Some of the most prized shrimp on sushi in Japan comes from Hawai'i.

But it doesn't come often, because the stocks of the deepwater shrimp Heterocarpus laevigatus are fished so hard that the fishery collapses in a season or two, and takes as much as three to five years to recover.

Stocks have built up since heavy fishing in 1998 and are believed to be at a peak now, and at least two big shrimp boats have arrived from the Mainland during the past four months to take advantage of that.

"The resource is thin. You catch them and then you move on," said Jim Cook, co-owner of the fishery supply firm Pacific Ocean Producers and a longtime member of the Western Pacific Regional Fishery Management Council.

The animals are known as smooth nylon shrimp, although some local fishermen simply call them sweet shrimp.

"It's the best crustacean you can have. It just has a very tender, moist texture to it," said angler Greg Holzman.

State saltwater shrimp landing records clearly show the fishery's ups and down.

The peak years — during which between 140,000 and 275,000 pounds of shrimp were landed annually — occurred in 1983 and 1984, 1989 and 1990, and again in 1998. Intervening years show only a fraction of that level of catch.

"The nature of the fishery is that it gets fished down and then the small ones that are left aren't marketable," said Mark Mitsuyasu, fishery program officer at the fisheries council.

"Traditionally, the fishery is boom and bust, and it's a five-year cycle before they get big enough to be fished again."

It has been seven years since the last boom, and Hawai'i bottomfishers report they have come across shrimpers in Hawai'i waters once more.

"Earlier this year, someone from the West Coast called to say they would like to revive the shrimp fishery," said Alvin Katekaru, assistant regional administrator for sustainable fisheries at NOAA Fisheries.

One Seattle shrimp boat arrived in March and its captain and crew were issued state commercial fishing licenses, and a second boat, reportedly from Alaska, arrived and was licensed last month.

The shrimp boats are required by state law to report their catch, but because there are only two of them, their catch will not be reported publicly to protect the confidentiality of their individual operations, said Reginald Kokubun, statistician for the state Division of Aquatic Resources.

The data will be shared with federal fisheries officials, however, he said.

At least some of the catch is reportedly being frozen on board, then boxed and shipped directly to Japan for use on sushi. Kokubun said he has received no reports that the shrimp were being sold through local dealers.

While the boats must report their catch, there is no state or federal regulatory mechanism to protect the shrimp fishery from overfishing.

Also, there is no mechanism to keep track of what other marine life is being brought up in the shrimp traps and then dumped.

"Nobody's monitoring, and you wonder what the bycatch is," said Chris Kelley, a marine biologist with the UH's Hawai'i Undersea Research Laboratory.

Fisheries researchers had high hopes for the shrimp in Hawai'i in the late 1970s and early '80s, after calculating that the potential catch could be huge — hundreds of tons each year.

It turned out those calculations were based on catch rates of another species in the continental waters off Chile, and that they were unrealistically optimistic for the narrow habitat zones around Hawaiian waters.

"If you're fishing the seamounts, you've got very limited habitat," said Paul Dalzell, a researcher with the Western Pacific Regional Fishery Management Council.

A small Hawai'i shrimping fleet developed in 1983 and '84, but collapsed within two years because of a variety of problems, including high operating costs, but also "stock depletion," according to a NOAA fisheries report.

That fishery reported 275,000 pounds of shrimp in 1984 — the highest take ever. The next year, the total report was for less than 2,000 pounds.

Since then, the major players in the occasional shrimp fishery tend to be boats from the West Coast or Alaska that hit the Hawai'i stocks until they're uneconomical, and then return to their home waters.

"It's a very intermittent fishery, but clearly it must be worthwhile for these guys to come all this way and do that," Dalzell said.

Kelley said the prized Heterocarpus laevigatus shrimp tend to be found deeper than the most prized Hawaiian bottomfish, like the snappers (onaga) and 'opakapaka, and the catching of the shrimp probably does not impact bottomfish or other fisheries.

Some of the shrimp can be caught inside the three-mile limit, which is Hawai'i state waters, and some outside that limit, which is under federal control.

Shrimpers use traps, setting dozens of them at a time in water.

The shrimp are caught in water 1,200 to 2,000 feet deep, on the underwater slopes around the island, and on pinnacles and seamounts that rise from the deep ocean to those depths.

A federal fisheries survey conducted during the 1980s calculated that at the average catch size, there are about 14 shrimp to the pound.

During the 1998 peak, the state Division of Aquatic Resources estimated the value of the saltwater shrimp at between $7 and $8 a pound, more than any other commercially fished marine species at that time, including lobster.

At that year's 176,000-pound reported take, the fishery was worth more than $1.3 million.

It is not clear whether a locally based, sustainable fishery could be established for the shrimp.

"We don't regulate that species, and we don't know much about it," Dalzell said.

He conceded that there is a gap in the regulations when it comes to shrimp.

They are not included in the agency's crustacean management plan, so there is no federal oversight.

"It may be time for the (fishery) council to take this up. My personal view is that if you're fishing commercially in federal waters, you should come under federal jurisdiction — you should have a federal permit and report your catch," Dalzell said.