Penguin Trust ranger Reuben Lane said the dogs responsible should be shot.
He said some Cape Foulwind/Omau residents had provided helpful information on wandering dogs, but it would be extremely hard to prove which had killed the penguins.
Neither DOC, council nor the penguin trust had the financial resources for a forensic investigation.
Mr Lane said he found the latest dead penguins all over the beach and in the bush yesterday afternoon at Siberia Bay. The carcasses were surrounded by dog pawprints.
Both he and the vet who had examined the penguins were certain they had been killed by dogs.
Some of the penguins were just metres from their burrows and had almost made it to safety. They waited until dark to come ashore en masse to avoid their natural predators. They wouldn't have stood a chance against dogs and it was likely the dogs had got every last one.
Fifteen adult penguins represented a significant breeding colony.
Some of the largest colonies on the Coast had only 20 burrows.
The West Coast was a harsh place for penguins to survive, without dog attacks.
So many adult deaths was "a bloody tragedy".
Only about 50 per cent of chicks reached adulthood, so one adult penguin was worth about six chicks. "They're feisty little birds, but no match for a dog. It's naive to think you could have a dog and let it do what it likes and this won't happen."
The penguin breeding season was about to begin.
He hoped the dog owners were merely grossly negligent, rather than complicit in the penguin deaths.
Farmers had no compunction about shooting dogs on their property and neither should the public if they saw untagged dogs wandering free, said Mr Lane. At the very least they should call dog control.
He suggested bird aversion courses to stop dogs attacking birds.
Despite the setback the trust would carry on with its work.
DOC's Buller area manager Bob Dickson said penguin massacres, all by dogs, had happened in the Cape Foulwind area over a number of years.
More coastal housing developments brought more dogs, he said. They should not be allowed to run free, especially at night when birds were returning to their nests.
The area was highly valued by both locals and visitors and DOC and the penguin trust had put a lot of time and resources into the area, including predator control.
The work was pointless if it was going to be under threat from renegade dog owners.
"If the penguin trust wants to proceed with its work in the area, it needs to have trust that all its work won't be undone."
Mr Dickson would not say if DOC would be calling for a ban on dogs in any new coastal subdivisions. The problem was irresponsible owners, not responsible ones, he said.
In general, he believed awareness around protecting weka and penguins was growing.
He wasn't interested in DOC providing bird aversion courses.
Buller District Council compliance team leader Atila de Oliveira said council would give DOC 100 per cent support to find the culprits.
