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Marine Ecology and Stock Assessment Program

Deepwater Longline Study for Giant Grenadier and Sablefish

In August 2008, ABL used the chartered commercial longline vessel Beauty Bay to conduct a deepwater longline survey feasibility study in the western Gulf of Alaska. The objective was to investigate the abundance and biological characteristics of giant grenadier and sablefish in deep waters of the Gulf of Alaska that have not been previously sampled in fishery surveys.

Longline and trawl surveys in Alaska both indicate that these two species are by far the most abundant fish at depths 400-1,000 m on the continental slope, but their abundance in deeper water is unknown.

The study consisted of fishing five longline stations on 6-10 August east of Dutch Harbor at depths up to 1,620 m. However, due to vessel mechanical problems and the difficult fishing conditions encountered at the deep-water stations, total fishing effort in the study was roughly 40% less than had been planned, and depth coverage was also less than ideal.

The study demonstrated that fishing longlines in deep water can present special problems and that extra fishing effort may be needed to compensate for these problems. Because of the limited fishing effort and incomplete depth coverage, results of the study were not conclusive. However, catch rates of sablefish were extremely low, and those of giant grenadier were relatively high.

This suggests that biomass of sablefish at depths greater than 1,000 m in the western Gulf of Alaska is probably inconsequential, whereas considerable biomass of giant grenadier may exist at these depths. An unexpected finding of the study was the large abundance of another grenadier species, Pacific grenadier, at some of the deep-water stations. At one station, Pacific grenadier were caught on 56% of the hooks that were set.

By Dave Clausen


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