(CNN) -- They're friendly, intelligent and playful. So who'd want to shoot a dolphin?
Conservation experts and federal agents say they're looking into the violent deaths of several bottlenose dolphins along the northern Gulf Coast this year, including one that was shot and another that was stabbed with a screwdriver.
"I can't explain why anyone would shoot a dolphin," Jeff Radonski, a Florida-based special agent for the National Oceanic and Atmospheric Administration, told CNN. Radonski said NOAA is investigating four of the six deaths reported since June.
Samia Ahmad, a spokeswoman for the Institute for Marine Mammal Studies in Gulfport, Mississippi, said at least six dolphins had died as a result of foul play since January. In one case, a dolphin had its jaw cut off, she said.
In September, a dolphin that washed up on Elmer's Island, Louisiana, had been shot. The bullet that killed it was found in its lung, NOAA reported. In June, a bottlenose was found in Perdido Bay, on the Florida-Alabama state line, with a screwdriver stuck in its head, the agency said.
Dolphins are covered by the Marine Mammal Protection Act, a 1972 law that makes killing them punishable by fines of up to $20,000 and a year in prison. In at least two previous cases, fishing charter captains have been found guilty of shooting at dolphins that approached their boats or the fish their passengers had hooked, NOAA says.
NOAA spokeswoman Allison Garrett told CNN that the most recent prosecution involved a Panama City, Florida, man who was convicted of throwing pipe bombs at dolphins. He was sentenced to two years in prison in 2009 for violating the federal conservation law and for possessing an explosive device as a convicted felon.