Seasonal changes in the diel vertical migration of walleye pollock (Theragra chalcogramma) in the northern Gulf of Alaska

Abstract

Walleye pollock (Theragra chalcogramma) perform diel vertical migration (DVM) as juveniles, but have an increasing tendency to be associated with the bottom with age. We studied the DVM of a local population of adult pollock in the northern Gulf of Alaska in August and November 2003. There was no relationship between the depth of pollock and the isolume (line of equal light intensity) necessary for visual foraging in August. Pollock passed through the thermocline at this time. In November there was a significant relationship between pollock biomass above/below the 200 m isobath and the isolume necessary for visual foraging. It is hypothesized that in August pollock ignore the isolume and thermocline, simply tracking the movements of their prey (euphausiids) to feed upon them near the surface at night. In November, relatively denser pollock shoals migrate up and down with the isolume necessary for visual foraging to feed on decapods.

Temporal and Ontogenetic Variability in Trophic Role of Four Groundfish Species—Walleye Pollock, Pacific Cod, Arrowtooth Flounder, and Pacific Halibut—around Kodiak Island in the Gulf of Alaska

“…Smaller walleye pollock and Pacific cod had higher TL values in winter relative to other seasons, but for larger fish seasonal differences were less apparent. The seasonal variations we observed in the trophic positions of walleye pollock and Pacific cod corresponded well with the few seasonal diet studies on gadids in the GOA (Albers and Anderson 1985;Adams et al 2007Adams et al , 2009). In the northern GOA, walleye pollock consumed primarily euphausiids in May and August 2003, while in November their diet shifted to one that was more dominated by decapods, mostly pandalid shrimp (Adams et al 2007(Adams et al , 2009).…”

“…The seasonal variations we observed in the trophic positions of walleye pollock and Pacific cod corresponded well with the few seasonal diet studies on gadids in the GOA (Albers and Anderson 1985;Adams et al 2007Adams et al , 2009). In the northern GOA, walleye pollock consumed primarily euphausiids in May and August 2003, while in November their diet shifted to one that was more dominated by decapods, mostly pandalid shrimp (Adams et al 2007(Adams et al , 2009). In addition, a period of fasting can also result in inflated δ 15 N signatures (Hobson et al 1993), and particularly for smaller size-classes of walleye pollock and Pacific cod, fasting is likely to occur in winter (Heintz and Vollenweider 2010).…”

Seasonal changes in depth distribution of salmon sharks (Lamna ditropis) in Alaskan waters: implications for foraging ecology

“…Although the diet of salmon sharks in coastal Alaska outside of the period of the summer salmon runs has not been described, there are a variety of organisms known to be consumed by salmon sharks that also exhibit DVM, including Pacific herring (Hay and McCarter 1997;Mackinson 1999), capelin (Mallotus villosus) (Mowbray 2002;Wilson et al 2003), pollock (Brodeur and Wilson 1996a;Adams et al 2007;Adams et al 2009), salmon (Walker et al 2007), and squid (Teuthoidea) (Roper and Young 1975;Watanabe et al 2006). Salmon exhibit DVM; however, the extent of their vertical movements is much more limited and primarily restricted to the upper 20-40 m (Walker et al 2006), suggesting that this behavior is not primarily related to salmon.…”

“…Pollock are known to vertically migrate from deeper diurnal depths to shallow nocturnal depths to forage (Brodeur and Wilson 1996a;Wilson et al 2003;Adams et al 2009). In the GOA, juvenile pollock rise in the water column at night to form diffuse layers concentrated at shallow depths (10-40 m) to forage (Brodeur and Wilson 1996a;Adams et al 2007) and descend to deeper depths (around 90-150 m) in the daytime where they form tight ball-like aggregations (Brodeur and Wilson 1996a;Wilson et al 2003), likely as an antipredation tactic (Brodeur and Wilson 1996b).…”

Seasonally Dynamic Diel Vertical Migrations of Mysis diluviana, Coregonine Fishes, and Siscowet Lake Trout in the Pelagia of Western Lake Superior

“…For example, M. diluviana migrate less extensively in spring than in other seasons and are found throughout the water column at night, probably because of isothermal conditions in the Great Lakes during that time period (Gal et al 2004;Boscarino et al 2009). For some fish species, such as juvenile kokanee Oncorhynchus nerka and walleye pollock Theragra chalcogramma, DVM patterns are influenced by seasonal changes in water temperature, light, and prey-predator densities and distributions (Hardiman et al 2004;Adams et al 2009). However, for the vendace Coregonus albula and Fontane cisco Coregonus fontanae, the DVM patterns do not change significantly by season (Mehner et al 2007).…”