i
Results of the acoustic-trawl survey of walleye pollock (Gadus chalcogrammus) on the U.S. Bering Sea Shelf in June-August 2018 (DY1807)
-
2020
-
-
Series: AFSC processed report ; 2020-07
[PDF-6.48 MB]
Details:
-
Personal Author:
-
Corporate Authors:
-
NOAA Program & Office:
-
Description:Eastern Bering Sea shelf walleye pollock (Gadus chalcogrammus) midwater abundance and distribution were assessed from Bristol Bay to the U.S.-Russia Convention Line from 6 June to 26 August 2018 using acoustic-trawl (AT) survey methods aboard the NOAA ship Oscar Dyson. In addition to surveying the traditional (core) survey area, we also surveyed a region northeast of St. Matthew (the northern extension). Water column temperatures were cooler in 2018 (mean sea surface temperature (SST) 8.5 °C, bottom temperature 3.7 °C) compared with temperatures during the previous AT survey in 2016 (mean SST 11.4°C, bottom temperature 3.9 °C), but still much warmer than in prior cold years (2006-2014; SST means between 4.9° and 6.8 °C). Walleye pollock biomass was concentrated in the regions north of Pribilof and Zhemchug canyons, and east of Pervenets Canyon, primarily between the 100- and 200-m isobaths. The estimated amount of pollock in midwater (between 16 m from the sea surface and 0.5 m off the sea floor) in the U.S. EEZ core survey area was 5.57 billion fish with a biomass of 2.50 million metric tons (t), less than half of the 2016 estimate of 12.2 billion fish with a biomass of 4.83 million metric tons. This estimate includes the lower water column (3 m to 0.5 m), estimated by combining acoustic and bottom trawl data and previously reported separately. Pollock east of 170° W numbered 1.28 billion fish and weighed 0.74 million t (27% of the total shelf-wide biomass, including the northern extension which represented 9% of shelf-wide biomass). Five- and 6-year-old pollock (43 and 45 cm mean fork lengths (FL), respectively) together composed 77.6% of the biomass east of 170° W. Pollock abundance west of 170° W was 4.29 billion fish weighing 1.75 million t (64% of total shelf-wide biomass). These estimates include an ‘unsampled’ portion of the core area (the three westernmost transects, comprising 6.1% of the core area) which was not surveyed due to ship motor failure. Most pollock west of 170° W were aged 5 and 6 years (42 and 44 cm mean FLs, respectively). The mean biomass-weighted depth of adult pollock (≥ 30 cm FL, age-3+) was 79 m in the region east of 170° W and 97 m west of 170° W. The mean weighted depth of juveniles (< 30 cm FL, ages 1 and 2) west of 170° W (relatively few juveniles were observed east of 170° W) was 106 m, 9 m deeper than adults (97 m). The mean euphausiid abundance estimate for 2018 was similar to that in 2004, a relatively low year in the index.
-
Keywords:
-
Series:
-
DOI:
-
Document Type:
-
Place as Subject:
-
Rights Information:Public Domain
-
Compliance:Submitted
-
Main Document Checksum:
-
Download URL:
-
File Type:
