Effect of hypoxia on rockfish movements: implications for understanding the roles of temperature, toxins and site fidelity

We used a high-resolution acoustic telemetry array to study the effect of seasonal hypoxia (defined as dissolved oxygen concentration [DO] < 2 mg l(-1)) on the movements of quillback rockfish Sebastes maliger and copper rockfish S. caurinus at Cape Perpetua Reef, Oregon, USA. Over 18 weeks in summer 2010, a period with both normoxic and hypoxic conditions at the reef, both species showed high site fidelity. Home range was variable within species, was much larger than previously shown, and was influenced by foray and relocation behavior. Several quillback rockfish forayed well off of the reef into sand and gravel areas. Foray departure time was synchronous among individuals and related to time of day (sunset). Hypoxic conditions reduced home range for copper rockfish by 33%, but home range was variable for quillback rockfish, with no change in foray behavior. We propose that the origin, chemistry, and temperature of the hypoxic water mass and the species' innate behavioral tendencies must be considered, along with DO, in determining the effects of hypoxia on fish.