Last spring I spent a few weeks exploring New Zealand’s South Island with local friends. I was dazzled by a land of clear, intensely blue waters. I was astounded that on mountain hikes in their Alps, I could even drink water freely and safely. At one stop at the high alpine Lake Rotoiti, I became curious about the graceful, velvety, blue-eyed eels that met my gaze from a pier over the water.
I grew up hearing tales from my older sister of night eel-fishing parties on the rivers in Virginia where I spent my childhood. And here were eels in New Zealand, taking gulps of bacon dangling from children’s fingers as the children lay at my feet on the sun-warmed planks above the lake’s edge. When I asked my friends about these eels, they laughed, recalling tall tales and encounters with the longfin eels during their childhood. They exclaimed that “heaps of eels” have always been around, but that they never really thought much about them. “They’re just there, mate.”
When I returned home to Tucson I began to do some exploring of the virtual kind. I was astounded at what I discovered about the eels and disillusioned about their supposed land of clear, clean water. It turns out that these fish are ancient creatures with a peculiarly wonderful life cycle. But their days of being common, or of even existing at all, may be coming to a close. So in returning to New Zealand three months later, I decided to meet with marine and freshwater scientists from such groups as the Ministry of Fisheries (regulators of the country’s fishing industry), the government’s Department of Conservation, Massey University, and Forest and Bird (the Royal Forest and Bird Protection Society of New Zealand, a privately-funded conservation organization locally called Twig & Tweet).
I learned that over 100 million years ago, the ancestors of these freshwater longfin eels (Anguilla dieffenbachia) likely lived their lives in the ocean, and eventually found some protection by entering the freshwater ecosystems of what would later be called New Zealand. Scientists believe they gradually adapted to spending more and more of their lives farther and farther inland, until they became what they are today: an unusual fish species that spends its entire adult life in lakes and streams, but is still bound to the ocean for one critical life phase. Longfin eels must migrate far out to sea to spawn, and the young must then find their way back upstream and inland to live their adult lives. This incredible life migration accounts for why this particular species could become extinct in short order. First, the female eels must live between 30 and 100 years before they are able to reproduce, while the males take 15 to 45 years to reach reproductive maturity. Since many eels won’t live that long, only a small number of adult eels actually migrate down from the lakes each fall. And due to modern human obstructions, only a fraction of these migrating eels now make it to the deep sea trenches to mate.
You can imagine the changes to New Zealand’s waterways since the Industrial Revolution. A century ago there were no imposing hydroelectric dams. A century ago only a few people (mainly the aboriginal Maori people, to whom the eels are a sacred part of culture and tradition) were fishing with handmade hinake nets in order to feed only their own communities. A century ago wetlands had not been drained. A century ago the waters were free of choking pollutants like pesticides and fertilizers that run off from farms. Today, if a two-meter-long migrating female – her body full to bursting with millions of eggs – is lucky enough to be gently “caught and carried” over a dam by humans, she must still make her way past commercial traps that catch unsuspecting eels by the tons each year. She must still struggle over many smaller dams, across large expanses of dry sand and rocks, and through chemical-laden water. And all that even before reaching the Tasman Sea, where she will begin an ancient journey to the deep sea trenches some 4,000 miles away!
Before the adult eels undertake this epic journey, their bodies undergo dramatic physical changes that will allow them to survive. First, the eels’ eyes grow larger and more sensitive to light. This lets them see better while they travel by night in order to avoid dangers such as large predators. Next, they stop eating. For several months their traveling bodies must subsist without food, for there is no room for it with the massive amounts of egg and milt (sperm) that fill their body cavities. Then, as they reach brackish water where the rivers meet the sea, they rest a bit and allow time for their gills to change so that they are able to get oxygen from saltwater rather than fresh.
