Eels - slimy denizens or magnificent beasts?

An article about New Zealand freshwater eels

I was pleased with my evening’s catch -- two fat pan-sized rainbow trout. One each for breakfast. Now to clean the catch and hit the sack. The night was warm, still and clear, with stars galore; tomorrow would be another beautiful day. Nothing could spoil the weekend, I thought. Well, almost nothing: I was gutting the second fish when suddenly, wham! it was snatched away from under my nose. My hand was nearly dislocated by the jerk. I switched on my torch to see ... a great black shape making off with my catch, swimming sinuously and powerfully out over the drop-off. A howl of rage cut the night in half ... Bloody eel!
Eels. We all have opinions about them, and not usually very nice. “They’re slimy ... They stink ... They give me the creeps ...” No fish and game council ever spent time gazetting regulations governing a recreational fishery for eels -- minimum sizes, catch limits or seasons. Who ever heard of a catch-and-release area for eels? There are no eel posters on fishermen’s walls; no eel fishing clubs. And (although the Maori might have plenty to say about it), I’ve never once seen any of the opinionated commercial-fishing bashers in any fishing magazine complain about the commercial eel fishermen stuffing up the resource for everybody else ...
Well, I’m here to say that’s an ignorant attitude. Eels are magnificent beasts. I love them. Except perhaps for an hour or so after that one flogged my breakfast (Yes, I had muesli instead, and am not ashamed to admit it.) Eels are wonderfully adapted to their environment and deserve just as much respect as any other living creature. What’s that? I hear howls of derision. Very well. Turn the page if you wish. Or read on, and perhaps you’ll come to see them with a new respect. Even affection.
We have two types of eel in New Zealand waters -- long-finned and short-finned. They are very closely related and the main difference is in size. Long-finned eels (“longfins”) are recognised by the fact that the dorsal fin extends much further forwards than the fin underneath. Longfins live in estuaries, rivers and lakes all the way from the coast to the mountains. They grow to more than 20 kg in weight and nearly 2 metres long. They prefer stony rivers and clear water. These are the huge black eels we see in wilderness rivers and back-country lakes, for example Lake Rotoiti and its feeder rivers, at the top of the Buller catchment. Longfins are unique to New Zealand.
Short-finned eels (“shortfins”) have the dorsal fin only slightly longer than the fin underneath, rarely grow larger than a couple of kg in weight and are not more than a metre in length. Shortfins also occur in New South Wales, Victoria and Tasmania.
Both longfins and shortfins vary a lot in colour, with grey to black most common. Yellow or silver-bellied eels are usually longfins but either species may be this colour. The early Maori had many names for eels depending on colour and pattern, and much folklore associated with these.
However repellent eels seem to some, the fact is they are beautifully adapted to live in all kinds of freshwater environments. They can fit themselves into any nook or cranny that is large enough, even under loose stones in river beds. They have small compact heads, and a slender flexible body covered with only very tiny scales embedded in slime, which means they are extremely flexible and able to move through very tight spaces. They lurk rather than swim actively like trout most of the time, so they use little energy. Eels can live for long periods without food and can tolerate poor water quality-- muddy or polluted water with just one part per million of oxygen, absorbing it through their skin as well as their gills. Eels usually move very slowly, which conserves energy and reduces the amount of food they need. But they can also swim very fast, either backwards or forwards. They can even wriggle for considerable distances over land. Eels hunt by smell rather than sight, so they are quite at home in the dark or in muddy waters, and will eat practically anything of animal origin that they can get their mouths around -- freshwater insects, snails, worms, fish and carrion. They have large distensible stomachs, so they can feed heavily and intermittently as opportunity presents, eg. gorging on worms, insects and spiders when land is flooded, or grabbing hold of a large carcass and spinning round to tear off chunks. Big eels take larger prey such as fish and crayfish, and even the occasional small bird, while smaller ones mostly eat insects and snails.
Small eels are eaten by trout, shags and other water birds, but once an eel reaches a good size it has virtually no enemies other than humans. In fact eels are so successful that they make up 80% of the total biomass of fish in many waterways.
Eels are not territorial, but some may be home-ranging. Tagged eels in lakes have been known to travel overnight right across the lake, but this is probably feeding behaviour and nothing to do with migration. Being wide-ranging helps ensure eels are widely dispersed throughout all their available habitat.
Eels can be aged by counting annual rings on their earbones. and when this is related to their length and weight some unusual facts emerge. Unlike most other animals, which grow fastest when they are young then slow down or stop growing when they are older, eels keep on growing at a fairly steady rate throughout their lives. The growth rate also varies a great deal from one place to another. For example, some enterprising soul introduced a few eels into Lake Aniwhenua, which is well known for being a very rich feeding ground, and one of these reached 105 cm long at the age of 12 years. In contrast, a 10-year-old eel from the lower Waikato was just 32 cm long, and a 30-year-old from the south branch of the Waimakariri was only 44 cm long.
