Marine officers responded to vague reports of a "large dead whale" on a beach near Bridport on Wednesday.
Officers from the Department of Primary Industries, Parks, Water and Environment's Marine Conservation Program found a deceased sei whale dead on arrival.
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"Sei whales migrate past Tasmania's East Coast each year but it is rare to see them deceased on the beach," a department spokesperson said.
"Wildlife biologists will conduct a necropsy to try to determine a cause of death but it appears the whale may have had a long-term underlying issue.
"It is not yet been determined if it is male or female.
"Necropsy on a pygmy whale found dead at a separate beach at Bridport last week did not reveal any obvious cause of death."
Sightings or strandings can be reported to the Whale Hotline (0427 WHALES).