The country’s environmental protection office said the animals were not injured by the nets or fishing lines.
There are also no marks on their bodies of possible collisions with boats.
Both scenarios are common causes of seal death or injury.
The Environmental Protection Bureau said tissue samples were taken from some of the bodies for analysis to determine how the animals died.
The bodies were found along a 130 km coastline in the Comondu region of Baja California Sur state.
California sea lions are a protected species in Mexico but are not considered endangered there.