A 2.3 metre blue shark that washed up on a beach north of Auckland today was covered with bite marks - the kind that come from mating, not fighting.

A paddle boarder alerted the Department of Conservation to the blue shark after it was seen floating in shallow water at Stanmore Bay this morning. It then washed up on the beach at low tide this afternoon.

Massey University scientist Dr Adam Smith, who collected the shark at about 5pm, said it had bite wounds - but they are unlikely to have been fatal.

"The wounds didn't look particularly damaging. Shark are quite hardy fish. They can heal wounds. It didn't look like any of those would be the cause of death."


Smith said the teeth marks were more likely from mating and the mature female shark - estimated to be about 10 years old - may have been pregnant.

The shark was reported to have been seen floating in the water yesterday, but Smith did not think it had been dead longer than a day.

"Blue sharks are definitely fairly common in New Zealand waters. You don't tend to get them washing up that often. Fisherman say they see them fairly regularly, particularly in summer."

He said the blue shark was not considered dangerous and people should not be afraid of entering the water.

"Shark attacks are very rare in New Zealand and this is not a species that is generally aggressive."

People on the beach also reported seeing orcas and bottle nose dolphins along Whangaparoa Peninsula this afternoon.

Smith said the shark would now join Auckland Museum's research collection.

The museum only had two blue sharks in its marine collection so the latest discovery was welcomed.

Head of natural sciences Dr Tom Trnski said tissue samples would be taken for genetic analysis. Samples of any sperm would indicate how many different individuals the shark had mated with.

"Even though blue sharks are quite common sharks, there's still quite a bit about their biology that we don't know so any other information we can get on their reproductive cycle, their diet or anything like that is adding information to our knowledge of the species and its biology.

"Blue shark are just one of the most beautiful looking sharks. So sleek and slender."

The shark will be stored on ice and eventually preserved so it can be stored at the museum.