Exxon Valdez Oil Spill was not made because of the four-year gap between the spill and the collapse.  Fisheries management data, especially age-structured-assessment (ASA) models, suggested a high adult biomass until 1993.  Consequently, a massive disease outbreak was suggested as the cause of the collapse despite a lack of disease monitoring prior to 1994.  This consensus was challenged by the authors in a 2003 paper based on historical measurements of the magnitude of male herring spawning.  Subsequent research, including hindcasts from new ASA models, show that at least 50% of the collapse occurred shortly after the oil spill and was likely a direct mortality on adult herring from contact with surface oil.  The results show that fishery-dependent methods have limited ability to detect acute mortalities in adult populations.  Detection and quantification of such impacts require precise direct measurements.