Sablefish Populations on Gulf of Alaska Seamounts
The Gulf of Alaska seamounts are a group of undersea mountains of volca-nic origin rising from the ocean floor at depths of 3,200–4,000 m to within 400–800 m of the surface (Fig.1). They are located in the eastern and central Gulf of Alaska at distances of 270–465 km offshore. Half of the major seamounts in this group fall within the U.S. Exclusive Economic Zone and half are outside; all are separated from the continental slope by waters from 2,900 to about 5,000 m in depth.
NOAA’s National Marine Fisheries Service (NMFS) first conducted exploratory fishing on nine Gulf of Alaska (GOA) seamounts in June and July 1979 (Hughes, 1981). Using trawls and traps, they found that sablefish, Anoplopoma fimbria, were the dominant finfish on each of the seamounts and that trap catch rates of sablefish were higher than those from NMFS survey sites off southeastern Alaska. There were more than twice as many males as females, and nearly all sablefish were ripe, spawning, or recently spent. However, only older and larger fish were caught on the seamounts, suggesting that the seamount populations are maintained by the migration of mature fish from the continental slope rather than by local recruitment.
Tagged sablefish released in the Bering Sea, Aleutian Islands (BSAI) region, and the western and central GOA have been recovered on GOA seamounts, verifying the occurrence of slope to seamount migration (Shaw and Parks, 1997). Of 99 tagged sablefish released on 5 GOA seamounts in 1979, 5 have been recovered on the seamount where they were tagged, and none have been recovered elsewhere.
NMFS revisited seven of the sea-mounts sampled in 1979 and one (Murray Seamount) that was not sampled in 1979. Sablefish were tagged and released on the seamounts during 1999–2002 to de-termine the extent, if any, of emigration from the seamounts back to the con-tinental slope and movement between seamounts. A second objective was to gather biological information from the seamount sablefish populations.