Shepherd Aaron Le Couteur, who visits the site daily, discovered the badly bitten lambs from the Manx Loagthan flock when he visited the National Trust land on Saturday morning.
It is believed the attack took place on Friday evening or early on Saturday morning.
Mr Le Couteur immediately called vet John Mather and following X-rays the decision was made to put them to sleep.
Trust lands manager Jon Horn said it was a tragic blow to the project.
Anyone with information should contact the police on 612612, Crimestoppers anonymously on 0800 555111, or Mr Le Couteur on 07797 740202.
See Tuesday’s JEP for full story.