Crabs may be solution for tunicate threat

Mussel growers are turning to the native rock crab for help in battling an infestation of Ciona intestinalis, a tunicate which is making it difficult to harvest mussels in eastern P.E.I. and slowing their growth.

The tunicates don't hurt the safety or quality of mussels, but they compete for food and completely cover the socks the mussels are grown on, making harvesting an expensive, labour-intensive process.

"The major challenge here is that we're dealing with probably one of the worst of the four species that we've been involved with over the past five years," Department of Fisheries and Oceans scientist Thomas Landry told CBC News.

The tunicate are not a native species. They are invaders from Asia, travelling to P.E.I. on the hulls of boats.

The idea to battle the tunicate with crabs came from local fishermen.

In late August, almost 20 tonnes of rock crab, caught close by, were dumped onto a mussel lease in the Montague River. The mussel lines were weighed down to touch the bottom and create a ladder for the crabs to gain easy access.

"We do have some evidence that they actually eat them," said Landry.

Keeping costs down is an important issue for mussel farmers in eastern P.E.I. because their competitors won't let them increase prices.

Mussel farmers are hopeful that the rock crabs will make a significant contribution to keeping the mussel lines clean. As a side benefit, the crab can be caught again and sold for food.