The Colombian tuna boat "El Dorado" was caught fishing in the reserve last Friday and forced into port, where officials found 50 dolphins had died or were dying in the ship's nets, Galapagos National Park said in a statement.

"We don't have an exact figure of how many died. Of these 50 dolphins more than half died. The majority died, very few were saved," park director Eliecer Cruz told Reuters by telephone.

El Dorado's crew had apparently cast its nets over dolphins swimming near a school of yellow-finned tuna without taking precautions to protect them, violating international norms designed to conserve marine mammals, the statement said.

Cruz said the boat, which worked with Ecuadorean tuna company INEPACA, was detained by marine authorities at a Galapagos port, some 625 miles (1000 km) west of Ecuador's coast.

Ecuador is locked in a battle over fishing rights in Galapagos with the tuna industry seeking access to its bountiful waters amid an outcry from environmental groups and animal lovers.