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NOAA Technical Memorandum NMFS-AFSC-194

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Results of the echo integration-trawl survey of walleye pollock (Theragra chalcogramma) on the U.S. and Russian Bering Sea shelf in June and July 2008


Eastern Bering Sea shelf walleye pollock (Theragra chalcogramma) abundance and distribution in midwater were assessed between 2 June and 31 July 2008 using echo integration-trawl techniques aboard the NOAA ship Oscar Dyson. The survey also assessed walleye pollock in the Cape Navarin area of Russia.  Results showed that ocean conditions were cold in 2008, as in 2006 and 2007, compared to the previous 5 years.  Fewer pollock were observed east of 170°W than in 2007 and a larger percentage of those observed were inside the Steller sea lion Conservation Area (SCA).  The majority of the pollock biomass in the U.S. Exclusive Economic Zone (EEZ) was located to the west and southwest of St. Matthew Island between the 100 m and 200 m isobaths. Estimated pollock abundance in midwater (between 16 m from the surface and 3 m off bottom) in the U.S. EEZ portion of the Bering Sea shelf was 4.70 billion fish weighing 0.997 million metric tons (t); in the Russian EEZ, there were 58.6 million fish weighing 0.03 million t (3% of the total midwater biomass). East of 170°W (11% of total biomass) the predominant length mode was 55 cm inside the SCA and 51 cm outside the SCA. In the U.S. west of 170°W (86% of total biomass) modal lengths were 23, 32 and 47 cm.  In Russia, modal lengths were similar to those in the U.S. west of 170°W with proportionally more adults and fewer juveniles. Age results indicated that inside the U.S. EEZ, age-2 and -3 fish were dominant numerically (62% and 22%, respectively) and together represented 46% of the total biomass. Walleye pollock ages 4+ totaled 16% of the population numerically and made up 53% of the total biomass.  Age-1 pollock accounted for only 1% of the total estimated numbers and less than 0.1% of the biomass.  Analyses of walleye pollock vertical distribution indicated that 93% of adult biomass was within 40 m of the seafloor.  Juveniles were found both near the seafloor and higher in the water column;
21% of juvenile biomass was within 60 m of the surface.

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