UMaine researchers: mussels can combat sea lice outbreaks

Sea lice on fish.
Courtesy of the University of Maine
Sea lice on fish.
Posted June 29, 2011, at 6:08 p.m.
Last modified June 29, 2011, at 7:53 p.m.

ELLSWORTH, Maine — With the help of a local mollusk, researchers at University of Maine think they may have found a way to combat the spread of a destructive marine parasite.

Sea lice, as the copepods are commonly called, have been the scourge of salmon farms in Maine, particularly in Passamaquoddy and Cobscook bays, where they fasten themselves to the caged fish, adversely affecting their health and appearance. In attempts to kill off the parasite, aquaculture operators have developed ways to treat affected fish with pesticides that critics say are harmful to the marine environment in general and to lobsters in particular.

Lobsters, like sea lice, are crustaceans and have the same vulnerabilities to the pesticides that the sea lice do, according to lobster industry officials. If the pesticides are not applied properly, environmentalists and lobster industry officials have said, the chemicals could kill lobsters that are near the pens where salmon are being treated.

The use of pesticides on the Canadian side of Passamaquoddy Bay is being investigated by federal authorities in that country. Traces of cypermethrin, a pesticide approved in Maine for combating sea lice but banned in Canada, was found in early 2010 on dead lobsters collected off of Deer Island, within a few miles of the American border.

According to an email sent Tuesday to the Bangor Daily News by a spokesperson with Environment Canada, the Canadian agency is investigating the mysterious lobster deaths.

In Maine, the lobster and farmed salmon industries represent the state’s two largest commercial fisheries. According to updated statistics from Maine Department of Marine Resources, Maine lobstermen earned $313 million from the 94.7 million pounds of lobster they caught in 2010. Aquaculture operators earned $76.7 million in gross revenue last year from the 24.5 million pounds of farmed salmon they cultivated in Maine, the statistics indicate.

Ian Bricknell, professor at UMaine’s School of Marine Sciences, said Wednesday that researchers have collected blue mussels from the Maine shore and found larval sea lice in their stomachs and intestines. This discovery, he said, could prove beneficial to not only the state’s farmed salmon and lobster industries, but to other commercial fisheries as well.

“It’s a very exciting piece of work,” Bricknell said of the research. “It’s a huge benefit.”

Bricknell said researchers plan to test the effectiveness of using mussels to combat sea lice by placing a fully loaded mussel aquaculture raft at an undetermined salmon aquaculture site in Washington County sometime this summer. The mussels will be attached to ropes that hang down 15 feet into the water, which he said is the maximum depth at which sea lice are commonly found.

Bricknell said that, if the mussels prove effective, a ring of mussel rafts could be placed around a group of salmon pens, effectively shielding the fish from sea lice. To round out the site’s productivity, he said, seaweed could be cultivated in a larger area surrounding the mussel rafts. Seaweed growth is enhanced by nitrogen and phosphates that are found in salmon effluent, he said. Seaweed has applications in the pharmaceutical and biofuel industries, he said, or like the mussels and salmon, could be cultivated for human consumption.

“You would have a whole ecosystem where you would have four or five crops,” Bricknell said.

The UMaine professor said the presence of mussels likely would not completely eliminate the use of pesticides in salmon aquaculture, but it could reduce it significantly.

“We won’t know until we actually get the trials done,” he said.

Sebastien Belle, executive director of Maine Aquaculture Association, said Wednesday that cultivating mussels at salmon farms is not new, but that up until now it’s been done for other purposes. It was a matter of convenience for aquaculture operators who wanted to cultivate more than one species, he said, and the mussels helped filter suspended solids generated in the water by the salmon.

He said it is “very exciting” that researchers have discovered that mussels eat larval sea lice.

“That was a novel idea,” Belle said. “It’s early days yet to see how effective it is.”

Salmon growers already use other techniques such as rotating pens among distant locations and letting some sites lie fallow as a way to combat sea lice outbreaks.

“This is now a second nonchemical method of [sea lice] control,” he said.

Follow BDN Reporter Bill Trotter on Twitter at @billtrotter.

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