Stuff reader Kimberley Collins took this photograph - from a safe distance - of a leopard seal that visited Caroline Bay on Saturday. Scientist Dr Krista Hupman said she was keen to put together "the pieces of the puzzle" when it came to the leopard seals, and she urged people to get in touch if they spied the visitor to Caroline Bay.

A leopard seal stopped over in Caroline Bay over the weekend and anyone who sees one has been urged to report their sighting.

The seal was last seen snoozing - and snorting - on the beach on Saturday. It had moved on by Sunday.

According to the Department of Conservation, it was probably resting after hunting.

Leopard seals breed in the Antarctic, but are occasional visitors to New Zealand shores.

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​NIWA cetacean biologist Dr Krista Hupman, who is conducting research into leopard seals, said how long the seal would stay on the coast, and where it would go next, was "anyone's guess".

"Some stop for years at a time."

It was unknown what would have drawn the seal to Caroline Bay. Scientists did not even know what temperature of water or type of beach they preferred.

"We know nothing about them in New Zealand," she said.

The last she had heard of the Caroline Bay seal was a report on Saturday.

Stuff news director Grant Shimmin saw the seal on Saturday morning, after hearing a "snorting noise" while running along the beach.

"I've seen one before, not at Caroline Bay, but up at Temuka a few years ago and this one seemed relatively small by comparison. My sense was that it was a juvenile," Shimmin said.

Hupman said she was keen to put together "the pieces of the puzzle" and urged people to get in touch if they spied another leopard seal.

She was compiling public sightings via 0800 LEOPARD (0800 566 7273) and the Leopard Seal Sightings Facebook page.

The seals have been described as a "vagrant species" but they did not fit the pattern of other species which travelled up to New Zealand from Antarctica, Hupman said.

Sightings were far more common. In the last week alone, she had received reports of six different seals in six different locations.

It was hard to say whether their numbers were increasing, or whether it was due to people being "out and about" with their phones and being more likely to photograph and report the animals.

Leopard seals are the second largest species of seal after the elephant seal, and are second only to killer whales as Antarctic apex predators.

They can live for between 12-15 years.

They are known to feed on penguins, sea birds, fish and other smaller species of seals, but are aggressive and potentially dangerous to humans.

Hupman said she believed anyone adhering to DOC's 20m distance rule would be safe: "I guess to me, leopard seals will not be aggressive if you stay away," she said.

It was a "personal choice" whether someone swam in water at a beach where a leopard seal had been spotted.

"Personally I believe that you should give the animals their space," she said.

Hupman was unable to discern fro photographs how large the leopard seal was, or whether it was male or female.

Those who harass seals can be prosecuted, and either ordered to pay a fine or sentenced to a term of imprisonment.