During the last several months, dolphins have washed ashore along the northern Gulf Coast with bullet wounds, missing jaws and hacked-off fins and federal officials said they are looking into the mysterious deaths.
The most recent case was of a dolphin found dead off the coast of Mississippi, its lower jaw missing, according to the Associated Press.
Officials from the National Oceanic and Atmospheric Administration told AP that they're asking beach-goers, fishermen and wildlife agents to be on the lookout for injured or dead dolphins and any unusual interaction between the mammals and people.
"It's very sad to think that anyone could do that to any animal," Erin Fougeres, a marine mammal scientist for NOAA's southeast office in St. Petersburg, Fla., told the AP. "There have been some obviously intentional cases."
The California-based Animal Legal Defense Fund said it is offering a $5,000 reward for information leading to the arrest and conviction of whoever harmed the dolphins.
Fougeres said dolphins began stranding themselves two months before the 2010 oil spill disaster off the coast of Louisiana and there were unusually high mortality rates, possibly because of a cold winter that year.
Since then, the spill and another cold winter in 2011 have contributed to several deaths within the Gulf's dolphin population, experts say. Investigators also have found discolored teeth and lung infections in some of the dead dolphins.
Experts have tallied more than 700 recorded dolphin deaths since February 2010.