Mitigating Impacts of Natural Hazards on Fishery Ecosystems

<em>Abstract</em>.—The impacts of hypoxia on fishes have been studied in shallow estuaries of the eastern coast of the United States and in Europe, but only recently has hypoxia received attention on the West Coast of North America. Hypoxia has had a dramatic impact on fish populations in southern Hood Canal, Washington, a long, narrow fjord characterized by weak flushing. We have used visual surveys while on scuba to track the abundance and depth distribution of rockfishes, lingcod <em>Ophiodon elongatus</em>, and other marine fishes at the Sund Rock Conservation Area in southern Hood Canal since 2001. By correlating ambient oxygen concentrations with fish abundance and by relating fish kills to oxygen concentrations, we are developing a model for predicting when fish will avoid or be killed by low oxygen events. Copper rockfish <em>Sebastes caurinus </em>avoid oxygen concentrations below 2 mg/L but can tolerate concentrations to 1 mg/L. Other marine fish species show similar responses, but smaller fish and species appear to be affected more than larger ones. Fish kill events are not consistent between years, affecting rockfish in one instance and lingcod in another. Differences in behavior and lethality during hypoxic conditions may relate to the magnitude and duration of exposure, temperature, past experience, and physiology. Recent and past fish kill events have resulted in long-term impacts reducing populations of rockfish and lingcod at Sund Rocks by one-third. Based on our results, continued efforts to minimize other population stressors are warranted.