Eels also reach a phenomenal age. One from Lake Rotoiti in the Nelson province was more than 100 years old and 1.2 metre long. When you consider that beast was already cruising around the lake in the nineteenth century, at one time swimming about under the light of Halley’s Comet, and already quite a large animal when World War 1 broke out, it is impossible not to feel some respect for such a creature, or at least hold it in awe. Think about this: a great many of the eels caught are considerably older than the people that catch them.
All freshwater eels migrate to the sea to spawn. They go only once and never return. Shortfinned eels migrate at around 14 years (males) and 20 years (females); longfinned eels at more than 20 years (males) and 30 years (females), but some stay in fresh water for a lot longer, often more than 60 years. This is a much higher age of reproduction than for any other kind of fish in our waters, except perhaps orange roughy. Think about this: most eels don’t reproduce till they are older than many humans start having babies.
When it’s time to go and do their thing, the males migrate downstream before the females, probably because they need to set off sooner in order to arrive at the spawning grounds at the same time.
There is a myth that giant eels are sterile animals that have never felt the urge to migrate, just stayed on and grown bigger and bigger. But in fact they are big females that have not yet migrated, though they must be nearly ready to do so.
Before migrating, eels change in shape. The head becomes more pointed and the eyes enlarge. They cease feeding. These changes adapt them for making a journey through oceanic waters.
In nature, some creatures rely upon producing a very few young and taking great care of them, while others produce larger number of young and leave them to their own devices. Eels are an extreme example of the latter sort. A large shortfin eel will produce 4 million eggs; a large longfin up to 25 million. That means as many as 99.99996% of a big eel’s progeny can die yet her genes will still be perpetuated.
Yet even an average-sized male eel less than a kilogram in weight produces plenty of sperm with which to fertilise all those eggs. This helps to explain the size difference between female and male eels, and the difference in lifespan. Male eels don’t need to be so big in order to produce enough sperm; but female eels need to be as big as possible in order to produce lots of eggs. The main limiting factor is that male eels need to be big enough to have enough stored fat to fuel them on the journey across thousands of kilometres of ocean.
We can only imagine what the scene must be like in the ocean depths when hundreds of millions, even billions, of eels get together for that last great fling before they die. (To some, this may be a subject best not dwelt upon, as it could cause nightmares!) By the time they have travelled all that distance the eels are probably very skinny, almost just big wrinkly sacs of eggs with a head at one end and a few emaciated muscles left with which to swim. Spawning in huge groups in the ocean has its advantages in helping to maintain genetic diversity and avoiding inbreeding. Not many eel larvae have been caught by research boats, but from the few that have it seems longfinned eels probably spawn northeast of Tonga, and shortfinned eels north to northeast of Vanuatu. With modern technology enabling radio-transmitter tags to be attached to fish then tracked all over the ocean, it is very likely we will have a better understanding of this in the next few years.
Initially shaped like small transparent leaves, eel larvae (called leptocephali, meaning “leaf-head”) are readily carried along on the ocean currents, where they feed on small plankton. (Most of them too are eaten.) They start to arrive in the New Zealand region probably in the spring of the year after they were born, at which time they are about 6 cm long. As they move inshore they become glass eels, changing shape to adapt themselves to swim properly by wriggling along instead of passively drifting. In this process they lose about half their weight and become shaped like long slender whitebait.
Vast numbers of glass eels have been seen on the big rivers. One continuous shoal was seen lasting 3 days and 2 nights on the lower Waikato River. Glass eels can climb wet surfaces vertically, sticking on by surface tension, and even up overhangs until they reach a size of 12 cm long. Waterfalls, culverts and weirs can’t stop them, but big hydro dams or pipes that discharge from a height are usually an effective barrier. As they darken in colour they are called elvers, and these are like miniatures of the adult.
But even after all this breathless David-Attenborough-style stuff, I can tell many of you still aren’t impressed. A psychologist will probably tell you that your continued revulsion is because they remind you of snakes, and that this goes right back to the Garden of Eden in the Bible. Or Sigmund Freud with his (gulp) phallic symbols: who could compete with a 20-kilogram longfin in that department? Eels are also slimy and don’t smell very pleasant. When you catch them they are hard to kill, and go on writhing even long after they’re dead. Many of us have stories to tell of fishing at night and stepping on an eel, or having one swim very close by -- scary, perhaps, but not dangerous. There are even stories of eel attacks, though most of these are fanciful. Worst of all are the dyed-in-the-wool so-called sportsmen who cling to outdated theories that eels reduce trout numbers. Eels do eat some trout, but the reverse is also true. Research has shown that eliminating eels from a trout stream leads to more but smaller and skinnier trout -- what sportsperson would want that? This is confirmed by the fact that most great trout waters have eels as well -- the Motueka, Karamea and Mataura to name just a few.
