NEW : ` ` More investigation needs to be done , '' said a marine biologist . Official : The whales were found over a large ( 137-mile ) area of coastal Peru this year . The deaths were not caused by fishing or treatment with pesticides , officials say . Dozens of whales have also washed up in the United States and Brazil 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 Peru this year . The dolphins were not caused by starvation or poisoning with pesticides , officials say . Dozens of dolphins have also washed up in the United States and Brazil this year .