Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8435
Title: Vertical distribution of age 0 Walleye Pollock during late-summer: environment or ontogeny?
Author: Sandra L. Parker-Stetter, John K. Horne, Samuel Urmy, R. Heintz, Lisa B. Eisner, Edward V. Farley
Publication Year: 2015
Journal: Marine and Coastal Fisheries
Keywords: Bering Sea,Walleye pollock,environment,ontogenetic shifts,acoustics

Variability in the late-summer vertical distribution of age 0 Walleye Pollock (Gadus chalcogrammus) in the southeastern Bering Sea has been attributed to a range of physical and biological factors.  Using acoustic data (38, 120 kHz) collected during the 2010 Bering Aleutian Salmon International Survey (BASIS) and a dedicated high-resolution survey (HR), we evaluated whether late-summer distributions could be explained by water column properties (environment) or if sampling was likely occurring during the age 0 Walleye Pollock ontogenetic shift from the near-surface to demersal habitats (ontogeny). Environment: neither water column attributes (temperature, relative temperature, salinity, dissolved oxygen, density gradient) nor zooplankton prey (zooplankton acoustic density) strongly predicted acoustic estimates of age 0 Walleye Pollock vertical presence (R2 ≤ 0.27) or density (R2 ≤ 0.23).  Ontogeny: at 6 of 10 paired BASIS-HR1 stations, age 0 Walleye Pollock shifted deeper in the water column between sampling periods separated by 8-34 days (p < 0.05).  Neither age 0 Walleye Pollock fork length (p > 0.05 in 2 of 4 station pairs) nor energy density (p > 0.05 in 3 station pairs) was consistently different between fish caught near-surface and midwater.  Our data suggest that the observation of both near-surface and midwater age 0 Walleye Pollock in late-summer is likely due to ontogenetic habitat shift, but that the causative factor was not clear given limited sample sizes and explanatory variables.  Timing of the ontogenetic shift, which appeared to have begun prior to 18 August 2010, can ultimately affect survey strategies and provide additional insight into factors affecting overwinter survival.


Characterization of vertical distribution of age-0 Walleye Pollock, using acoustic and trawl data, and evaluation of whether observed spatial and temporal differences are likely due to environment or ontogeny.

Theme: Ecosystem approach to improve management of marine resources
Foci: Characterize ecological interactions (e.g. predation, competition, parasitism, disease, etc.) within and among species.
Official Citation:

Parker-Stetter, S., J. Horne, S. Urmy, R. Heintz, L. Eisner and E. Farley. Vertical distribution of age-0 pollock during late-summer: environment or ontogeny? Marine and Coastal Fisheries.