Commercial fishermen can now trawl Louisiana’s waters for white shrimp as the season opened on Monday, but questions linger about the effects BP Plc’s Gulf of Mexico oil spill will have on the harvest.

Some state waters have been open for brown shrimping since the well ruptured on April 20, but the overall catch has been down from previous years partly because a number of boats are signed up with BP’s oil spill clean-up program.

The plump, sweet white shrimp are typically larger than brown shrimp and more desired by chefs. The U.S. government has said that seafood pulled from the areas of the Gulf of Mexico that is open to fishing is safe to eat despite all the oil that gushed into the ocean.

More than a fifth of federal waters in the Gulf remain closed due to fear of oil contaminating the seafood.