NEW : `` More investigation needs to be done , '' says a marine biologist . Official : Marine biologists are still trying to determine the cause of those deaths . The dolphins were found over a 220-kilometer ( 137-mile ) area of coastal the United States early March . The dolphins were not caused by starvation or poisoning with pesticides , officials say . more than 800 of dolphins have also washed up in Brazil and the United States this year .
NEW : `` More investigation needs to be done , '' says a marine biologist . Official : The dolphins were found over a 220-kilometer ( 137-mile ) area of coastal the United States early March . The dolphins were not caused by starvation or poisoning with pesticides , officials say . more than 800 of dolphins have also washed up in Brazil and the United States this year .