Size‐dependent, Spatial, and Temporal Variability of Juvenile Walleye Pollock (Theragra chalcogramma) Feeding at a Structural Front in the Southeast Bering Sea

Abstract

Abstract. The waters surrounding the Pribilof Islands are an important nursery ground for juvenile walleye pollock (Theragra chalcogramma), an important forage fish in the pelagic food web of the productive Bering Sea shelf region. The diet of juvenile pollock was studied in two consecutive years along a transect line crossing from a well‐mixed coastal domain, through a frontal region to stratified water farther offshore. Variability in stomach fullness was high and evidence for increased feeding intensity in the front was weak. Prey diversity and prey size generally increased with increasing fish size, shifting from predominantly small copepods to larger, more evasive prey items such as euphausiids, crab megalopae and fish. The diet of the fish reflected changes in the relative abundance of copepods and euphausiids in the prey fields between years. Juvenile pollock showed increased feeding rates at dusk, and stomach fullness as well as prey condition were generally lowest just before sunrise; however, the proportion of euphausiids increased in the diet of pollock caught at night, suggesting that some food was also ingested during darkness. Juvenile pollock and their euphausiid prey both vertically migrated above the thermocline at night, although each had a different daytime depth.

Factors affecting summer distributions of Bering Sea forage fish species: Assessing competing hypotheses

“…Age-0 pollock distributions have also been reported as being independent of feeding habitat quality as inferred from body condition and stomach fullness (Schabetsberger et al, 2003).…”

“…Studies have inferred, but not directly tested, that temperature (Miyake et al, 1996;Moss et al, 2009), proximity to fronts (Schabetsberger et al, 2003;Swartzman et al, 2005), the extent of the cold pool (Wyllie-Echeverria and Wooster, 1998), and zooplankton abundance (Swartzman et al, 2002) may influence forage fish species distributions. Other studies have statistically evaluated relationships using small numbers of explanatory indices, suggesting that SEBS forage fish species distributions are related to bottom depth Hollowed et al, 2012;Hurst et al, 2012), temperature Ciannelli and Bailey, 2005;Hollowed et al, 2012;Hurst et al, 2012), prey abundance and/or overlap with predators (Swartzman et al, 1999;Ciannelli et al, 2002;Winter and Swartzman, 2006;Winter et al, 2007), habitat energetics (Ciannelli, 2002), cohort size (Hurst et al, 2012), thermal regime (Ciannelli and Bailey, 2005;Hurst et al, 2012), and latitude (Hurst et al, 2012).…”

Nested scales of spatial heterogeneity in juvenile walleye pollock Theragra chalcogramma in the southeastern Bering Sea

“…At the largest scales, the distribution of young-of-the-year pollock is affected by the spawning patterns in adult fish (Bacheler et al 2012), as well as the survival and recruitment of the resulting offspring (Bailey et al 2005). At scales of kilometers, patchiness of youngof-the-year pollock is likely driven largely by advection, including re gional circulation and more localized ocean frontal patterns (Schabetsberger et al 2003) because of the limited swimming capacity (Ryer & Olla 1997) of these small fish. At smaller scales, juvenile pollock distributions are related to intrinsic factors like hunger and stress, physical factors including light and turbulence, and biotic factors including social interactions and prey (Bailey 1989.…”

Interannual changes in distribution of age-0 walleye pollock near the Pribilof Islands, Alaska, with reference to the prediction of pollock year-class strength

“…We utilized this database to investigate the potential of Pribilof age-0 pollock as an early predictor for year-class strength by analysing the acoustically derived biomass indices in the context of (i) the distribution of age-0 pollock in relation to the distribution of euphausiids, a major prey item Schabetsberger et al, 2000Schabetsberger et al, , 2003Ciannelli et al, 2004); (ii) the distribution of age-0 pollock in relation to the distribution of groundfish and seabird predators; and (iii) the distribution of age-0 pollock in relation to frontal regions and relative northesouth (latitudinal) distance from the Pribilof Islands. Interannual variations in these acoustic density and distribution relationships were then compared with the subsequent abundance of EBS pollock year classes at recruitment (age-3).…”