Longfin eel numbers uncertain

05:50, Dec 06 2013

The size of the longfin eel population is highly uncertain, but there is a high probability it has been substantially reduced, an international panel says.

After a recommendation from Parliamentary Commissioner for the Environment Dr Jan Wright, the panel of three experts reviewed information used to guide eel fishery management, particularly that of longfin eels.

Most data available on the eels had been collected and analysed in relative isolation. Depending on the data used and the approach taken, different conclusions had been reached, the panel said in a report published today.

"What appears to be lacking is an integration of the different information sources, a comprehensive assessment addressing all potential impacts/threats to the eel – informing the managers on the status of the stock as well as its resilience to human impacts in inland habitats."

Assessment of longfin eel stocks indicated there had been a general decline from the early 1990s until the late 2000s. Catch per unit of effort data suggested that since the late 2000s there had been a slowing and perhaps even a halting of the declines.

Electric fishing surveys – in which fish are stunned by electricity – indicated relatively stable abundance from the late 2000s.


Elsewhere in the world, the stock of northern temperate eels – in Europe, America and Asia – had declined steeply.

A growing number of studies were looking at potential causes of the decline, but there was no hard evidence or shared view.

It was quite unlikely the New Zealand longfin eel stock had already experienced a decline as dramatic as that in the northern temperate eel stocks, the panel said.

European countries and US states were making comprehensive assessments of their parts of the eel stock, and a similar assessment could be carried out in this country.

The panel suggested additional methods of assessing eel numbers that might be used in New Zealand.

They included sampling of glass eels – those in their first year in freshwater – at mouths of rivers, marking and recapturing, and monitoring of eel deaths as a result of human actions other than fishing.

The panel also said the eel monitoring programme was deficient because it failed to systematically monitor migrant eels. As a result, spawning escapement – adult fish returning to spawn – was unquantified.

Panel members were research ecologist Dr Alex Haro, of the US Geological Survey, fisheries scientist Dr Willem Dekker, of the Swedish University of Agricultural Research, and New Zealand-based Nokome Bentley, of Trophia Ltd, which is a co-operative of independent fisheries scientists.

The Ministry for Primary Industries said its eel science working group would discuss the review panel's recommendations this month.

Primary Industries Minister Nathan Guy would consider management actions in light of the panel's report early next year.

Fairfax Media