Published Wednesday, 26 September 2012
It is understood the carcass was found by a man out walking. (© UTV)
The animal's body was discovered along the North Coast on Wednesday afternoon.
Eyewitness reports suggested it may have suffered a gunshot wound to the head.
The NI Environment Agency said the carcass has been removed and a post mortem investigation is underway to determine how the seal died.
A statement to UTV said: "Northern Ireland Environment Agency (NIEA) has been informed of the location of the carcass of a seal.
"The carcass has been removed and there is currently a post mortem investigation underway, the results of which will be known within a few days and will confirm whether or not this seal had been shot."
Police said they have been made aware of the matter.
A statement said: "Police have been made aware of a report of a dead seal carcass found at Castlerock beach this afternoon (Wednesday 26th September)."
The NIEA urged anyone who witnesses incidents like this to report them.
It continued: "NIEA would encourage the public always to report suspected incidents of wildlife crime immediately to their local PSNI station."
Green Party MLA Steven Agnew has appealed for the public to remain vigilant on wildlife crime.
"I cannot understand the mentality of anyone who would do this or in fact inflict pain and suffering on any animal - domestic or wild," he said.
"It is incumbent on everyone in Northern Ireland to look after the welfare of wildlife as the police cannot be everywhere so I appeal to the public to be vigilant to wildlife crime and report it to the police.
"Moreover, our local wildlife is constantly under threat from all manner of hazards and their deliberate killing robs all of us of our precious natural biodiversity."