Patterns in vertical movements of black rockfish Sebastes melanops

Abstract

Black rockfish Sebastes melanops are generally associated with benthic structure, but are also described as semi-pelagic and are frequently found near the surface. We described patterns associated with the vertical movements of 33 black rockfish using acoustic telemetry in the nearshore waters of the Northeast Pacific Ocean off Newport, Oregon (9 to 45 m depth). The fish were moni-tored by an array of 18 moored receivers for a 12 mo period. Black rockfish showed larger, more frequent, and more temporally structured vertical movements throughout the study period than are typically assumed for rockfishes, which may make hydroacoustic surveys difficult to design. Diel vertical movements occurred sporadically, with individuals sometimes being shallower either during day or at night, and the pattern was often maintained for more than a week. Periods of large vertical movements (multiple excursions >5 m not in synch with diel phase) were most common during the months of October and May. The diel behavior of being shallower at night was most common during spring months and showed a slow decline in prevalence throughout the summer months. The reverse pattern (shallower depths during daylight hours) was less common overall, but most prevalent in autumn. These data show that black rockfish make extensive vertical movements, often tightly in phase with sunrise or sunset, and that several behaviors, such as diel vertical migration, may be more prevalent at certain times of the year. © Inter-Research 2008.