Four sea lions, 11 sea turtles and 21 dolphins have mysteriously turned up dead on an island in northwestern Mexico, sparking an investigation, authorities said Thursday.

The animals were found on Altamura Island, Sinaloa state, in the Gulf of California, according to the federal prosecutor's office for environmental protection (Profepa).

Profepa said in a statement that inspectors, park rangers and other experts were dispatched along 42 kilometers (26 miles) of coast to investigate the "unusual event."

They will collect evidence to figure out how the animals died, the statement said.