Feeding ecology and movement patterns of juvenile sablefish in coastal Southeast Alaska

Abstract

Sablefish, Anoplopoma fimbria, is a commercially valuable groundfish species undergoing population declines in the Gulf of Alaska and Bering Sea. This study assessed the role of juvenile sablefish as consumers in coastal Southeast Alaska (St. John Baptist Bay, Baranof Island, Alaska; SJBB) to better understand their use of habitat and food resources during their early life history. Specifically, the diet of juvenile sablefish was described for multiple seasons (summer and fall) and years (2012 and 2013) from analysis of stomach contents recovered using gastric lavage. Sablefish ate a wide variety of prey taxa, and the most important prey groups were Pacific herring, smelts, and scavenged salmon remains. Diet differed between seasons and years, and scavenging of salmon carcasses occurred during fall sampling periods, revealing the ability of sablefish to capitalize on pulsed, high energy prey. We further explored habitat use by juvenile sablefish within SJBB by analyzing their vertical movement patterns using acoustic telemetry data. Sablefish that were frequently detected remained predominately near the bottom, but all fish remaining in range of the acoustic receivers made short excursions into shallower water. Generalized linear mixed models were used to determine the relationship between excursion frequency and daylight and tidal cycles. The excursion frequency was highest during slack and flood stages and at dawn and may be linked to foraging. Together, these findings suggest that juvenile sablefish may maximize their growth by accessing high energy pelagic and benthic prey while remaining on the bottom for the majority of time, potentially decreasing risk of predation.