SAN JOSE, Costa Rica (AP) — The Costa Rican government says illegal fishing could be the cause of 280 sea turtles showing up dead in the Golfo Dulce off the Pacific coast.

Environment ministry official Jackelyn Rivera says her agency has launched an investigation and ordered the Coast Guard to patrol the area more heavily in search of those responsible.

Some 280 sea turtles showed up dead on Monday. They were Kemp's ridley and black turtles, both endangered varieties.

Environmentalist Didier Chacon said Tuesday that the damage could have been done by long-line fishing, in which a rope with hooks is buoyed for miles to catch swordfish, but also snags other marine life in the process. Chacon said the method is illegal, especially in marine conservation areas such as the Golfo Dulce.