Mystery surrounds death of 137 sea lions who washed up on beach
Mexico's office for environmental protection has said the animals do not have injuries from getting caught up in fishing nets.

Mexican authorities are investigating after 137 dead sea lions washed up on a beach with no sign of how they died.

The country's office for environmental protection has said the animals do not have injuries from getting caught up in fishing nets or lines.

There are also no marks on their bodies from possible collisions with boats.

Both scenarios are common causes of sea lion deaths or injuries.

The environmental protection office said tissue samples had been collected from some of the bodies for analysis to determine how the animals died.

The bodies were found along an 80 mile (130km) stretch of coast in the area of Comondu, in Baja California Sur state.

California sea lions are a protected species in Mexico but are not considered to be in danger of extinction there.