It has called on the public to be “extra vigilant” around the coasts as there has been “an escalation” in “appalling incidents” in recent years, including the decapitation of two adult seals in Dingle this summer.
The two bloodied heads were mounted on plywood and nailed to the entrance of the Dingle Wildlife and Seal Sanctuary.
In Co Waterford alone, 11 seals have been clubbed or shot over the past year, according to the ISS.
In January, three grey seals and a dolphin were found dead on Tramore beach, Co Waterford, with “horrific” gun wounds. Nobody was charged for these attacks.
The ISS say seals are particularly at risk from attack by humans during their breeding season. The Irish Fish Producers Organisation (IFPO) has described the killings as the actions of some “disturbed individuals” while some in the fishing community have called for a legal cull of seals, claiming they are interfering with their catches.
The National Parks and Wildlife Service, meanwhile, is not funded to perform postmortems on any dead seals found in suspicious circumstances.
ISS founder Brendan Price said: “The birthing season is now beginning and will continue until Halloween when it will be at its peak. This period, inevitably, over the years, has afforded illegal seal-cullers their best opportunity to slaughter pups and nursing mothers on their coastal birthing grounds and the ISS appeals to all to tolerate no repeat of previous incidents.
“We are not laying any blame at the foot of the small fishermen but it is the owners of the bigger 50-60 metre trawlers that are posing the biggest threat. Some of the incidents that have taken place recently are just barbaric,” Mr Price said.
The IFPO said it is awaiting the results of a seal census being carried out by NPWS. “We don’t condone anything like illegal seal culling. If there is to be any management of seal numbers it has to be done based on sound scientific evidence,” said CEO Francis O’Donnell.
The Irish Seal Sanctuary is taking part in a working group along with the Marine Institute, Fisheries Research Council and IFPO to help find solutions for those affected by seals.
Grey seals are a protected species under the Wildlife Act 1976, but are often considered a pest within fishing communities.