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Lobster Shell Disease Could Pose Threat To Maine Seafood Market: Are Rising Water Temperatures And Pollution To Blame?

Clone of lobster shell
Lobster shell disease has seen an fivefold increase in the last two years, causing experts to wonder what ecological changes have caused the spike. Sea Grant Rhode Island

Lobster shell disease, a discoloration of the lobster’s shell that is both a cosmetic and life-threatening problem, has been moving its way north to Maine, the Associated Press reported.

A disease that ran rampant in New England for years, lobster shell disease causes the animal’s classic red shell to turn a murky black, making the crustacean unmarketable depending on the severity, and despite no change in taste to its meat. Now, the disease has seemed to migrate north, toward Maine, as its prevalence has grown fivefold in the last two years.

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Lobster shell disease first plagued New England waters in the 1990s. In recent years, one out of every three or four lobsters found off southern Massachusetts and Rhode Island bore the disease, which, while not harmful to humans, can spell trouble for the lobsters themselves. Marked by a black spot initially, the disease is caused by bacteria that eat away at the animal’s shell and prevent it from molting, perhaps even killing the lobster.

For as prevalent as the disease is in southern New England waters, the rate of incidence is still extremely low in the colder, more northern regions — from 2008 to 2010, observers found about one diseased lobster for every 2,000 sampled in Maine. In 2011, that rate rose to four diseased lobsters in 2,000, and in 2012, it rose to six, the Associated Press reports.

People should not be alarmed by these increases, said Carl Wilson, state lobster biologist for the Department of Marine Resources. People could see the numbers and have the tendency to say, "Oh, my god, that's a huge increase," he said.

"But it's not, considering all the sampling we have and all the caveats of our sampling design," Wilson said. "But it's something we are watching."

The ecological, economical, and biological all play a role in sustaining the Maine lobster population. While the cause of shell disease is unknown, many experts speculate that the rising water temperatures, pollution, and decreasing levels of oxygen in the water have contributed to rises in recent years. The water off the coast of Maine as it faces Nova Scotia has been characteristically colder than the waters further south, and it’s for this reason that experts believe the problem may be overstated.

"It's certainly something to keep an eye on. But in terms of our perspective of Gulf of Maine shell disease, we don't see it as something to get particularly concerned about," said Tracy Pugh, a fisheries biologist with the Massachusetts Division of Marine Fisheries. "The rates are pretty low. We don't see a pattern."

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Lobster accounts for 65 percent, or $400 million, of Maine’s fisheries. An infected lobster population could threaten the state’s infrastructure as it pertains to the seafood market. Because lobsters need to molt — that is, shed their exoskeleton — in order to grow, bacteria that infest their shell prevent the molting process from taking place. Female lobsters face the greatest risk because molting doesn’t occur while carrying eggs.

“Some preliminary studies suggest the lobsters may be contracting the disease from alkylphenols, chemicals that are byproducts from industrial sources,” the Rhode Island Sea Grant Fact Sheet reports. “These compounds are found in everything from detergents to surfactants (a surface-active substance), paints, and plastics, and have been found in higher concentrations in lobsters with shell disease than in unaffected animals.”

And while the rates are low, the rise is noticeable and cause for concern, among fishermen and experts alike.

"If we go all day long and I see a few that have shell disease, I think to myself, 'That's a lot,'" lifetime South Bristol lobsterman Arnold Gamage Jr. told the AP. "And I suppose it is a lot compared to none. But it's still a very small number; it's way less than 1 percent."

Wilson agreed, adding that Maine’s dependence on the lobsters’ health makes watching the problem more of an issue, even if the rates are low. Increases at all could prove disastrous, he said.

"I think when you have such a high dependence on single fishery, how could you not have a concern?" Wilson said. "There can be threats to the lobster population that are completely out of the influence of the fishermen, so any change is going to be a concern."

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