Los Angeles - Four dead dolphins have washed ashore with fatal bullet wounds and fifth with lacerations on its pectoral fin, said authorities who have offered a reward for information on the slayings.

The long-beaked common dolphins were all discovered between Carlsbad State Beach and Oceanside Harbor between May 29 and June 5. Photos showed their normally sleek gray skin mottled and stained with blood from the bullet wounds.

"It's a horrendous thing that happened," said Mark Oswell, spokesman for the National Oceanic & Atmospheric Administration. "That someone would go out there and shoot four dolphins."

Necropsies revealed that the dolphins, which were healthy with bellies full of fish, may have been shot at the same time with the same gun. Four had between one and three bullets of the same caliber in the same part of their heads.

Federal officials say that nationwide, they normally get one report of a dolphin shooting a year. The last time San Diego reported such a death was five years ago. Before that there hadn't been one in the area since the 1960s.

"It usually turns out to be a fisherman," said Oswell, adding there have been cases when anglers take out their frustrations on dolphins and other mammals that eat their catch.

The agency is offering up to $2,500 for information on the deaths. If caught, the perpetrator could face civil penalties of up to $12,000 or a criminal fine of up to $20,000, as well as jail time.

Harassing or killing dolphins is a violation of the Marine Mammal Protection Act of 1972, a federal law that protects seals, sea lions, dolphins, whales and other marine mammals.