It was rare for a Weddell seal to be seen on Dunedin beaches, as they were usually found around the Antarctic.
"It's pretty special that it's arrived and spending time on the beach here. We're not sure why."
Fyfe said the owner of the dog had contacted Doc to report the incident.
"It's certainly disappointing that these rare species that do visit are harassed and attacked in this sort of way by our four-legged friends," Fyfe said.
It was up to dog owners to check beaches before letting dogs off their leash, he said.
If they did see any wildlife, there was a bylaw that stated they had to keep dogs on their leash within 20m of it.