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

Abstract

The 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 *Corresponding author: rhea.ehresmann@alaska.gov Received February 12, 2018; accepted June 27, 2018 This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Estuarine and coastal ecosystems have long been recognized as nursery grounds for crustaceans and fishes (Herke 1971;Weinstein 1979;Boesch and Turner 1984;Beck et al. 2001). Nursery habitats support ecological processes that contribute to recruitment success by improving growth and survival of juveniles, such as providing refuge habitat from predators, food resources, and favorable environmental conditions at a range of spatial and temporal scales (Heck et al. 2003;Nagelkerken et al. 2015;Sheaves et al. 2015). Assessing how juvenile fish use nursery areas may contribute to an understanding of the connection between postsettlement habitat and the population's vital rates (e.g., survival, recruitment, and emigration; Rutecki and Varosi 1997a;Hanselman et al. 2015; Pirtle et al., in press). One way to assess how juvenile fish use nursery ar...

A role for lakes in revealing the nature of animal movement using high dimensional telemetry systems

“…Telemetry combined with environmental monitoring can provide detailed information on habitat preferences of different fish species, especially on critical habitats such as spawning, feeding, and nursery grounds, which tend to be species-specific and temporally dynamic (e.g. [26,81,105]). Such data allows the development of detailed maps of critical habitats for multiple species through time in a given lake [275], generating tools to improve the environmental management, such as the selection of areas within lakes that have specific characteristics that favor only target species, while inhibiting the proliferation of invasive species [184,247].…”