Key Points:

We would like to write a business proposal for the commercial harvest of little spotted kiwi. We imagine they could make $10,000 each on overseas exotic foods' black markets. Surely a good idea, as it would make money and create jobs. Fortunately for the kiwi, we doubt our proposal would be accepted due to its endemic and endangered status.

Contrast this with another endemic and endangered animal, the longfin eel, which lives five times longer than the kiwi and reproduces just once at the end of its life.

Longfin eels, already driven to low numbers by loss of habitat and pollution, are commercially fished mostly for export to Europe and Asia. As a result, they are on the verge of extinction.

Both species of New Zealand eels - longfins and shortfins - have been commercially fished since the 1960s. Eels are caught in traps, a technique that catches more than 90 per cent of all eels in a stretch of stream.

Commercial catch levels peaked in the 1970s, and then began a decline, especially in longfins. Catches have declined further since eels were drafted into the Quota Management System (QMS) earlier this decade.

Quotas are based on previous catch data, so it is not surprising that these so-called commercial limits have not constrained the number of eels being killed in any way.

In fact, the Total Allowable Commercial Catch (TACC) for longfins has never been met in any area. The TACC for shortfins has been met once, in Taranaki in 2004.

Eels are a New Zealand icon. They are often very old - shortfins can live for up to 60 years and many large longfins are over 100 years old, although there are few of these left as they have been mostly been fished out.

Females of both species live longer and grow more slowly than males. Because commercial fishing selectively removes the larger females, there are relatively few of them left, which has dire repercussions when it comes to breeding time.

Eels spend almost all their lives in freshwater but move to the ocean to reproduce. They migrate to the deep trenches around Tonga, where they spawn collectively, then die. The newly hatched larvae drift on ocean currents back to New Zealand where they will spend the next two to 10 decades.

Like all our native freshwater fish, eels have been subject to severe impacts since human colonisation of New Zealand started. Destruction of wetlands, abstraction of water from streams, pollution and sedimentation have affected native eels in the same way that forest removal has affected native birds. Barriers to migration, such as dams, culverts and weirs, have effectively cut off most suitable remaining inland habitats.

Here we have native species under threat from habitat loss, just like so many others in our New Zealand refuge. But instead of protecting them and investing huge amounts of time and effort into predator control - like we do with endangered birds - eels are being systematically exterminated for profit.

Every bit of data gathered on eels in New Zealand points to a looming catastrophe - a greater than 75 per cent decline in longfin juveniles returning to here, skewed sex ratios with few females left, and a huge drop in eel size and catch rates.

Due to the unique reproductive biology of eels, we will not see the gradual decline we do with other species, but a sudden crash.

This has already happened in the Northern Hemisphere, where the American, European and Japanese eels are all near extinction, having succumbed to the same habitat loss, pollution and overfishing as our own. We must not let eels go extinct.

For once, there is an easy solution - just stop commercial eel fishing. No fisheries model can manage a species that breeds only once at the end of a long life. The Ministry of Fisheries manages this fishery for the benefit of a small commercial fishery, employing fewer than 100 people.

These few exploiters of native endangered fish are putting at risk an irreplaceable species.

* Amber McEwan (a student) and Dr Mike Joy are at Massey University. Dr Joy is a senior lecturer of environmental science/ecology with the Ecology group Institute of Natural Resources.