Movements of small adult black rockfish: implications for the design of MPAs

Off the coast of central California, USA, small black rockfish Sebastes melanops (individuals below the length at 50% maturity) comprise a large percentage of the catch in recreational fisheries, yet little is known about the movements of these small fish. To better understand their movements, we implanted acoustic transmitters into 23 black rockfish (29 to 41 cm total length) in Carmel Bay, California, USA. Tagged fish were monitored over a 16 mo period between August 2006 and January 2008. Their vertical movements were correlated with environmental variables such as atmospheric pressure, wind speed, upwelling, and wave height. From October to May, black rockfish moved to deeper waters offshore during the day and returned at night. In the summer, diurnal movements of black rockfish decreased in frequency, perhaps due to locally abundant food resources associated with seasonal upwelling. About two-thirds of the tagged black rockfish (14 fish) displayed a high degree of residency to the study area (>11 mo). The remaining third (9 fish) left the study area within 6 mo of release; signals from 4 of these fish were later detected on other acoustic receiver arrays >50 km north of Carmel Bay. Storms may have caused those fish to move northward in winter. When in residence, the mean home range of tagged fish was 0.25 km². Our results indicate that a better understanding of the variability of fish movements among age classes is necessary to design marine protected areas (MPAs) that are intended to protect all life stages of a species.