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Marine Ecology and Stock Assessment Program

2009 Sablefish Longline Survey

The AFSC has conducted an annual longline survey of sablefish and other groundfish in Alaska from 1987 to 2009. The survey is a joint effort involving the AFSC's Auke Bay Laboratories and Resource Assessment and Conservation Engineering (RACE) Division. It replicates as closely as practical the Japan-U.S. cooperative longline survey conducted from 1978 to 1994 and also samples gullies not sampled during the cooperative longline survey.

In 2009, the thirty-first annual longline survey of the upper continental slope of the Gulf of Alaska and eastern Bering Sea was conducted. One hundred-fifty-two longline hauls (sets) were completed during 30 May 26 August 2009 by the chartered fishing vessel Ocean Prowler. Sixteen kilometers of groundline were set each day, containing 7,200 hooks baited with squid.

Sablefish (Anoplopoma fimbria) was the most frequently caught species, followed by giant grenadier (Albatrossia pectoralis), shortspine thornyhead (Sebastolobus alascanus), arrowtooth flounder (Atheresthes stomias), and Pacific cod (Gadus macrocephalus).

A total of 74,444 sablefish were caught during the survey. Sablefish, shortspine thornyhead, Greenland turbot (Reinhardtius hippoglossoides), and lingcod (Ophiodon elongatus), were tagged and released during the survey. Length-weight data and otoliths were collected from 1,860 sablefish.

Killer whales (Orcinus orca) took fish from the longline at 10 stations in the Bering Sea region, 2 stations in the western Gulf of Alaska, and 1 station in the central Gulf of Alaska. This was the highest killer whale depredation in the survey ever observed in the Bering Sea and severely affected catches in this region.

Sperm whales (Physeter macrocephalus) were often present during haul back and were observed depredating on longlines at five stations in the eastern Gulf and five stations in the central Gulf of Alaska. These numbers represent a high incidence of sperm whale interactions in the central Gulf, but the number observed in the eastern Gulf was much lower than that experienced in 2008.

Several special projects were conducted during the 2009 longline survey. Lingcod were tagged with archival temperature/depth tags in the West Yakutat and central Gulf of Alaska regions. Photographs of sperm whales observed during the survey were taken for contribution to the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) sperm whale catalog.

A NOAA Hollings Scholar intern conducted a hooking injury project for sablefish. During this project, tagged sablefish were examined for prior hooking injuries and injury location and severity were recorded. This information, along with data from a previous tagging study, will be used to help understand mortality that occurs as a result of hooking injury.

A 2-day experiment was conducted near Yakutat on 21-22 July to test new methods for quantifying sperm whale depredation rates. Acoustic recorders were deployed during survey operations to passively collect the acoustic recording of sperm whale sounds during gear retrieval.

Sperm whales use echolocation signals for navigation and detecting objects underwater. A "creak" is a rapid series of clicks in short succession which may indicate that a whale is homing in on a prey item. Enumerating the number of "creaks" that occur during hauling operations may provide a quantitative means of evaluating sperm whale depredation on the longline catches.

By Chris Lunsford

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