At least 300 turtles have been found dead Thursday on the coast of Mexico, turning the country’s Southern coast into a marine cemetery.

Mexico’s environment ministry revealed that all dead turtles were female and they were entangled in illegal or abandoned fishing nets.

“The number of dead turtles is quite high and, according to the first analysis, it has been established that they died from asphyxia,” Helena Iturribarria, head of the Ministry of the Environment, Energy and Sustainable Development, told the Latin American news outlet Infobae.

“Since they were trapped in a deep-sea net used by illegal and clandestine fishermen. They were caught in the nets and, unable to escape, they suffocated. Their corpses ended up being washed by the current to the beach, " Iturribarria added.

The turtles were from the olive ridley species, which have been listed as vulnerable by the International Union for the Conservation of Nature (IUCN) since their decreasing population can only nest in a small number of places, BBC News noted.

Mexico officials said environmental authorities and the navy will work together to further investigate the nature of the mass turtle incident and determine an official cause of death, according to BBC News.