| Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska (DY1706, ME70). The
Midwater Assessment and Conservation Engineering (MACE) program of NOAA Fisheries,
Alaska Fisheries Science Center (AFSC) conducted an acoustic-trawl (AT) stock assessment
survey along the Gulf of Alaska (GOA) shelf and associated bays during the late spring
and summer of 2017 to estimate the distribution and abundance of walleye pollock (Gadus
chalcogrammus). The survey was conducted 9 June-16 August aboard NOAA Ship Oscar Dyson,
a 64 meter stern trawler equipped with acoustic and oceanographic instrumentation.
The primary instrument for the survey was a Simrad EK60 split-beam echosounder system
utilizing five frequencies (18, 38, 70, 120, and 200 kHz). A Simrad ME70 multibeam
echosounder system was used during nighttime operations to evaluate the topography
of the seafloor in various habitats for select (typically untrawable) areas. The vessel
departed Kodiak, Alaska on 9 June and conducted the survey in three legs with all
port calls in Kodiak; the project was completed with the arrival of the vessel in
Kodiak on 16 August. Leg 1 of the project was conducted 9-28 June along the Gulf of
Alaska (GOA) shelf from the Islands of Four Mountains to Outer Shumagin Trough (12-18,
20-21, 22, and 26-27 June). Leg 1 survey areas included Sanak Trough (19 June), Morzhovoi
Bay (19-20 June), Pavlof Bay (21 June), Shumagin Islands area (23-25 and 26 June),
and Mitrofania area (25 June); the vessel transited to Kodiak 27-28 June. The vessel
departed Kodiak on 3 July to start leg 2 (3-28 July) and conducted survey work in
Shelikof Strait (3-8 and 10 July), Nakchamik area (9 July), Alitak Bay (12-13 July),
initial survey of Barnabas Trough (14-15 July), and GOA shelf (9-10, 10-12, and July).
The vessel returned to Kodiak on 15 July, ending leg 2, due to mechanical issues and
departed Kodak on 28 July to start leg 3. Leg 3 work included surveys of Chiniak Trough
(28-29 July), Barnabas Trough (31 July-1 August), Marmot Bay (3-4 August), and completion
of GOA shelf work (3 July; 2 and 4-14 August). The vessel transited to Kodiak Island
(14-15 August) and ended the project in Kodiak on 16 August. Sphere calibrations of
the EK60 and ME70 echosounder systems were conducted in Kalsin Bay, Kodiak Island,
Alaska on 9 June with an additional EK60 calibration conducted at the end of the project
on 16 August. Small surveys were conducted on select untrawlable habitat areas throughout
the project using a Simrad ME70 multibeam echosounder system. |