According to one Maori tradition, eels originated from among the children of Hine-moana (Ocean woman) and her husband, a man named Kiwa. In the South Island it was said that Tuna, the eel, had come down from the sky because the upper regions were too dry. After the eel seduced Maui’s wife Hina (or Hine), Maui took his vengeance by digging a trench, and as the eel swam along it Maui chopped him to bits. From these pieces sprang other life forms, including the conger eel, vines (from the eel’s thin tubular nostrils), and many other plants, including trees like rata that have reddish wood and are supposed to have formed from the blood. Similar stories about eels occur in other parts of Polynesia, and the persistence of these stories underscores the importance of eels to the indigenous peoples.
But it is probably very difficult for us to realize today quite just how important eels were to them in the past. Eels were the most reliable and widespread food source of all, and one of the most abundant. Practically every stream, lake or swamp was teeming with them. They could be easily caught by a wide range of methods, even with the bare hands. Eels could be caught when the weather was too bad for sea fishing or hunting, and provided a backup if crops failed or if people were driven away from their homes. Eels didn’t all migrate every year like certain birds and sea fish, so they could be found year-round. Travellers and war parties must often have staged their journeys so at nights they would often camp right next to a reliable food source. Along the coast, eels were extra plentiful in autumn as they migrated to the sea, and provided a reliable food store that could be laid in for the coming winter.
And eels were extremely nutritious with little waste. Practically all an eel’s body is meat. The bones and head are small, and the flesh is rich in fat. An eel would go a lot further than the same weight of fern root or birds, and was probably more easily obtained.
Eels were even important strategically. For example, the pa at Kaiapoi could not be starved out by a siege party as it was surrounded by a lagoon with its own ready food supply. Small wars were fought over the ownership of lakes and marshes which provided rich eel resources.
Today, although of course that traditional fishery continues, most eels are caught commercially, using fyke nets and hinaki (Maori-style eel pots). The fishery is largest in lake Ellesmere (Waihora), near Christchurch. At present the commercial eel fishery yields about 1500 tonnes a year, down considerably on the 1976 peak when they briefly ousted snapper as the number-one species in terms of tonnage caught. The value of this is about $10-12 million a year.
Eels will soon be brought under the quota management system, but already there are a number of controls in the fishery. No new licenses are issued and the areas each fisherman can work are restricted. Processors won’t buy eels below a certain size, which is if anything a better restriction than a minimum size set by law.
Eel fisheries will need to be closely controlled to safeguard the resource in future, because eels are so slow-growing and important to both traditional and commercial fisheries. Their environment needs to be protected too; for example more than 90% of the area of wetlands on the Waikato has been lost by drainage. Pakeha have always regarded farmland as more valuable than wetland.
Still think eels are disgusting? If so, you’re incorrigible, and it will serve you right to read this next bit. New Zealand is home to only a small fraction of all the world’s eels. There are 14 more species and they are spread around most of the world. The 3 northern hemisphere species, occurring in North America, Europe and Japan, are commercially the most valuable. European and American eels spawn in the Sargasso Sea on the western side of the Atlantic and the larvae are carried by the Gulf Stream up the east cost of America and across the Atlantic.
So there you are. Like ‘em or hate ‘em, even right now, billions of longfin and shortfin eel leptocephali are drifting out there in the western Pacific, getting ready to turn into glass eels, which will become elvers, swim up your favourite fishing river, insinuating themselves up to your secret possie. Some of them will turn into whoppers which you might want to curse at when you see them swim languidly past, or when they steal the trout that’s meant to be your breakfast. But remember also that while they’re small, some will be tucker for that big double-figure fish you dream about. And some of them will help control the trout population by weeding out the sick or weakened ones, so there won’t be so many slabby ones and the big trout will thrive. Other eels will help someone make their living, or give people who appreciate them (including some Pakeha as well as Maori) a real buzz to catch and eat. Remember too that some of these eels will probably outlive most of us. Finally: they’re part of the natural way of things. Live and let live.
Acknowledgements: Much of the material for this article is based on a seminar presented in 1996 by Dr Don Jellyman to NIWA staff in Christchurch, titled “The secret life of eels”, and reproduced with his permission. The Maori myths quoted are from The Illustrated Encyclopedia of Maori Myth and Legend, by Margaret Orbell, published by Canterbury University Press. For more detailed information about eels, see New Zealand Freshwater Fishes, by R.M. McDowall, published by Reed.

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