Tasmanian environment department marine biologist Sam Thalmann said the seal, with a distinctive numerical marking on its flank, was seen foraging in coastal waters off Victoria recently.

The male long-nosed fur seal, also long in the tooth, has Australian scientists questioning their understanding of the life spans of the animal which was previously thought to live to just 19-years-old.

"This sighting of the fur seal 25 years after it was marked as a pup provides exciting new knowledge into the maximum life span for wild fur seals in Australia," Mr Thalmann said.

"We were excited to respond to this call and gain important updated information from research activities conducted more than 20 years ago."

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He said that understanding the life history dynamics such as age structure, survival, longevity and dispersal of wild, far-ranging marine species such as fur seals is difficult to establish, but it is fundamental in conservation management and planning.

"We see a lot of older male fur seals that are past their prime and haul out along the Tasmanian coast as they reach their end of life, but this seal does not fit in this category," Mr Thalmann said.

"This seal appears to be in good physical condition and may continue to prosper for years to come."

Mr Thalmann said the seals were hunted to near extinction in the 1800s, and formed the first breeding colony on Maatsuyker Island, off Tasmania's south-west in 1987.

When this particular seal was born, less than 100 pups were born annually.

Members of the public are encouraged to report sightings of whales and injured or entangled marine mammals to the whale hotline (0427 WHALES).