Marine biologist explains why tropical species like venomous sea snakes end up in Aotearoa

A marine biologist says a "conveyer belt of surface ocean currents" is what pulls tropical species to Aotearoa's waters, after a banded sea krait was spotted in Auckland's harbour on Tuesday.

The sea krait, a highly venomous sea snake, was seen swimming in Auckland's harbour early on Tuesday morning. 

Marine biologist Riley Elliot told AM Aotearoa is not a common destination for the sea snake, but its arrival was driven here by a recent weather event. 

"That big rainfall we had a couple of days ago, and what we're seeing more with La Niña when we get those big blocking highs off the east of New Zealand, and those lows that drive all that tropical water down to us - that's like a conveyer belt of surface ocean currents."

Elliot said when animals are small and need to breathe air they stay close to the ocean's surface instead of heading below the current. 

"They just get driven down here and it's no surprise that most summers we start to see the arrival of some of these tropical species."

He said the sea kraits' arrival is "a sign of us getting our tropical summer water".

But the warmer water for us isn't enough for these tropical species to survive. 

"I don't think anything is going to survive down here, it is much much cooler, our water temperature right now is about 19 degrees, these guys need to survive above 20 degrees," he said. 

"It's much cooler than their usual environment so they're struggling to stay alive."

He said, like most reptiles, when the sea krait is cold it may stop moving.

"The golden rule here is don't go touch one, it may appear dead but if it swings around and bites you… The best thing you can do is call 0800 DOC HOT so we can understand their distributions," Elliot told Newshub. 

"Any animal that is compromised will lash out if annoyed."

He said while the sea snake is highly venomous, "it's important not to panic". 

"Stay as far away from the snake as you can."

Watch the full interview above.