Movement patterns of black rockfish (Sebastes melanops) in Oregon coastal waters

We studied the movement patterns of black rockfish (Sebastes melanops) in Oregon coastal waters to estimate home range over daily to annual time scales, determine if females relocate during the reproductive season, and evaluate the influence of environmental variation on movement. We moored 18 acoustic receivers in a 3 × 5 km array south of Newport, Oregon, at depths from 9 to 40 m. We then surgically implanted 42 black rockfish (34-48 cm total length [TL]) with coded, pressure transmitters having an approximate lifespan of 6 months. Fish were tagged in August (n = 6), September (n = 13), October (n = 7), and February (n = 8 depth and 8 non-depth). Fish were temporarily absent from the monitored area for short periods (usually 39 cm (likely mature) from the array were longer in duration than for mature males, especially during the reproductive season (November, January, and February), but both sexes had the longest absences during April through July. These data indicate that black rockfish in open coastal waters live in a very restricted area for long periods as adults, but may relocate periodically. A small home range could make them susceptible to local depletion from targeted fishing, but also make them good candidates for protection using marine reserves. 40 Parker et al.—Movement Patterns of Black Rockfish Introduction Understanding movement patterns and behavior is fundamental to understanding the ecology of a species. Defining an area of normal activity or home range and determining home range size stability is critical in developing strategies to manage local populations (Vincent and Sadovy 1998). In the nearshore environment along the northeast Pacific coast ( 7 m). In addition to logistical challenges, most rockfish suffer barotrauma when captured due to the expansion of gas in their physoclistic swim bladder (Parker et al. 2006). This trauma makes choosing an individual likely to survive capture more risky, makes surgical tagging more difficult, and requires additional studies to conclude that the barotrauma has no significant impact on subsequent movement behavior. Few acoustic telemetry studies of rockfish exist for these reasons. These telemetry studies have typically addressed only a few of these constraints, often by facing great logistical hurdles (Matthews 1990; Pearcy 1992; Starr et 41 Biology, Assessment, and Management of North Pacific Rockfishes al. 2000, 2002). Our study used receiver moorings specifically designed to withstand wave and current action for long periods, yet be periodically retrievable by boat. We also removed excess swim bladder gas at the surface and used surgical implantation of transmitters. Our objectives were to document annual, seasonal, and diel movement patterns of black rockfish, estimate home range size under different environmental conditions, and evaluate female movement during the reproductive season off the Oregon coast. Understanding black rockfish movement patterns with high resolution on both short and long time scales will provide fundamental information necessary to define local population characteristics, movement patterns and pathways, make habitat associations, and aid in the design of MPAs. Materials and methods Study area and acoustic array This study was conducted in the Pacific Ocean near Newport, Oregon, at depths of 9-40 m, within an area normally fished by the recreational groundfish fishery (Fig. 1). We monitored the study site using a rectangular array of 18 VR2 69-kHz omni-directional acoustic receivers (Vemco Ltd., Nova Scotia, Canada) designed to monitor for transmitters in a 1,500 hectare area. The receivers were individually anchored on single buoy lines according to manufacturer specifications, approximately 5 m off bottom. The receivers recorded tag code, receiver number, date, time, and depth of the transmitter (for depth transmitters) at a known location. Range testing showed a normal detection range of 350-500 m radius, and receivers were spaced 700 m apart to allow tags to be detected by more than one receiver. Some receivers were moved slightly to avoid shielding by observed bathymetric features. If during the study, a receiver was lost, it was replaced as soon as possible. We also moored a tag within the array for 27 days to provide an indication of horizontal positioning accuracy and precision. Tagging Fish were captured by barbless hook and line fishing throughout the study area using typical recreational fishing gear periodically from August 2004 through February 2005. We attempted to catch and tag fish throughout the monitored area to minimize transmission interference from multiple tags in the same area and to gather data on fish living at different depths. Coded acoustic V-13 HP transmitters (69 kHz, pressure sensitive [0-50 m] 155 dB output, 13 × 42 mm) were programmed to transmit at a random period of between 30-90 seconds, giving an expected battery life of 6 months (Vemco Ltd.). Black rockfish (34-48 cm TL) were vented to release excess pressure from the expanded swim bladder using an 18 gauge hypodermic needle. No anesthesia 42 Parker et al.—Movement Patterns of Black Rockfish

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