Shellfish growers meet acidic water challenge

FISHERIESDecember 17, 2011 

West Coast shellfish growers have learned to save the lives of their bivalve stocks by working around the upwelling of increasingly corrosive sea water.

Higher levels of carbon dioxide (CO2) in the atmosphere are changing the chemistry of the oceans, making it more acid. The CO2 surge stems mostly from coal and, to a lesser degree, oil-fired power plants. The acidity reduces carbonate, the mineral building block of shells, skeletons and corals.

In 2005, oystermen first noticed failures in larvae production in Willipa Bay in southern Puget Sound, followed by failures at two of four of the region's major shellfish hatcheries.

"In 2008 our oyster larvae production was off 60 percent, and 80 percent in 2009," said Bill Dewey, director of public policy and communications for Taylor Shellfish Farms in Shelton, Wash., the nation's largest producer of farmed oysters, clams, mussels and geoducks.

At first, growers believed the killer was a lethal, naturally occurring bacterium, but expensive filtration did nothing to stop the larval die-offs. Then ocean acidification blipped onto the radar screen, Dewey said, and new testing equipment proved that it was the culprit.

Growers credit Washington Sen. Maria Cantwell for acting fast to get money for monitoring equipment to help the $110 million industry adapt to the corrosive sea water.

Wind direction provides the biggest warning of when to plug intake pipes to the shellfish holding tanks. At the Whiskey Creek Hatchery, for example, growers have learned that when the wind shifts from the south to the north, they have 24 hours before corrosive water shows up at their intake pipes. Other growers have learned to fill shellfish tanks late in the day instead of mornings and to use water intakes at different depths.

Meanwhile, early detection and gentle south winds have allowed Taylor Shellfish to rebound to record production of oyster larvae this year.

"I think we will survive and figure out a way through this," Dewey said. "But I don't think it bodes well for other species in the ocean and fishing interests that rely totally on natural production."

Understanding the effects of ocean acidification on food webs and ecosystems is a focus of Dr. Robert Foy, director of the NOAA Fisheries Science Center at Kodiak. He points to tiny, snail-like pteropods, which comprise nearly half the diet for pink salmon.

"Their physiology will be affected; they're not going to be able to grow," Foy said. "A 10 percent drop in pteropod production would lead to about a 20 percent drop in pink salmon body weight. The loss of that diet source would be extremely detrimental to pink salmon populations."

Catch stats shuffle

Alaska's 2012 groundfish quotas show some unexpected increases. The quotas were decided last week by the North Pacific Fishery Management Council, which oversees fishing in the federal waters from 3 to 200 miles offshore. Groundfish catches make up more than 80 percent of Alaska's total fish landings each year.

Notably, Gulf of Alaska fishermen who were bracing for a decrease in sablefish (black cod) instead got a nearly 15 percent increase, to 28.5 million pounds. It was likewise for Gulf P-cod (Pacific cod, also called gray cod or true cod). The catch was expected to tumble a bit but instead increased by 1 percent to 145 million pounds.

Also in the Gulf, pollock catches next year were bumped up 21 percent to 256 million pounds.

The story isn't quite so rosy for the Bering Sea, where some stocks are cycling downward. For sablefish, the 2012 catch was trimmed nearly 10 percent to 9.5 million pounds. The pollock harvest was decreased by 4.2 percent to 2.6 billion pounds. Better news for P-cod: Bering Sea fishermen got a 14.5 percent increase to more than 500 million pounds.


Laine Welch is a Kodiak-based fisheries journalist. Her Fish Radio programs can be heard on stations around the state. This material is protected by copyright. For information on reprinting, contact msfish@alaska.com.

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