Hypoxia has been identified as a major threat to marine ecosystem health in the world’s coastal waters including Puget Sound. This study is evaluating the potential effects of hypoxia on fish and zooplankton distributions in Hood Canal, WA, using multifrequency acoustics and net sampling. Field surveys were conducted monthly from June to October in 2012 and 2013 to characterize pre-, during, and post-hypoxia nekton distributions at four sites along the Canal. Using the repeated samplings and high-resolution survey data, we are examining how seasonal and inter-annual difference in the timing and intensity of hypoxia affects distributions of predators (primarily Pacific herring and Pacific hake) and prey (primarily copepods and euphausiids). Depth of the zooplankton backscatter layer changed seasonally with hypoxia intensity. Toward late-summer, the daytime zooplankton layer was closer to the surface, increasing the vertical separation between zooplankton and fish. In spite of low oxygen levels in late-summer, fish remained in low-oxygen regions of Hood Canal. This suggests a decrease in energy flow toward higher trophic level during hypoxia
