Large swarms of krill have been spotted floating off the Kaikōura coastline, with seabirds and fish feasting on the crustaceans.
While krill or squat lobster are often found in the area, South Pacific Helicopters and Wings Over Whales owner Daniel Stevenson says he has seen more of the crustaceans than usual in recent weeks, within five kilometres of the coastline.
"It's the most I've ever seen actually, it has been quite impressive - it can either be a light greeny colour or a deep red colour, like the squat lobster, big clouds of it through the ocean and you see birds and fish feeding on it."
Department of Conservation principal science advisor Graeme Taylor said Kaikōura was a well known hotspot for marine life, with krill a favoured food of the red-billed gulls and Hutton's shearwaters that breed there.
Kaikōura lies at the convergence of two major currents - the warmer north-eastern current that comes south from northern North Island, originally from Australia, and the cooler subantarctic current that flows up from below New Zealand and meets the other current at the Chatham Rise.
"Either of these currents could be responsible for pushing krill from deeper water up to the surface and then onto beaches, it's similar to the red tides you get in Otago from munida gregaria, or squat lobster."
The crustaceans have also washed ashore at South Bay, in Kaikōura.
Kaikōura resident Judith Hughey said she saw the krill on the beach last week, and it was quite deep and slimy in places. She said she had noticed visitors to the area were curious about what it was.
The crustaceans were pinky, red when they first washed ashore - before losing their colour.
"It has a really strong, fishy smell, I actually went for a swim in it and it has a pong like fish or dead seaweed."
She has owned a bach in the area since 1966 and said it was the thickest she had ever seen it, with plenty of birds - including white-fronted tern - feasting on it.
South Bay Fishing Charters owner Ian Croucher said there were acres of krill floating off the Kaikōura coastline.
He said the water temperature was slightly warmer than normal for this time of year, and had been fairly stable given the lack of southerlies bringing cold water north.
"Something is happening, maybe there is a lot of feed here. It all starts with the krill, the smaller stuff, then ends up with the bigger fellas."
Croucher said blue fin tuna had also appeared in the bay, with people coming from all over the country to chase the prized fish, with orca also spending more time along the coastline in large numbers this summer.