Horizontal and vertical distribution of juvenile pollock (Theragra chalcogramma) in the southeastern Bering Sea Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vh53wz509

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  • Juvenile walleye pollock (Theragra chalcogramma) are one of the primary prey items for bird and mammal predators in the Bering Sea and support a large commercial fishery. An understanding of the environmental factors that determine the horizontal and vertical distribution of juvenile pollock is needed to estimate the effects that environmental variation may have on pollock and their predators. During the summers of 2008 and 2009, surveys were conducted in three topographic zones (Middle Shelf, Outer Shelf, and Slope) near the Pribilof Islands in the southeastern Bering Sea. Environmental data collected for each transect included temperature, salinity, depth, dissolved oxygen, and chlorophyll a fluorescence. Additionally, each transect consisted of 10 km of multi-frequency acoustic sampling, a vertically integrated zooplankton net tow, and a targeted oblique fish tow. In 2008, juvenile pollock were found primarily in the Middle Shelf zone and were dominated by small young of the year individuals. In 2009, juvenile pollock were significantly less abundant, young of the year were larger, and vertical distributions were much deeper. In both years, juvenile pollock horizontal distribution was highly variable and not well explained by the physical environment. Temperature structure (thermocline depth, mean temperature at pollock depth, and mean temperature above the thermocline) explained 70% of the variability in the vertical distribution of age-0 pollock which also varied with time of day and topographic zone. These differences in horizontal and vertical distribution are likely to affect the use of habitat by predators and may have implications for future sampling.
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