Damage and disturbance to coral and sponge habitat of the Aleutian Archipelago

Abstract

Video imagery was examined to quantify seafloor disturbance and damage to corals and sponges relative to fishing practices in the central Aleutian Islands of Alaska. Corals and sponges were classified as damaged if they had broken skeletons, missing or broken branches, were torn (i.e. sponges) or detached from the seafloor, or were attached but lying on the seafloor. Disturbance was defined as any alteration to the seafloor or biota caused by fishing gear or natural events. Overall, 14% of corals and 21% of sponges were damaged, and disturbance was widespread and evident on most video transects. The proportion of damaged corals was significantly less (p = 0.003) in areas with little or no bottom trawl fishing versus areas with medium and high intensity bottom trawl fish- ing. For other gear types, damage was not significantly different among fishing levels. Damage for all corals was 7% in untrawled areas, 7% in low-intensity areas, 14% in medium-intensity areas, and 49% in high-intensity areas. For gorgonians, 5% were damaged in untrawled areas and 23% were damaged in high-intensity areas. For hydrocorals, damage was 10% in untrawled areas and 53% in medium-intensity areas. Hydrocorals were absent from high-intensity areas. About 40% of sea whips were damaged in high-intensity areas versus 1% in other areas. While some protective measures have been implemented to halt the expansion of bottom trawl fishing to unfished areas, the con- servation of coral and sponge habitat in fished areas is still of primary concern.