Are mosquito-control efforts killing lobsters?

The Providence (R.I.) Journal ran a story Tuesday about how a group of lobstermen are convinced that a mosquito larvacide is washing into the sea and killing local lobsters.

Methoprene is a chemical that mimics juvenile growth hormones in insects. It does not kill adult insects, but it keeps larvae from molting into adults, preventing them from reaching maturity. It is not believed to be toxic to humans.

The chemical is widely used throughout the world. In 2000, amid fears of West Nile virus, public works crews in Rhode Island began dropping it into tens of thousands of storm drains around Narragansett Bay.

Since then, lobstermen have seen their catch drop by more than half. The ProJo reports:

Local lobster catches topped off in 1999 at about 3,500 tons. Each of the following years has been progressively worse. In 2005, the last year with complete figures, the take was less than 1,500 tons.

In response, the lobstermen have greatly reduced the number of traps they set and accepted one new size restriction after another designed to leave lobsters in the water longer so they can successfully reproduce.

Still, the catch remains low. And many lobsters, particularly those caught close to shore, are coming up with a disfiguring, and still unexplained, shell disease.

Now the lobstermen are finding oddities never seen before in their traps: female lobsters that have molted their shells while they are still covered with eggs.

What they are not seeing is even more disturbing — young lobsters.

So far, the lobstermen, backed by the Rhode Island Lobstermen’s Association and Save the Bay, have persuaded 11 Rhode Island cities and towns to stop using methoprene. Only Providence has refused.

One state representative has introduced a bill banning methoprene's use throughout the state.

But scientists say there is no evidence that methoprene – which has been used for 35 years – is responsible for the decline in lobster populations.