The longfin eel could soon be extinct, ecologist Dr Mike Joy has told an international conference.
The species only mates once, at the end of its life, and there could already be fewer longfin eels than were needed to sustain a population, he told the Australasian Wildlife Management Society conference at Massey University in Palmerston North.
The eels live in freshwater around New Zealand before travelling to Tonga to breed at the end of their life. Longfin eels could live for more than 100 years, Dr Joy said.
Because females were larger and there were minimum size limits for commercial fishing, a disproportionate number of females were caught, he said. One sample of 500 eels recently conducted found 490 of those examined were male.
"There are few females left in commercially fished areas," Dr Joy said.
Because of the risks eels faced returning to New Zealand after hatching in Tonga, it would be possible that a tipping point would be reached where there were not enough eels left to sustain the population.
"There won't be a natural decline, there will be a mass extinction," Dr Joy said.
The way commercial fishing was carried out in New Zealand was unsustainable, he said. Commercial fishers could not return to the same waterways year after year but instead looked for new areas to fish, including on the conservation estate.
Eels were too easily caught, Dr Joy said. Five nets could be put out in one night and 90 per cent of the eels in the area caught, even without bait. There was a quota for eels but this had never been met because commercial fishers could not find enough eels to reach it.
The degraded state of waterways was also a factor impacting on eels, as was the loss of their wetland habitat and the damming and blocking of streams and rivers which further reduced their habitat.
Longfin eels were potentially the largest eel species in the world, but were classed as threatened and declining, Dr Joy said.
There was a Ministry of Primary Industries review into eel stocks under way but it was too narrow in scope, he said.
For example, recommendations around future management of the longfin catch was outside the scope of the review.
"Sixty-eight per cent of our freshwater fish are listed as threatened," Dr Joy said. "At least five of our threatened fish are also commercially harvested."
- Manawatu Standard
Is New Zealand's airport security stringent enough?Related story: Risky objects bypass Wellington Airport security