Warning that NZ's precious whitebait and long-fin eel stocks could be gone by 2050

When Kiwi fisherman Trent Robertson heard that the species of fish which was key to his livelihood was endangered, he retorted "there's plenty of them".

The fourth generation fisherman spends most of his days out on the river catching short and long-finned eels for export. An average haul a week is 300kg.

"A day of 100 to 150 kilograms is a good day, some days more, some days less," he said.

The whitebait season has kicked off, and with it comes a warning the delicacy is in decline. Source: Seven Sharp

He told Seven Sharp he loves eels, and occasionally bunked school to take lessons "on the river".

But Forest and Bird specialists paint a different story to Mr Robertson's perception that stocks were plentiful.

New research suggests that long and short-fin eels, and whitebait stocks, could be all gone by 2050 because of water quality and commercial over-fishing.

Mr Robertson doesn't agree with that analysis, telling Seven Sharp "nah, there's plenty of them".

Bird and Forest specialist Al Fleming however said numbers were declining, and that there needed to be a ban on the take of all long-fin tuna so they could recover.

He also said whitebait was actually the juveniles of five different fish - four of which were under threat due to water quality and over-fishing.

"What will happen is whitebaiters will see a slow decline and all of a sudden, they'll be gone," Mr Fleming said.

"Whitebait and long-fin eel are as Kiwi as our flightless parrot the Kakapo... people would be very concerned at the commercial sale of the Kakapo for the purpose of eating.

"So, we should not do that for our endangered freshwater fish."

Mr Robertson, who is also a whitebaiter, insisted there was only one number that was changing.

"The catches might be going down, but divide-up between however many people fishing it hasn't gone down," he said.

"Back in the day there used to be 10 people doing it, now there's 100... they're all still getting a feed or more."

In 1990, 20 per cent of 40 native New Zealand fishes were endangered, according to statistics obtained by Seven Sharp.

Now, around 75 per cent are in danger.