Diel vertical migration of sablefish (Anoplopoma fimbria)

Abstract

AbstractTo investigate their diel vertical migration (DVM), 599 sablefish (Anoplopoma fimbria) were implanted with electronic archival tags in the Gulf of Alaska, Aleutian Islands, and the eastern Bering Sea. Of these tags, 98 were recovered with usable depth data (7,852,773 recordings representing 81,233 days) that we used to identify DVM and to classify DVM into one of two types: normal DVM (rise from the bottom during nighttime) and reverse DVM (rise from the bottom during daytime). The results of our study highlight three important attributes of DVM for sablefish. First, all tagged sablefish carried out DVM, although the occurrence was intermittent (26% of the days with usable data) and most commonly for short durations (10 days or less). Second, bottom depth for normal DVM was about 78 m shallower than for reverse DVM. Third, normal DVM occurred most often in fall and least often in spring, whereas this high/low pattern was shifted about 3 months later for reverse DVM; reverse DVM occurred most often in winter and least often in summer. Normal DVM likely occurred to increase foraging opportunity (e.g., nightly shift to match depth of prey). Reverse DVM more commonly occurred during winter and may represent an increase in foraging by sablefish during the daytime to compensate for decreased pelagic resources. The default foraging strategy for sablefish may be benthic because of the uncertainty of vertically migrating to a location where the occurrence of prey is not guaranteed; sablefish may invoke DVM when the non‐DVM foraging benefit is reduced.