Patterns and environmental drivers of juvenile sablefish movement in Southeast Alaska

Abstract

Sablefish Anoplopoma fimbria are a long-lived, deep-dwelling groundfish that inhabit the North Pacific Ocean, ranging from northern Mexico to the Gulf of Alaska to Japan, supporting one of Alaska's most valuable commercial fisheries. After decades of heavy fishing, declines in the Sablefish population led to significant fishing restrictions but few strong year classes developed in recent years. Most Sablefish research has focused on the larval, near-surface juvenile, or adult life history stages, but few studies have examined post-settlement juvenile Sablefish in nearshore areas. This study used acoustic telemetry to understand the presence and movement of juvenile Sablefish in a nursery area in Southeast Alaska. Throughout the summer and fall of 2015 and 2016, 40 juvenile Sablefish implanted with acoustic transmitters were monitored using an array of eight fixed receivers in St. John Baptist Bay, Baranof Island, Alaska. We quantified the movement patterns of 28 juvenile Sablefish using displacement from the head of the bay, daily distance traveled, daily duration within the bay, unique movement types among individuals, and movement in relation to environmental variables. From these analyses, we show that juvenile Sablefish exhibit fidelity to the middle-head region of the bay, display relatively high rates of daily movement and residence, demonstrate three distinct movement patterns, and are influenced by environmental variables like water temperature, diel state, moon phase, and day of year. Our results show that juvenile Sablefish exhibit seasonality in movements as they progressively emigrate from the bay throughout the summer and fall. Certain factors were found to increase the likelihood of movement for juvenile Sablefish, perhaps allowing them to remain in suitable environmental conditions. This study fills a gap in our knowledge of Sablefish early life history and reinforces the importance of nursery areas like St. John Baptist Bay for juvenile Sablefish prior to recruitment into commercial fisheries.