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Marine Ecology & Stock Assessment Program

Deep-sea Coral Distribution and Habitat in the Aleutian Archipelago

rockfish amongst coral
A rockfish hides amongst a dense bed of hydrocorals, demosponges, hydroids, and actiniarians at a depth of 210 m in the central Aleutian Islands.
Photo by Robert Stone.
 

Coral abundance in the Aleutian Islands far exceeds that reported for other high latitude areas of the world, and there are many endemic species.

Research conducted by ABL staff in collaboration with the Alaska Department of Fish and Game and the University of Alaska Fairbanks on deep-sea coral distribution and habitat in the Aleutian Archipelago has provided an opportunity to further our knowledge about coral and sponge ecology, taxonomy, fishing gear impacts, importance to commercial species, and habitat requirements.

The impetus for this study stemmed from the need to collect information for making fishery management decisions to protect coral and sponge habitats.

Multibeam habitat mapping of 17 sites covering 2,600 km2 at depths of 30 3,800 m coupled with in situ observations to 2,950 m from 2003 to 2004 were used to collect biological information and develop predictive models that relate coral and sponge distribution to environmental characteristics. Habitats dominated by bedrock and cobble supported the highest densities of corals. Diversity of corals and sponges increased from deep to shallow water.

For the predictive model, depth and slope were the most important explanatory variables. Models of coral and sponge presence/absence north of the Aleutian Islands Archipelago were more successful than models south of the archipelago. The most observed damage and disturbance to coral and sponge communities occurred at depths less than 800 m, which generally corresponded to the depth limit of the majority of fisheries that use bottom contact gear. There was a consistent positive relationship between damage and disturbance levels and intensity of bottom trawling, whereas results varied for other gear types.

Some commercial fish and crab species aggregate in habitats where corals are abundant, making these habitats at risk to fishing gear impacts. Protective measures implemented in the Aleutian Islands include restricting bottom trawling to historically fished areas. While this protective measure may halt the expansion of bottom trawling to areas not fished, the conservation of coral and sponge habitat in fished areas is still of primary concern.

By Jon Heifetz
 

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