The Atlantic's severely overfished populations of swordfish, shark and marlin can be restored to sustainable levels if governments strictly curtail fishing with drift longlines, according to a new study by the National Coalition for Marine Conservation. The environmental group recently completed a groundbreaking two-year study of drift longlines that explored ways to minimize the "bykill" of unwanted or prohibited fish.

Longlines -- extraordinarily long floated mainlines, often stretching more than 30 miles, from which thousands of baited hooks are suspended in the deep ocean --are commonly used to catch large, highly valuable swordfish and tuna but also catch an enormous quantity of nontargeted fish such as shark and marlin.

Virtually all species of large pelagic fish in the Atlantic are classified as overfished, including swordfish, blue and white marlin, giant bluefin tuna and a number of large coastal sharks.

In 1991, the United Nations placed a moratorium on huge drift nets. Now the NCMC is calling on governments to reduce longline bykill by 75 percent.

A comprehensive longline bycatch reduction program should include:

Establishing no-longlining zones where the bykill of protected or overfished species or age groups is highest or detrimental to their recovery, such as nursery and breeding grounds or other "hot spots."

Greatly reducing the amount of time that longline hooks are in the water to enhance the survival of fish and other animals caught incidentally.

Counting dead discards against allowable catch limits as an incentive for fishermen to fish more selectively.

Nearly one-quarter of the global catch of fish is discarded as unintended or unwanted catch because of indiscriminate fishing practices, according to the United Nations. In the U.S. drift longline fisheries for swordfish and tuna, half the catch is returned to the sea. Of this discarded "bycatch," more than half already are dead.