Longline tuna fishing expeditions inadvertently hooked or entangled 11 whales and one dolphin off Hawaii last year, according to the latest federal data.

But the actual bycatch was likely several times higher because the figures reflect only incidents recorded by National Marine Fisheries Service observers aboard longline fishing boats.

Last year, observers were aboard just 285, or slightly more than 20 percent, of the 1,314 trips made by Hawaii-based open-ocean longline fishery vessels.

A spotted dolphin died.

The 11 whales were injured, including two false killer whales, and released.

Longline fishing vessels string a line in the ocean, ranging from 1 mile to 50 miles long, to catch fish. They run smaller lines with baited hooks off the central line and wait for bait to attract fish.

Bill Robinson, the National Marine Fisheries Service's regional administrator for the Pacific islands region, said recently that the Hawaii longline tuna fishing industry's marine mammal bycatch was stable and not increasing dramatically.

Still, he said incidents of the fishery's interaction with marine mammals were high enough to be of concern.

This is especially true because some scientific studies say the false killer whale population just off Hawaii waters is unique and distinct from the open-ocean-dwelling false killer whale population. The Hawaii group is also small, numbering perhaps around 100 individuals.

“;Of course, the smaller the population, the more concern there is that the impacts would have some effect,”; Robinson said.

The agency is working with the fishing industry and the Western Pacific Regional Fishery Management Council to come up with ways to reduce the impact longline fishing has on marine mammals, Robinson said.

In 2007, Hawaii-based longline tuna vessels accidentally caught seven whales and one dolphin. The whales included four false killer whales.

Mike Milne, an activist with Forest Knolls, Calif.-based Sea Turtle Restoration Project, said the government should have more observers on the longline tuna fishery boats.

All longline swordfish boats, he noted, have observers on board.

“;We have a fishery that's interacting with what looks like quite a few marine mammals,”; Milne said. “;We'd like to see more observers on these boats.”;

Regulators have had more success limiting the accidental capture of sea turtles and seabirds.

Longline fishing vessels must use large circle hooks, set their lines at night instead of during the day and use fish bait instead of squid.

These rules have helped reduce the sea turtle and seabird bycatch rate by 90 percent compared with before 2000, Robinson said.