Scientists are just now taking steps to understand precisely where the eels go to mate as well as the actual nitty-gritty of their mating ritual. It has long been believed that these longfins all meet up in the Tonga Trench. About 6 miles deep, it is located just to the east of the Tonga Islands. In just the past several years scientists have been radio-tracking these superfish. They now think the eels may also travel to other deep places to mate, including eastern Fiji Basin. We know that the eels meet in these trenches, mate via external fertilization, and die.
But, a scientist from the Department of Conservation gave me the real, brutal details. It seems that the longfins form a violent mass of reproduction. As they have evolved no other way to release their gametes (sex cells), the swarm of eels begins to knock and bash into each other, bursting apart and releasing their egg and milt to swirl and mix and join in the water as the old, battered eels die.
Soon the tiny young become part of the smallest creatures in the ocean. During their time at sea, the larvae (leptocephalli) are unable to swim for themselves, and thus depend upon the seasonal ocean currents to drift all the way back to the edges of New Zealand. As they travel, like a tide of shimmery leaves, they begin to morph into something that looks more like an eel, but is transparent. This stage, known as the glass eel, is colorless to escape the view of predators. The glass eels begin to darken, and so become “elvers” when their tube nostrils sense more freshwater and less saltwater around them. Soon the elvers bunch up and enter the freshwater waterways under the cover of darkness. They travel by night, like their parents did, and their scaleless bodies wiggle backwards to hide between and under rocks during the bright days.
When a waterless area must be crossed, the eels wriggle over the surface of land and actually breathe through their skin. But they can only sustain this for a short time, while their skin remains moist, an especially tricky predicament because New Zealand has lost 90 percent of its wetlands since the first Europeans arrived.
Voracious predators, the growing eels will eat anything they can catch, grasping prey with rows of slanting, peg-like teeth. Exposure from their burning hunger allows the elvers to be caught in large numbers and exported as a delicacy to European and Asian markets. The eels that manage to avoid such capture continue their upstream migration.
Elvers measuring less than five inches can climb steep, wet surfaces, up to 100 feet tall. Many of New Zealand’s damns, however, are higher – and larger elvers cannot climb vertical walls at all. When the eels cannot crawl over or find their way around the dams, the eels starve or are eaten by predators that include invasive species like perch and rats. Rats wait by the edges of dams and snatch migrating eels right off the dam wall. Longfins have lost half of their habitat to dams.
Most of these hard facts were shared with me one wet, wintry day in Nelson, New Zealand, as I sipped coffee with Dr. Mike Joy, a fish and freshwater biologist from Massey University, on New Zealand’s North Island. It seems Dr. Joy is swimming upstream himself as he tries to get others with influence to listen to the facts that show the precarious state of the eels. I listened as he explained that many other endemic, freshwater fish in New Zealand are in similar danger due to the rapid degradation of the country’s freshwater ecosystems. If he could make people aware, and have the Ministry of Fisheries ban commercial longfin eel fishing, he would feel somewhat successful.
I was glad I could tell him that I heard, and was hard at work writing and illustrating a children’s book about the eels to help raise awareness. Then he mentioned that the American eel (Anguilla rostrata), of Atlantic watersheds, is equally amazing – and equally challenged.
As I walked back to my hostel, I had to shake my head and laugh at how we often seem to know and understand the least about the intricate life that in our own backyards and streams. I suppose a trip to my sister’s home along that river in Virginia is about due. I will listen to her fishing stories. I will look into that old familiar water and try to really see – before it is too late.
Stephanie Bowman most often resides in Tucson, Arizona. She is an educator, artist, and writer working for the environment. Stephanie serves on the board of directors for Reptile and Amphibian Ecology International, where she develops educational outreach presentations that connect rainforest ecology with the ecology in our own backyards. She will be leading several high school students on a scientific expedition to the Amazon rainforest this summer.
This October, Stephanie plans to visit New Zealand schools with a longfin eel outreach program that utilizes art to teach teh science of the eels and freshwater ecology. Contact Stephanie with questions or offers of assistance and funding for the eel outreach program.