Longfin eel – on a path to extinction?

In mid-April 2013, the Parliamentary Commissioner for the Environment (PCE) Dr Jan Wright launched a report On a pathway to extinction? An investigation into the status and management of the longfin eel. The report warns Aotearoa¹ New Zealand that we need to stop commercial fishing of our native² longfin eels ❘ tuna³ (Anguilla dieffenbachia) or the species⁴ will face extinction⁵.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Tuna – longfin eel

Numbers of tuna – longfin eel (Anguilla dieffenbachii) have declined sharply, and the species faces extinction.

“No other action has the immediate potential to reverse the decline⁶ of the species. I hope that some means can also be found to reduce customary and recreational catches, should they be significant,” writes Dr Wright in the Commissioner’s overview of the report.

Multiple causes of declining eel numbers

A number of freshwater ecology⁷ experts have spoken out about the report. While most agree with the thrust of the report, some pointed out that decline in eel numbers is multi-causal, with habitat⁸ loss, erosion⁹ and run-offwetland drainage, death by turbine when swimming downstream and damming of rivers preventing migration. In a 2012 report on New Zealand eels, Dr Don Jellyman, Freshwater Biology and Fisheries scientist with NIWA wrote:

“While both eel species have been detrimentally affected by river channelisation, wetland¹⁰ drainage, etc being the species that penetrates furthest inland, longfins have been more affected by dams and weirs¹¹ than shortfins. Dams have historically impeded upstream migrations of juvenile eels (elvers¹²) although most large dams now have elver trap-and-transfer facilities whereby juvenile eels are caught at the base of the dam and manually transferred upstream. However, downstream passage of maturing adults is much more difficult to facilitate and passage through turbines is almost invariably fatal for female longfins. Estimates of total hydro mortality are of the order of 10–20% of the total commercial longfin catch.”

Conservation management criticised

Some experts feel that these other issues also need to be addressed, as does the PCE, who criticises both the Department of Conservation (who manage native species and work with councils on habitat issues) and the Ministry of Primary Industries (who manage the quota system) for their lack of effective action.

In a press release that accompanied the report, Dr Wright said, “I also have concerns about the management of the longfin, in particular the way the science is used and have also recommended that this is changed.

“DOC also needs to play a more active role in protecting this iconic¹³ species and work with councils to ensure habitat and fish passage pressures are reduced.”

Longfin eels’ life cycle

Part of the creature’s vulnerability lies with the eel’s own ponderous life cycle. The longfin eel can live for decades (at seaward spawning¹⁴ migration, males are typically around 25 years old and females are older than 40) and only breeds once near the end of its life, travelling thousands of kilometres north into the Pacific to do so. In a remarkable adaptation¹⁵, when it is ready to breed, the eel’s head becomes streamlined, its eyes turn blue and its belly turns silver in preparation for sea travel.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Erina with eel

Researcher Erina Watene-Rawiri prepares to release an eel back into the wild. She estimates this female eel was around 60 years old.

Fertilised eggs hatch into transparent¹⁶ larvae¹⁷ measuring just a few millimetres across. These larvae drift on the ocean currents for about 10 months back to New Zealand. By the time they reach our shores, the larvae have developed into transparent ‘glass eels¹⁸’. Between July and November, they migrate up estuaries¹⁹ and river mouths, slowly darkening in colour to become elvers. These elvers gather in shoals to swim upstream, taking months if not years to find a suitable habitat where they can spend most of their life. This life cycle leaves the creatures very susceptible to overfishing, habitat degradation and loss.

Need to set fishing quotas

In an interview with the Science Media Centre (SMC), Dr Angus McIntosh, Professor of Freshwater Ecology, University of Canterbury, said, “Eels are disproportionately important in New Zealand rivers because of their position at the top of the food web, so the imperilled state of longfin eel populations²⁰, highlighted in the PCE report, warrants action. It is concerning that some of the best evidence²¹ for longfin declines, a widespread and substantial reduction in their distribution, has not been given due weight in setting harvest quotas.

“I hope the agencies responsible for eel management implement the Commissioner’s recommendations. However, I’m concerned that the hamstrung state of the Department of Conservation, being further exacerbated by the current round of job cuts, will prevent it from doing so.”

