Authorities say a dog responsible for mauling a young fur seal to death on Pukehina Beach "refused to let go" of the terrified animal when beach goers tried to intervene.
The dog attacked the seal around the neck and head on Sunday. It later died as a result of its injuries "although not immediately". The seal was about 10 months old and about 60cm long.
DoC ranger Kate Miller said the unleashed dog "refused to let go".
"Witnesses had to intervene and pry the dog off the seal."
"A member of the public who witnessed the attack called the police and brought the seal in for DoC to collect," Ms Miller said.
She said they were investigating its options regarding prosecuting the owner of the dog over the attack.
Western Bay of Plenty District Council compliance and regulatory manager Alison Curtis said they were confirming the details of the incident and would then talk to the dog owner.
"Until then we can't specify dog type or details about what will happen next."
Pukehina beach is a "dogs under control" area, "meaning dogs may be on the beach off leash but must be under the owner's control," Ms Curtis said.
She said there had been no reports of attacks on seals in the past 20 years in the Western Bay.
Ms Miller said dog owners whose dog attacks a seal could face prosecution.
"It's an offence under the Marine Mammals Protection Act to disturb, harass, harm, injure or kill a seal," she said.
To ensure the safety of your dog and the seal, always put your dog on a lead when you were near a seal and keep an eye open for seals when walking on the beach, Ms Miller said.
The maximum penalty was two years' imprisonment or a fine to a maximum of $250,000.
Western Bay Wildlife Trust volunteer Rosalie Crawford was called to help a little blue penguin found in Papamoa after a dog attack.
The penguin, which they named Kirk, had been blinded after it was bitten through the skull by a dog, with a tooth reaching its right eye.
This had impacted on the bird's hunting abilities, said Ms Crawford, and caused the penguin to starve.
"The vet said the best thing for it was to put it down, we could feed it up but we couldn't release it into the wild again because it couldn't hunt," Ms Crawford said.
She said in the past year 24 penguins had been killed in dog attacks that the Western Bay Wildlife Trust knew about.
"It's a lot when you see them side by side, in a freezer waiting for burial," Ms Crawford said.
Western Bay Wildlife Trust team leader Julia Graham said she was called out to penguin incidents at Pukehina Beach "all the time".
She advised the public to give beached penguins space.
"If they're coming up into land they really need to get out of the water, they're not coming to say 'hi'. It's very, very frightening for them to have people surrounding them.
"Do not try to touch them at all."
Papamoa Beach Domain, Papamoa Beach Rd, Tauranga
When: Sunday September 18 2016, 11am-2pm
Where: Mt Maunganui Beach, Marine Parade, Mt Maunganui
When: Saturday September 17 2016 1.30pm - 4pm