DY1207 Bering Sea ME70 |
Scientists from the Midwater Assessment and Conservation Engineering (MACE) Program
of the Alaska Fisheries Science Center (AFSC) have conducted summer surveys to estimate
the abundance and distribution of walleye pollock (Theragra chalcogramma) on the eastern
Bering Sea (EBS) shelf since 1979. Surveys have been conducted either annually or
biennially since 1994. The 2012 acoustic-trawl (AT) survey was carried out between
7 June and 10 August aboard the NOAA ship Oscar Dyson. Its primary objective was to
collect acoustic and trawl information to estimate walleye pollock midwater abundance
and distribution on the U.S. and Russian Bering Sea shelf. Additional survey sampling
included conductivity-temperature-depth (CTD) and expendable bathythermograph (XBT)
casts to characterize the Bering Sea shelf physical environment, and supplemental
trawls to improve acoustic species classification and to obtain an index of euphausiid
abundance using multiple frequency techniques. A number of specialized sampling devices
were used during the survey, including light level sensors; a Simrad ME70 multibeam
sonar to image fish schools; an 83-112 bottom trawl modified to sample fish in midwater;
a trawl-mounted stereo camera ("Cam-Trawl") designed to identify species and determine
size and density of animals as they pass by the camera during a haul, and a small,
bottom-moored, trigger camera system to autonomously collect images of fish on the
seafloor. |
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