It was a gruesome sight: 250 stingrays littering the beach at the edge of the Gulf of Mexico in the town of Ursulo Galvan in Veracruz state.

Now authorities are investigating whether there is a connection to the oil industry, though at least one witness told authorities she saw fishermen dump the carcasses from their nets onto Chachalacas beach. Although stingrays are a popular snack—the “wings” can be sautéed, and the meat tastes like scallops—these fish may have been discarded for lack of a good selling price.

However, one fisherman refuted that theory, telling BBC News that he had never seen such a thing happen during 30 years of plying the waters. Unwanted fish are always thrown back into the water alive, fisherman Jaime Vazquez told the network.