Longfin Eels of New Zealand: an interview with Dr. Don Jellyman

While out on the water, I found myself with the most fascinating and, I must admit, frightening creatures. They were long and brown and thick and had the scariest mouths. I knew what they were, eels obviously. But little did I know that learning about this creature would be one of the highlights of my trip. I had the opportuntiy to interview Dr. Don Jellyman, an expert on eels. This is a recap of what I learned. It truly fascinates me and I hope you find it interesting as well!


I had the opportunity to interview Dr. Don Jellyman, an expert on eels in New Zealand.   Don grew up by a river in Blenheim, NZ and became interested in fishing at a young age. At the time there was a bounty on the native eels because they were thought to be bad for the introduced trout fishing. In the 1930’s there was an eel destruction campaign to catch and kill these eels. Later, scientists discovered that although eels are predators to small trout, they actually improve trout populations. This campaign has since been ceased and now measures are being taken to protect eels.

Don got a doctorate degree on eels in 1974 and has since dedicated his career to study these interesting creatures. New Zealand has three different types of eels: the longfin eel, the Australian mottled long fin, and the shortfin eel.  The longfin eel is the only one endemic to New Zealand and Don and other scientists have concerns for their well-being.

Eels are top predators in New Zealand lakes and rivers; they play an important scavenging roll. They also make up to 80% of the biomass of freshwater fish in most rivers, largely due to their size compared to most native fish which are quite small.

Eels have an opposing spawning structure to salmon. While salmon spawn in the rivers and then swim downstream to the ocean to live their lives, eels are born in the ocean, swim upstream as baby eels (known as glass eels), live their lives in freshwater and then at the end of their lives return to the ocean to spawn. They only spawn once during their lives. Eels can live for a very long time, scientists have found eels over a hundred years old.

Don and other scientists have concerns with the number of glass eels swimming upstream, finding the numbers lower than they would like. The major threat to longfin eels are hydrodams. When mature eels swim downstream to the ocean to spawn, they often find hydrodams that are very likely to chomp them up and kill them. Glass eels face similar threats when swimming upstream. Efforts are being made to catch eels before the dams and relocate them to the other side.

Another threat to eels is the loss of willow trees. Eels depends on shade from willow trees and without the shade they cannot exist. Eels require refuge areas to avoid sunlight, and willows provide shade but also hiding areas among their root systems; if there isn’t suitable “cover” like this, there won’t be any eels.

Historically, eels served a very important role for Maori culture. In the absence of land mammals, Maori depended on eels (or as they call them tuna) for food. Maori built sophisticated handmade traps that caught the downstream migrating eels.

Currently, Don and other scientists are catching and tagging eels and watching where they travel to spawn. Some eels have been found as far away as Fiji. The miraculous thing about longfin eels is that the glass eels always swim from the ocean wherever they may be to New Zealand. It isn’t quite known how they know to come to New Zealand as baby eels, but it is a wondrous phenomenon.