Some 300 endangered sea turtles were found dead floating in the waters off Mexico's southern coast on August 28 after they were caught in fishing nets.
The deaths come days after more than a hundred of the same species perished due to unknown causes.
The dead olive ridley sea turtles were discovered by fishermen in the southern state of Oaxaca on Mexico's Pacific coast in a sector called the Barra de Colotepec, Oaxaca's civil protection coordinator Heliodoro Diaz told Reuters.
Images captured by Reuters showed dozens of dead turtles, many of them in a state of decomposition, lined up through what looked like a mesh or in groups.
The olive ridleys, chelonians in danger of extinction, measure about 75 centimeters (29 inches) and weigh around 45 kilos (99 pounds).
They arrive en masse on Mexico's Pacific coast every year to spawn between June and September, with some arriving as early as May.
The Latin American country, where six of the seven species of marine turtles that exist in the world nest, has a permanent protection program for the reptiles which includes a complete ban on killing turtles, use of turtle excluder devices in trawl nets, and protection of spawning areas, among other measures including prison sentences for those who kill them.
Mexico's office of the federal attorney for environmental protection (PROFEPA) said it was investigating the case.
In another case, authorities said they are investigating the deaths of 113 endangered marine turtles - 102 olive ridleys, six hawksbills and five of the species known as prieta, found in a sanctuary in Chiapas state which borders Oaxaca.
Video source: VCG