New Zealand's longfin eel is on a "slow path to extinction", warns the Parliamentary Commissioner for the Environment.
"There's nothing going on that's going to turn that around," Dr Jan Wright said.
Next month the commissioner will release her investigation into the plight of the vulnerable and declining species, which is commercially fished and feeds markets in Europe, North America and Asia - where native eels are on the verge of extinction.
Like kiwi and tuatara, the longfin - called tuna in Maori - is unique to New Zealand. They breed once in a lifetime that can stretch to 100 years then die after spawning around 2000km away in the Pacific Ocean's deep Tonga trench.
The migration begins in April when males head off first, followed soon after by females. The spawn site is thought to be between Fiji and New Caledonia.
Larval eels then drift on ocean currents and wash ashore back in New Zealand, where they make their way up rivers as elvers before reaching maturity and breeding often decades later.
Massey University freshwater ecologist Dr Mike Joy said moves to protect the longfin needed to be made now because no-one knew the threshold at which declining breeding numbers would make the species' survival untenable. "We don't have the science and we're playing with fire when we carry on harvesting them," he said.
Fishing quotas for longfin eel differ in both islands. In the north, a commercial catch of 82 tonnes is allowable, with a further 47 tonnes for customary catches and 33 tonnes for recreational catches.
In the South Island, the quota for longfins is combined with the less vulnerable shortfin eel - at 421 tonnes for commercial, 107 tonnes for customary and 11 tonnes for recreational.
- © Fairfax NZ News
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