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Water | Environment

Farming Geoducks: A Mixed Bag For Tidal Critters

OLYMPIA — Geoducks. What funny, controversial creatures.

These giant clams occur naturally in the deeper coastal waters of the Northwest. They can live up to 150 years, all in the same place –- their long siphons snaking up through the muck to suck nutrients out of the water. And they’re fetching high prices in Asia right now where they’re a delicacy – and valued as an aphrodisiac (which is not surprising given their looks).

That’s made shellfish farmers in Washington increasingly interested in cultivating these clams. There have been about 350 acres of mudflats in Puget Sound dedicated to geoduck farming since 2007, when the last geoduck farm was permitted.

Why the moratorium on new geoduck farms? Well, if you’ve ever seen one of these farms at low tide, it can be rather scary looking. Row upon row of white tubes are stuck into the mud with about two baby geoducks planted inside each tube. Then those tubes are covered with nets that keep predators from stopping by for a free geoduck meal.

To harvest the geoducks once they’ve reached about 5-6 years of age, long hoses called “stingers” or “wands” are used to inject water into the mudflat, liquefying it so that the clams can be easily extracted.

Now, if you’re a beachfront homeowner and you’re watching this happening outside your window, you might be alarmed. Several years ago environmental activists and homeowners associations raised concerns about what geoduck farming might be doing to the surrounding environment.

The state Legislature responded in 2007. It authorized research through Washington Sea Grant to look at the ecological impacts of geoduck aquaculture.

Five years later, the results are starting to come in. The verdict so far: Geoduck tubes and nets change the species makeup, but there’s no immediate cause for concern.

“What we can say is there are a lot of species that settle on the tubes and the netting that we would not otherwise see generally in that type of habitat,” says the University of Washington’s Glenn VanBlaricom. He’s one of the research effort’s leaders.

VanBlaricom specializes in studying the thousands of different tiny animals –- less than an inch in size -– that make up the largest percentage of the species that inhabit tidal mudflats.

The numbers of these little guys dip when the tubes and nets come out and the geoducks are harvested (using the “stinger” to inject water into the mud).

But, VanBlaricom says, these creatures are adapted to the pounding of waves and pressure of tides. After a geoduck harvest he says there are minor temporary changes but a very quick recovery to a normal configuration of the ecosystem. “We certainly don’t see major changes such as local extinction or anything like that,” he says. “It’s just not that dramatic. We think the animals can cope with it pretty well despite the fact that it is a bit upsetting to watch it.”

Moving up the food chain from the little guys, scientists say there are winners and losers when geoduck tubes and nets go in.

“Animals tend to aggregate around structures,” explains Sean McDonald, a researcher in the school of Aquatic and Fisheries Science at the University of Washington. “There’s a lot of animals that prefer habitat complexity. Things like crabs like to crawl on and around the tubes and the nets.”

But not everyone wins. Species such as flatfish, sole and halibut – creatures that prefer to be on sandy bottoms where they can blend into their habitat – aren’t as numerous around geoduck farms as the mussels, barnacles, crabs and other fish that use the nets and tubes to hide and forage for food.

And then there’s eelgrass. This protected species of seagrass has been shown to provide habitat for juvenile salmon and other creatures. Micah Horwith is a postdoctoral fellow in the biology department at the University of Washington and has been studying how eelgrass and geoduck farming interact in Samish Bay.

Geoduck farming is never permitted in existing eelgrass beds. In 2002 Taylor Shellfish installed a geoduck farm on Fisk Bar in Samish Bay. There was no eelgrass present when they installed the tubes and nets but it started growing on the site soon afterwards.

Part of the grass survived the harvest of that geoduck crop but all the eelgrass was lost when the next crop of juvenile geoducks (in their tubes and nets) were put in at the site soon thereafter.

“The implantation of the tubes and the installation of nets allowed green algae to recruit to the nets and shaded out the grass beneath it so all the seagrass was lost within the geoduck farm because it was shaded out.” Horwith explains.

When the nets and tubes were removed once again, the eelgrass came back.

So, scientists agree that farming geoduck does change the makeup of the tidal ecosystem. But what is the the cumulative impact of increased geoduck aquaculture?

“There is an effect, but the million dollar question,” says Sean McDonald, “is ‘what is the long term ramification of those changes?’”

It’s a bit of a Catch-22, but that may be a question that’s impossible to answer until there are actually more geoduck farms to study. In the meantime though, McDonald and others say the key is to envision tidelands as a mosaic, not a monoculture of aquaculture.

“You don’t need just eelgrass beds or just mudflats or just oyster reefs,” he says. “You need that complex coverage of different types of habitats to make a system function at its best.”

Right now the Army Corps of Engineers is considering seven permits for new geoduck farms in Washington. These scientists hope the research they presented this week will play a role in how the burgeoning geoduck farming industry is planned and managed in the future.