Tuna bring in big money for some fishermen in the Maritimes. (CBC)

The oil spill in the Gulf of Mexico could have a serious long-term impact on tuna stocks off Atlantic Canada.

The Gulf is the spawning ground for bluefin tuna that migrate to the Atlantic region.

"Many fish are going down to the Gulf to spawn," said Jackie Savitz, a marine biologist with Oceana, an international conservation group based in Washington.

"The larvae of the fish is actually the most sensitive life stage to the toxic effects of oil. And one fish that's spawning right now down there is the bluefin tuna."

There is already concern for the health of the Atlantic bluefin tuna population. It has fallen 90 per cent since the 1970s, and the World Wildlife Fund says the species faces a serious risk of extinction. Stocks in the western Atlantic are in better shape than in the east, and the oil spill strikes at an economically important fishery in Atlantic Canada.

"It's definitely going to have some effect on the spawning mass and the juveniles," said Walter Bruce, chair of the P.E.I. Tuna Working Group.

"The bigger fish, the giants as we call them, most of them I would think, are out of that area by now and on their way this way. So it may not affect the next few years … but 10 years down the road we could see a big decline in the catch."

Oyster fishers could benefit

The spill has also shut down one of the largest oyster fisheries in the U.S., which could bring a sales boost for other oyster producers.

While Rory McLellan of the P.E.I. Shellfish Association takes no joy in it, he expects the closure of the fishery in the Gulf of Mexico will mean higher prices for oysters coming out of the Gulf of St. Lawrence.

"While the animal is not exactly the same as ours, some of the markets are the same," said McLellan. "If, God forbid, they're not able to save that shoreline, it should increase demand for oysters coming in from Canada."

The oil spill began April 20 after a drill rig exploded off the coast of Louisiana. Officials estimate it is spilling nearly 5,000 barrels a day, and it could be months before the flow is stopped.