A network of nine protected areas along the West Hawaii coastline is nurturing new generations of yellow tang to stock local reefs and aquariums around the world.

Yellow tangs represent more than 80 percent of the region's aquarium catch, with collectors each year removing at least 280,000 specimens valued in total at $1 million.

Long-standing conflicts between dive tour operators and aquarium fishers led to a 1998 state law mandating designation of 30 percent of West Hawaii's coastal waters as fish replenishment areas where tropical fish collecting is banned. A community group, the West Hawaii Fisheries Council, developed a plan for a string of reserves that comprise 28 percent of the coastline. Including existing reserves, a total of 35 percent of the 150-mile Kona and Kohala coastline is closed to aquarium collecting.

The yellow tang fishery is unique because juveniles 2 to 4 inches in length are most desired and the adults aren't fished, said marine biologist Jeremy Claisse, a former University of Hawaii researcher now with Occidental College in Los Angeles.

Before the protected zones were established, population densities of juveniles were similar in open waters and at sites due to become fish replenishment areas, according to a study by Claisse and other researchers. In both areas, densities were half what they were in established reserves.

Ongoing monitoring by researchers with the state Division of Aquatic Resources, the University of Hawaii-Hilo and Washington State University at Vancouver showed that by 2008, juvenile yellow tang population densities in the protected zones were nearly seven times as abundant as in the open areas.

"You get more bang for your buck with the protected areas because yellow tang adults are not targeted by the fishery in the open areas," Claisse said. "So once the juveniles grow up and become adults, they can move out into surrounding open areas, where they can live a long time, reproducing year after year."

He said the study found evidence of this "spillover" effect in population densities of adult tang, which can live 40 years and longer. Densities were highest within the reserves and in adjacent boundary areas up to a half-mile or more away, and lowest in open areas far from the protected sites.

Yellow tang are "broadcast" spawners, meaning males and females just spray their eggs and sperm out into the water during spawning. The fertilized eggs typically float offshore and hatch into larvae after a few days. The larvae spend two months trying to survive in the open water before settling in nearshore coral reefs as juveniles. During the juvenile stage, the fish pretty much just stay in one location for the next few years.

How many larvae survive from year to year varies based on the amount of available food, predation and ocean currents. Claisse said fewer than one-tenth of 1 percent make it back to the reef, and research on juvenile survival has found that only about 1 percent of new reef recruits survive to become adults at age 5 that start spawning.

With such poor survival odds, Claisse said it's vital to build up the adult population as much as possible to ensure the best chances of recruitment from year to year.

"As long as the protected areas continue to increase the adult population, that will lead to sustainability. Since the protected areas went into effect, the catch has doubled and the number of fishermen reporting catches also has gone up," Claisse said.

The number of West Hawaii aquarium collecting permits doubled from 36 to 72 between 1999 and 2007, with "active" collectors — those taking 1,000 or more fish annually — jumping from 16 to 37 during that same period, according to the state Division of Aquatic Resources.

Some fishers downplay the spillover effect, saying it will not be as far-ranging as expected.

"Marine fish do not migrate out as much as first thought," said Ron Tubbs, who owns RT Distributors in Waimänalo and Kona, a supplier of saltwater aquarium fish. "Tropical fish collectors were told 30 percent closures would increase adjacent areas' fish counts by 30 percent. Some fish do spread into the nonclosed areas but not as much as what was first thought. The scientific basis for the 30 percent closures is in question."

Tubbs worries that closing off 30 percent of West Hawaii's coastal waters could cause open areas to be overfished, and that an overabundance of yellow tang in closed areas may be crowding out rarer species. "If you close large areas, fishermen are forced into smaller areas, which see an increased impact. Right now, research and fish counts show tropical fish collectors are sustainable," he said.

Tubbs said he would like to see the existing fish replenishment areas replaced with numerous smaller preserves, "which would both replenish open areas and preserve representative ecosystems."

Tropical fish collector David Dart of Kailua, Kona, agrees some of the replenishment areas are too big and said the spots picked for protection were selected based on where user conflicts were occurring. He said he would like to see scientific data used as a basis for any further action on reserves.

"Overall it's been successful in the respect that it's kept the people with conflicts away from each other, and the fish count in the FRAs and along the whole coastline is generally better now than 10 years ago," he said.

"The good thing about the FRAs is that you're always going to have a healthy population along the reef that can swim out everywhere else."

Dart said the aquarium fishery is experiencing a particularly good year. "It depends heavily on the currents and where the (larvae) drop happens. It's absolutely amazing when you have a good drop how many fish there actually are," he said.

Resource managers, conservationists and ocean users said the fish replenishment areas wouldn't be nearly as effective if aquarium collectors, dive companies and community members hadn't participated in the process of establishing the network.

Bill Walsh, an aquatic biologist with the Division of Aquatic Resources who works on the Kona Coast, said the West Hawaii Fishery Council is discussing ways to improve management of the fishery, including allowing flexibility in closing areas in response to public concerns while opening up a similarly sized space to maintain the mandated proportion of reserves, and creating a list of species approved for the aquarium trade and a limited list of "species of special concern" off-limits to all fishers.