Dr Roger Young, a freshwater ecologist²² from the Cawthron Institute, said the consistent lack of the smallest eels in samples from throughout the country is particularly concerning. “However, it is possible that this result may be influenced to some extent by the sampling method that has been used; electric fishing is generally less effective at catching very small eels. Despite this, I think the multiple lines of evidence indicating a decline in the eel population²³ is compelling.”

However, Dave Allen, Director of Aquatic Natural Resources Ltd, said the available evidence does “not provide a reasonable rationale to stop fishing completely, and there are more moderate options to further restrict fishing, while still ensuring sustainability, which are not entertained as a potential outcome” [for example, reducing catch limits].

“It is wrong to assume that a stock’s catch limit will always be caught in any one year – there are other factors that affect whether a stock is fished [such as international buyer demand]. In some contrast to northern hemisphere eel fisheries, the decline in national commercial catch for longfin, particularly in the North Island since 2004, is a reflection of MPI’s [Ministry of Primary Industries] active management intervention and the resulting significant reduction in the number of the commercial fishers and processing facilities.

“Maintaining an open mind to a range of research information is beneficial, and research providers and environmental advocates should actively participate in official science review processes, such as the MPI-convened Eel Science Working Group. MPI may need to explore alternative funding mechanisms to cater for a broader range of research indicators for this high-priority resource.

“As highlighted in the report, the combined inclusion of shortfin and longfin species within the same generic South Island eel stocks needs separation, so that more focused catch limits can be applied to longfin in the South Island. This would go a long way to providing the assurance that sustainability outcomes can be achieved on both a regional and a national basis.

“It would have been helpful if better incentives were identified for land and water users as it relates to habitat management. To expect that fishing interests should cease their activities for valued social, cultural and economic outcomes, for an indeterminate timeframe, because of inactions or actions of land and water users over many decades, does not provide the stimulus required for the latter to improve their performance.”

Rights: Public domain

Longfin eel

The longfin eel (Anguilla dieffenbachii) inhabits all types of water from tiny streams to the largest rivers, coastal and inland lakes, brackish (semi-salty) estuaries and lagoons.

The longfin can grow to 2 m long and live for over 100 years! The life cycle remains something of a mystery. The eels breed only once at the end of their life cycle. In autumn, adult eels leave the rivers and streams and head for the ocean. Scientists think the spawning grounds may be close to Tonga, but their spawning has not ever been recorded.

Considered a threatened species, longfin catch limits have recently been reduced and a maximum size limit applied to protect the large mature females.

The longfin eel has yet to be assessed for the IUCN Red List, but the New Zealand Threat Classification System lists it as ‘at risk – declining’.

Acknowledgement: Public domain

Ban on fishing longfin eels may not be enough

However, also in an interview with the SMC, Dr Russell Death, Associate Professor, Institute of Agriculture and Environment – Ecology, Massey University, said a ban on fishing doesn’t go far enough. “A moratorium on longfin fishing is an obvious first step. However, clearly more drastic steps will be needed to prevent its extinction. New Zealanders are proud of our efforts to conserve many of our terrestrial²⁴ species and it would be a tragedy to see our largest freshwater species disappear simply because it is not as cute and cuddly as many of our other conservation²⁵ treasures.

“In that regard, I would have liked to see some more prescribed suggestions of the way forward for its preservation. The agencies currently charged with the protection of eel appear to be failing, and we obviously need an alternative if we are to avoid losing another unique New Zealand icon²⁶.”

Dr Gerry Closs, Associate Professor, Freshwater Ecology, University of Otago, say the low numbers of juvenile and large adult longfin eels in recent catch data²⁷ from Otago and Waikato are particularly alarming and confirm too few longfin eels are surviving to breed. “Female longfin eels can take over 80 years to grow to maturity. Even if an eel fisher only returns to fish a site every 5 years, each longfin eel has to evade their nets on at least 10 occasions over their long life. The odds of surviving to maturity are minimal.

“Currently, the longfin eel is being managed into extinction by the government agencies responsible for their protection. A lack of action by the relevant ministers following receipt of this report would be wilful negligence. Closure of the fishery, essential if the species is to survive, will have little impact on the total catch of eels given that shortfin eel will still be available. In the longer term, sustainable²⁸ exploitation of longfin eels can only occur if either the North or South Island is permanently closed to commercial fishing.”