Effects of Marine Reserves on Behaviorally Mediated Changes in Spawning Success of California Sheephead

In the first year of this project, researchers assessed the effects of the Catalina Island marine reserve on fish density, biomass, size structure, sex ratios and habitat preferences. For the period 2011–12, they plan to document territorial, courtship and spawning behaviors to test whether the reserve is restoring normal social behavior and enhancing reproductive output. Within the reserve, the hypotheses to be tested are: (1) males will spend more time courting females; (2) the rate of spawning success will be greater; and (3) territory sizes will be different. The Sea Grant trainee on the project is leading manipulated predation experiments inside and outside the marine reserve to document sheephead prey preferences and predation rates on sea urchins as a function of sheephead size. Preliminary findings suggest that sheephead do not begin consuming urchins until the fish are at least 30-centimeters long, the minimum size limit for the sheephead fishery. Diver surveys also show that urchin predation rates are higher in protected areas. Findings suggest sheephead may not be able to control herbivory by urchins at heavily fished sites and that marine reserves could preserve sheephead’s historical role as an urchin predator. Findings were shared with managers and the scientific community at a Sea Grant-sponsored sheephead workshop held at UC Santa Barbara in April 2011.