A mysterious shell disease that has been a chronic problem for the southern New England lobster industry for years seems to be creeping northward to the lobster-rich grounds off Maine.

Epizootic shell disease, which is not harmful to humans, is caused by bacteria that eat away at a lobster’s shell, leaving behind ugly lesions. Diseased lobsters can be processed, but they are not marketable in the more valuable live market. The disease stresses lobsters and sometimes kills them, but it doesn’t taint their meat.

The number of lobsters suffering from shell disease remains tiny in Maine. Only three of every 1,000 lobsters sampled last year had the disease, according to a report by the Associated Press. But scientists and lobstermen are worried because the prevalence of the disease grew fivefold from 2010-2012.

The disease first became noticeable in southern New England waters in the 1990s. About one in every three or four lobsters caught in waters off southern Massachusetts and Rhode Island in recent years has been diseased.

Lobster is one of the most important fisheries in Maine and throughout New England, valued at more than $400 million to fishermen and hundreds of millions more to coastal communities.

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