Resource Assessment & Conservation Engineering (RACE) Division

Groundfish Assessment Program

2005 Gulf of Alaska Biennial Groundfish Assessment Survey Completed

The fourth in the series of biennial bottom trawl surveys of Gulf of Alaska (GOA) groundfish resources was conducted from 18 May through 6 August 2005. Prior to establishing a biennial schedule in 1999, groundfish resources in the GOA had been surveyed by the RACE Division triennially beginning in 1984. The GOA triennial surveys covered the continental shelf (out to 500-m depth), but only included portions of the continental slope in 1984 (to 825 m) and 1987 (to 750 m). The GOA survey has been repeated on a biennial schedule since 1999. The biennial surveys were designed to cover the continental shelf and slope between the Islands of the Four Mountains (long. 170°W) and Dixon Entrance (U.S.-Canada border in Southeast Alaska) out to the 1,000 m depth contour.

While the 1999 survey succeeded in sampling the entire area, the 2001 survey area was reduced because the Division's survey responsibilities were stretched across three major areas that year under limited funding. Consequently, the 2001 survey area did not include the area east of long. 147°W, nor did it extend deeper than 500 m. The 2003 survey covered the entire geographic range, but vessels were only capable of sampling to depths of 700 m. This year the survey covered the entire geographic and depth extent of the survey area.

Sampling was conducted aboard three chartered commercial trawlers: the Gladiator, which worked for 65 days between 18 May and 21 July, and the Sea Storm and the Northwest Explorer, which each worked 80 days between 18 May and 6 August. The survey period was divided into four legs of approximately 20 days each (the Gladiator’s cruise ran for three legs lasting about 22 days each). Sampling began near the Islands of Four Mountains and progressed eastward on the continental shelf and slope to the U.S.-Canada border in Southeast Alaska. Originally, 777 stations were allocated among 54 depth and geographic strata and were preselected randomly from a grid of potential sites overlaying the survey area. If rugged bottom or heavy commercial fishing prevented sampling a station, a nearby alternate station was selected. By early July it became apparent that the vessels were significantly ahead of schedule. Another 109 stations were allocated to strata east of long. 154°W and most of these were also completed by the end of the survey. Of the 905 attempted standard survey tows, 839 were successfully completed, ranging in depth from 22 to 882 m.

The primary focus of the biennial groundfish surveys is to build a standardized time series of data designed to assess, describe, and monitor the distribution, abundance, and biological condition of various GOA groundfish stocks. Specific objectives of the 2005 survey, as in others preceding it, were to

1. Define the distribution and relative abundance of the principal groundfish and invertebrate species inhabiting the continental shelf and slope of the GOA.
   
2. Collect data to define various biological characteristics of major groundfish species, such as age, sex, size, growth rates, length-weight relationships, and feeding habits.
   
3. Collect integrated fishing performance, net configuration, and position data for all trawl hauls with which to derive precise effort estimates.
   
4. Collect environmental data such as surface-to-bottom water column temperatures.
   
5. Collect biological specimens and data requested by scientists from the AFSC or other cooperating research groups.

Preliminary results have been analyzed from the survey data and estimates of abundance and size composition have been turned over to stock assessment authors. Results will be finalized soon following further examination of the effort data for each tow.

Over the entire survey area, the most abundant species in 2005 were, in order, arrowtooth flounder, Pacific ocean perch, giant grenadier, Pacific halibut, walleye pollock, northern rockfish, and Pacific cod. We can compare the 2005 abundance estimates with the 2003 results in all areas and in all depths except the deepest (700 – 1,000 m) depth stratum.

Since 2003, increases in the estimated abundance were seen for Pacific ocean perch, by 68% to 766,400 t; northern rockfish, by over 400% to 359,000 t; giant grenadier, by 48% to 587,000 t; and Pacific cod, by 4% to 308,000 t.

Reduced biomass estimates were seen for arrowtooth flounder, by 33% to 1,900,000 t; halibut, by 11% to 565,000 t; and pollock, by 11% to 378,000 t.

By Mark Wilkins


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AFSC Quarterly
Research Reports July-Sept 2005