New Zealand Longfin Eels: Freshwater Species of the Week

New Zealand longfin eels may not be pretty, but they are ecologically important. Photo: Gusmonkeyboy, Wikimedia Commons

New Zealand’s large, slow-growing longfin eels (Anguilla dieffenbachia) are on a “slow path to extinction,” according to an April report by the parliamentary commissioner for the environment.

The commissioner has now been joined by a number of scientists in calling for a ban on fishing of the eels, since their numbers have been declining in both the North and South Islands.

University of Otago ecology professor Gerry Closs told the Otago Daily Times that a lack of government action after the commissioner’s report would be “willful negligence.” Closs added that fishermen could still sustainably harvest New Zealand’s other native eel, the shortfin, which is much more abundant.

The New Zealand advocacy group Forest and Bird has also called for protection of the longfin eel, urging that the country avoid losing another unique species. In addition to fishing pressure, the eels have faced degraded habitat and lack of access to former living spaces thanks to dams.freshwater species of the week

Complex Lifecycles

Like many eels in North America and Europe, New Zealand longfin eels are catadromous, meaning they spend most of their lives in freshwater, where they can often swim quite far inland. But when it is time to spawn, they head out to sea (see our profile of European eels).

Longfin eels take a long time to reach maturity, typically between 20 and 60 years, although 80 years isn’t unheard of. The oldest living longfin recorded was 106. The eels grow very slowly, only one to two centimeters a year.

Females are longer, up to 61 inches (1560 millimeters), and can weigh up to 53 pounds (24 kilograms). Males grow up to 29 inches (735 millimeters) and tend to not live as long.

The eels reproduce only once in their long lives, which is part of why their numbers have been in decline. When they are mature, they leave their freshwater homes and swim thousands of miles out to sea, toward Tonga. Females produce one to 20 million eggs, which the male fertilizers.

The larvae drift back to New Zealand on currents, in a process that can take up to 15 months. When they reach estuaries, they change into glass eels, small transparent creatures. They add bulk and coloration over time until they reach a stage called elvers. When ready, elvers swim upstream, where they grow into adults.

The elvers are a plucky lot that are known for their ability to climb their way upstream, using surface tension as a springboard. They have been observed scaling a nearly vertical section that was 141 feet (43 meters) tall.

Longfin eels have long been revered by the Maori, who have used them as an important food source.

Pointing Fingers

In 2012, it was revealed that some pet food companies turn longfin eels into chow. This outraged conservationists, who pointed out that the animal has the same status as the iconic kiwi.

Bill Chisholm, a spokesperson for commercial eel fishermen, told the Otago Daily News that his relatively small industry (responsible for 100 jobs) isn’t responsible for the declines in eels. Voluntary measures the fishermen have taken are working, he said, and weren’t reflected in the commissioner’s report.

Forcing eel fishermen to ”go bust” while eel habitat is damaged by ”hydro dammers, water abstractors and polluters is ridiculous,” he told the paper.


Brian Clark Howard is an Environment Writer and Editor at National Geographic News. He previously served as an editor for and E/The Environmental Magazine, and has written for,,, Yahoo!, MSN, Miller-McCune and elsewhere. He is the co-author of six books, including Geothermal HVACGreen Lighting and Build Your Own Small Wind Power System.