Movement Patterns of Juvenile Sablefish within a Nursery Area in Southeast Alaska

Abstract

AbstractThe Sablefish Anoplopoma fimbria is a commercially important species that inhabits waters of the Pacific Ocean from Baja California, Mexico, to the Bering Sea, Alaska. Most studies have focused on the larval, neustonic (near‐surface) juvenile, or adult stage of the Sablefish life cycle, while much less is known about the postsettlement juvenile stage (ages 0–2) in nearshore nursery areas, even though survival of postsettlement juveniles is thought to be important for determining year‐class strength. We used acoustic telemetry to monitor movement of postsettlement juvenile Sablefish in a nursery area in Alaska to better describe their period of nearshore residency. Forty juvenile Sablefish received surgically implanted acoustic transmitters and were monitored using eight fixed receivers throughout the summer and fall of 2015 and 2016 in a small bay (St. John Baptist Bay) in Southeast Alaska. We quantified movement patterns in terms of displacement from the head of the bay, distance traveled, and duration of time spent within the bay for 28 individuals. Sablefish showed fidelity to the bay during the summer, with relatively high rates of movement within the bay. Juvenile Sablefish traveled 9.4 km/d and spent 20.2 h/d within the bay on average in 2015 and traveled 13.0 km/d and spent 17.9 h/d within the bay on average in 2016. Tagged Sablefish showed the greatest affinity for a region near the head of the bay, perhaps indicating an area of preferred habitat, prey resources, or environmental conditions. In addition, we assessed variation in horizontal movements among individuals and identified three distinct movement types. This study fills a gap in knowledge of Sablefish early life history by characterizing movement during nearshore residency before out‐migration into deeper waters. Our results reinforce the importance of nearshore habitats like St. John Baptist Bay for juvenile Sablefish prior to recruitment into fisheries.