ANCHORAGE, Alaska (AP) — A Honolulu-based Coast Guard cutter is off the coast of Japan, pursuing prosecution of an unregistered fishing vessel suspected of catching 40 tons of fish with an illegal high seas driftnet.

Admiral Robert J. Papp, Jr., the Coast Guard commandant, on Monday announced that the 378-foot cutter Rush had been assigned to Alaska waters but had followed the fishing vessel across the Pacific to enforce commercial fishing law.

"I would call this fishing piracy that is going on," Papp said during a hearing in Kodiak by the U.S. Senate Homeland Security Appropriations Subcommittee.

"They put eight miles of net out there and collect everything that flows through it," he said, possibly picking up migratory stocks destined for Alaska waters.

Crew members from the Rush have boarded the vessel, Papp said. The Coast Guard is working with other departments on the case.

"We have something called the Maritime Operational Threat Response organization, which works across State and Justice and other departments — and we've come to a national objective of seizing this, what amounts to, we found out now, is a stateless vessel," he said.

The vessel carried Chinese citizens who were manning the vessel, Papp said, and may be passed to China for prosecution.

"As a fallback, we can bring it back to the United States for prosecution as well," he said.

U.S. Sen. Mary Landrieu, D-La., chaired the subcommittee hearing.

"I hope we're filing charges — not just against the men operating the ship, but the buyers of these fish, and tracking it down to the networks that are funding these kinds of illegal operations," Landrieu said.

David Mosely, a Coast Guard spokesman in Anchorage, would not say when or where the pursuit of the other vessel began, citing agency policy to not comment on ongoing investigations.

Paul Niemeier, who works in the International Fisheries Affairs Division of the National Oceanic and Atmospheric Administration, said Tuesday high seas driftnets have been banned internationally since 1992. In the early 1990s, hundreds of vessels were setting them, he said. Each net was an average of 30 to 60 miles long.

"Driftnets don't differentiate, don't select very well what they catch," he said by phone from Silver Spring, Md. "Anything that swims into them has a pretty good possibility of getting tangled up. So they were catching marine mammals and seabirds and sharks — anything under the sun, including the target species, which back in those days was either tuna or salmon, depending on the mesh size."

If a fish can get its head through the mesh, it will get caught behind the gill flaps, Niemeier said. Bigger species hit the net, twist and turn, and get tangled up.

"That's the way a lot of the sharks and marine mammals and seabirds used to get caught, just twisting around in the net."

The problem has dramatically declined. Just five or six years ago, he said, there were more than 100 sightings of suspected illegal fishing boats. Last year, there were two sightings. The Coast Guard seized one vessel and the other escaped.

"It's still a concern, but at least the numbers are a lot less than they used to be, and it seems like they're using smaller nets," he said. That may be because they're easier to pick up and run with, too. You don't just pick up a 30-mile net very easily."