Bottom Trawling Fact Sheet

Aleutian Corals Being Destroyed

In July 2002, scientists discovered deep-sea coral reefs in state waters off the Aleutians containing over one hundred species of coral and sponge, comparable in size and structure to tropical coral reefs. The Aleutian Islands marine ecosystem is an exceptional area of biological productivity and diversity in part because of its complex seafloor habitat. As a result of bottom trawling in these areas, critical fish habitat in Alaska state waters is currently being destroyed and will not recover for centuries if ever.

Major commercial species that use these habitats include Atka mackerel, Pacific cod, golden king crab, Pacific ocean perch, several other species of rockfish, walleye pollock, Greenland turbot, greenling, shrimp, and other flatfish, octopus, and shrimp (see Table 1). Scientific studies of coral in Alaska have concluded that corals are important components of the deepwater ecosystem and removal of these slow-growing corals could cause long-term changes. (Krieger and Wing 2002).

Bottom Trawling Kills

A report issued by the National Academy of Sciences, titled “Effects of Bottom Trawling and Dredging on Seafloor Habitats,” was released on March 19, 2002. The report says that bottom trawling is killing vast numbers of marine animals.

Scientific Research and Information Documenting Bottom Trawling in Alaska

Bottom trawling is the most destructive fishing gear type recorded and reported on coral and sponge in Alaska, effectively clearcutting large areas of coral and sponge habitat. This gear type is responsible for 97% of the total reported bycatch of coral and sponge in Alaska (NMFS 2001).

Destructive Fishing Practices Impact on Coral and Sponge Habitats

The areas in Alaska that are the most at risk of coral and sponge destruction are the waters surrounding the Aleutian archipelago, which have minimal protection from bottom fishing and at the same time, the greatest diversity and abundance of coral in Alaska (Heifetz 2000). Recent studies have shown that bottom fishing has a substantial impact on deep sea corals and sponges in Alaska and worldwide.

1. On a research cruise to the Aleutians this year, NMFS scientists Bob Stone and Jon Heifetz discovered coral and sponge bioherms. These scientists witnessed heavily trawled areas devoid of corals and sponge and parts of the bioherms with large tracts of crushed corals and sponges (Stone and Heifetz, pers. comm. 2002; O’Harra 2002).
2. Krieger (2001) found that a 1990 research trawl in the Gulf of Alaska removed one ton of corals and left 27% of corals detached in its net path. 84% of detached corals remained in the net. No young corals had repopulated the damaged colonies after 7 years.
3. Heifetz (1999 in NPFMC) found that boulders were displaced, and large epifaunal invertebrates were removed or damaged by a single pass of a research trawl. Over 50% of the vase sponges and sea whips encountered by the gear were damaged. Of the 51 individual rockfish observed in the study, 39 were associated with Primnoa.
4. Freese et al. (1999) found that a single pass of a bottom trawl in the Gulf of Alaska removed or damaged 70% of vase sponges, 55% of sea whips, over 20% of brittle stars, and 13% of finger sponges.
5. In Seguam Pass in the Aleutian Islands, gorgonian corals, which 20 years ago were a major component of the bycatch of the Atka mackerel fishery, are now caught infrequently (NMFS 2001). This suggests that after years of bottom fishing, most of these habitat-forming species are gone.
6. McConnaughey et al. (2000) compared heavily fished to unfished seafloor in the eastern Bering Sea and concluded that long-lived, slow-growing taxa were significantly more patchy in highly fished areas, suggesting a slow recovery process.
7. High (1998) found in Southeast Alaska that longlines affect the sea floor by snagging objects in its path, including rocks and corals, breaking hard corals. When hooked fish try to escape, motion of the line was noted for distances of 50 feet or more on either side of the hooked fish.