Ursulo Galvan, Mexico - Mexican authorities investigating the deaths of at least 250 rays found on a beach say they are studying whether work being done by the country's national oil company in the Gulf of Mexico might have been involved.

Veracruz state fishing director Tomas Rubio says his office will try to determine if the rays were poisoned or otherwise affected by Petroleos Mexicanos. Rubio said Wednesday that there is no evidence so far Pemex caused the deaths.

Officials also are looking into reports from witnesses who said fishermen dumped the rays because they weren't able to get a good price for them. Chopped stingray wings are commonly served as snacks in Veracruz restaurants.

Residents and visitors first spotted the dead rays last Tuesday on the Chachalacas beach in the town of Ursulo Galvan.