Resource Assessment and Conservation Engineering Report for Alaska Fisheries Science Center Quarterly Report for January-March 1998

Midwater Assessment and Conservation Engineering (MACE): Winter 1998 Bogoslof Survey of Spawning Walleye Pollock

Scientists in the AFSC’s Midwater Assessment and Conservation Engineering (MACE) program conducted an echo integration-trawl (EIT) survey of walleye pollock (Theragra chalcogramma) in the southeastern Aleutian Basin near Bogoslof Island 1-10 March 1998. Scientists from Korea and Japan also participated in the survey. The work was conducted aboard the NOAA Ship Miller Freeman. This was the 10th annual survey (excepting 1990) in a series that began in 1988 with the objective of assessing the population distribution and abundance of spawning pollock in this region. The survey area extended from approximately long. 166°00’W to long. 170°20’W and from the Aleutian Island chain to 20-80 nmi offshore. Acoustic data were collected along a trackline consisting of 27 transects spaced at 10 nmi east of long. 167°10’W and 5 nmi to the west. Fourteen midwater trawl hauls were made to sample echosign and provide biological data on spawning pollock. The geographic distribution of pollock was similar to that observed in 1996 and 1997. Approximately 70% of the biomass was located in the off-shelf waters between the Islands of Four Mountains and the west end of Umnak Island. The majority of the fish encountered were in prespawning condition. Lengths ranged from 34 to 66 cm with a major mode at 54 cm, and fish less than 48 cm comprised 17% of the surveyed population. Preliminary analyses resulted in a biomass estimate of 0.5 million metric tons.

By Taina Honkalehto.

Winter 1998 Shelikof Strait Survey of Spawning Walleye Pollock

An EIT survey to assess the distribution and abundance of spawning walleye pollock within Shelikof Strait was conducted between Chirikof Island and Cape Chiniak during 11-25 March 1998. This is the 17th annual spawning stock survey of walleye pollock in the Shelikof Strait area since 1980 (no survey in 1982). A total of 1,800 nmi of transect trackline and 31 hauls were completed during the survey. As in previous years, most spawning pollock were distributed along the western side of the strait with greatest densities near Capes Kekurnoi and Kuliak. Fish were most abundant within 50-150 m of the bottom. The size distributions of pollock from hauls within the strait generally exhibited dominant modes around either 30-39 cm or 50-60 cm FL. Sixty percent of the females greater than 34 cm FL were in either prespawning or spawning condition and only 9% were spent. Pollock from the 1994 year class (30-39 cm FL mode) formed a strong, well-defined midwater layer (150-200 m depth) that was broadly distributed from about Uyak Bay south to Sitkinak Strait. The areal extent and strength of this layer of 4-year-old fish supports earlier EIT survey observations that the 1994 year class is relatively strong.

By Michael Guttormsen.

Resource Assessment & Conservation Engineering

Resource Assessment &
Conservation Engineering