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PUBLISHED: 1:52 PM on Wednesday, April 5, 2006
Researchers study effects of growing crab

Laine Welch

People are already growing crops of king crab in several countries around the world. But tracking how well the home grown crabs might survive in the wild remains one of the biggest mysteries. That was just one of the fascinating findings shared by the world's foremost crab scientists future at a first of its kind gathering two weeks ago in Kodiak.

In Japan, for example, researchers ten years ago produced half a million king crab larvae in large hatchery vats. The small crabs were eventually placed in bags in the ocean to harden and after several months, they were released into the ocean. But no follow up was done, so nothing is known about their survival.

Russian researcher Nina Kovacheva of Moscow has developed a closed recirculation system for king crab that has yielded a 35 percent survival rate through the first stage of development. Her team is now raising 2,000 juvenile crabs in a 1,500 square meter pen on the sea floor (about half the size of a football field). The Russian scientists are also using a system of 42 floating tanks, each holding about 40 pounds of king crab.

Gustavo Lovrich of Argentina, who focuses on golden king crab, has discovered that good aeration and water quality are keys to their survival. Likewise, Dr. Kurt Paschke of Chile has learned that tiny golden king crabs grow best when they are raised in the dark, because they spend less energy swimming. Paschke raises his crabs in salmon egg trays using upwelling water, with densities of up to 800 crabs per tray. He has found that with good water exchange, fast growers may reach 100 millimeters in 3.5 years. Paschke hopes to soon produce over 19,000 golden crabs per year.

Closer to home, Dr. Tom Shirley at the University of Alaska/Fairbanks School of Fisheries and Ocean Sciences (Juneau campus) has discovered that golden king crabs produce eggs that are 20 times the size of red king crab, and that the newly hatched eggs contain large quantities of lipid (fats). Consequently, they don't need to feed and can live more than six months without doing so. Also in Alaska, Dr. Brad Stevens has raised several hundred red and blue king crab in PVC tubes and beakers over four years at the federal Near Island Research Facility at Kodiak. He said one of his biggest challenges is refining their diet of brine shrimp and diatoms.

Stevens credited researcher Gro van der Meeren of Norway with giving the group a "reality check." She pointed out that few crab enhancement programs have been successful due to a lack of ecological understanding. The goal is simple: to release small crabs, and allow them to grow to maturity and recapture them. She told the group that the animals must first be adapted to their new conditions in the wild. They need to be released under correct light and temperature conditions, they need to find shelter immediately, and the habitat must be appropriate. Stevens added: "We need to give hatchery raised crabs the chance to acquire adaptive behaviors by challenging them in the lab with natural habitats, foods and predators. And in order to determine the effectiveness of such a program, we need a method to mark hatchery raised crabs in order to distinguish them from wild crabs."

Stevens said it is certainly possible to enhance king crab stocks in Alaska, but it would require a large financial outlay. "I'm guessing $20 million for a facility and operating costs of $2 - $3 million a year. Those are government estimates," he said, adding that the cost would likely be far less if a project was undertaken by fishermen.

Stevens said, "If you started with 200 females, you could expect to produce 30 million larvae. Survival to the first crab stage might range from 25 to 75 percent, and survival to maturity or capture size about eight years later might range from three to 25 percent if you're lucky. At current prices, that should produce a benefit to cost ratio of from one to ten. If you're a banker and your goal is to make money, you say this is not the best investment. But if your goals are to maintain fishing opportunities, to re-establish depleted populations, to provide employment for fishermen and their offspring, to maintain the socioeconomic structures of coastal communities, and to produce a high quality seafood product then maybe it would be a good thing."

Welch, who lives in Kodiak, has written about Alaska's seafood industry since 1988.


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