Book Description

Eastern Bering Sea shelf walleye pollock (Theragra chalcogramma) abundance and distribution in midwater were assessed between 9 June and 7 August 2009 using acoustic-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 2009, as in the previous 3 years, compared to 2001-2005. Fewer pollock were observed east of 170° W than in 2008, and a larger percentage of those were inside the Steller sea lion Conservation Area (SCA) than outside the SCA (79% in 2009, 70% in 2008). The majority of the pollock biomass in the U.S. Exclusive Economic Zone (EEZ) was located to the west and northwest of the Pribilof Islands 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 8.08 billion fish weighing 0.924 million metric tons (t); in the Russian EEZ, there were 9.67 million fish weighing 0.005 million t (0.6% of the total midwater biomass). East of 170° W, (9.6% of total biomass) the predominant length mode was 55 cm both inside and outside of the SCA. In the U.S. west of 170° W (89.8% of total biomass) dominant modal lengths were 13, 31, and 23 cm, respectively. In Russia, modal lengths were 43, 51, and 29 cm, with proportionally more adults and fewer juveniles than in the adjacent western U.S. EEZ. Age results indicated that inside the U.S. EEZ, juvenile walleye pollock (ages-1, -2, and -3) were dominant numerically (64%, 10%, and 21%, respectively) and represented 63% of the total biomass. Adult pollock (ages 4+) totaled 6% of the population numerically and 37% of the total biomass. Vertical distribution analyses 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; 17% of juvenile biomass was within 50 m of the surface. Three-dimensional size and shape patterns of the juveniles are described using data collected with a calibrated multibeam sonar, and variability in these patterns are explored as a function of ontogeny. Finally, a new euphausiid index of abundance computed from backscatter at four frequencies (18, 38, 120, and 200 kHz) is described.