Swimmers are being told not to be surprised if they see a highly venomous sea snake next to them in New Zealand oceans during summer.
The National Institute of Water and Atmospheric Research says yellow-bellied sea snakes, Pelamis platurus, are highly venomous, usually found in warm waters, and regularly wash up on North Island beaches, though they are not endemic to New Zealand.
"They live near the surface, hang around with logs and drifting seaweed, and feed on the fish that aggregate in those areas," said NIWA principal scientist Dr Malcolm Francis.
He said swimmers should not be surprised if they see such creatures swimming next to them during summer.
All sea snakes are poisonous, but generally require a lot of provocation before they will bite, Francis said.
Their mouths are small and fangs are set well back, making it hard for them to bite a human, he said.
This sea snake is related to the cobra, and has a pair of fangs that inject venom into its victim.
After biting its fish prey, the snake will eat it head first.
The yellow-bellied sea snake lives in the open sea and travels with surface ocean currents. It has a paddle-like tail that enables it to swim well.
Most of the recorded sightings of snakes in the New Zealand region, over the summer months, are from the northeast of the North Island, Francis said.
They have occasionally been spotted as far south as Cook Strait, he said.