Colton Hal Clements, 18, was one of three Kings County teens charged after 50 seals were found dead or dying on a shore near Beach Point in January.
A veterinary pathologist from the Atlantic Veterinary College examined 10 of the carcasses and determined the animals had been bludgeoned.
After an investigation by RCMP and the federal Department of Fisheries of Oceans, the three teenagers were arrested and charged with animal cruelty.
Clements also pleaded guilty to one count of disturbing marine mammals, which is a violation of the federal Fisheries Act.
Clements was the only one of the three charged as an adult. The other two accused were 15 and 17 at the time of the incident, and their names cannot be published. They have yet to go to trial.
The court heard Clements is currently attending school and had no prior criminal record.
Clements will be sentenced June 6 in Georgetown provincial court.
At that time, an agreed statement of facts will be read.