River Monsters

by Jeremy Wade

  The breakthrough came in 1897 when the Italian biologist Giovanni Grassi announced the capture, from the sea near Sicily, of a male eel carrying sperm. He also discovered something else: swarming in the sea were transparent creatures, shaped like willow leaves and known as leptocephali (Latin for “thin heads”), which everyone else assumed were simply small, strange fish that didn’t grow very big. But Grassi suspected they were the larval stages of something else. He noted that the number of vertebrae—115, give or take 1 or 2—matched that found in freshwater eels. On keeping some under observation in an aquarium, he subsequently observed the metamorphosis of thin-head into eel.

  However, all the thin-heads that Grassi found were fully grown, about three inches long and almost on the point of metamorphosis. Because there were no smaller ones here, they must have come from somewhere else, but nobody knew where. Danish scientist Johannes Schmidt was the one who finally discovered the eel’s breeding grounds, three thousand miles from Europe in the Sargasso Sea, a deep, still patch of water north of Puerto Rico and east of Florida. He did this by towing fine nets in different areas of the north Atlantic until he located the region where the smallest thin-heads were found. These were one-fifth of an inch long (five millimeters), and for the purposes of general textbooks, the European eel’s life cycle is now a closed case—except nobody, to this day, has ever observed eels breeding in the wild.

  The first eels that ventured into fresh water are thought to have evolved in the ocean near present-day Indonesia. This population split and dispersed on the changing ocean currents as the proto-continents drifted toward their present positions. But why these eels ended up spending most of their lives in fresh water is another mystery. Rivers are no-go areas for most sea fish, but like bull sharks and rays, eels were able to make this transition. And once inland, there must have been some advantage to make them stay. Perhaps they found better food supplies or more hiding places or fewer predators.

  New Zealand is home to three species of freshwater eel, the largest of which is the longfin eel (Anguilla dieffenbachii). This is said to be the largest freshwater eel in the world, a sliver of information that has been in the well of my memory for many years. And, on reflection, there’s every reason why this should be true. Adrift on the fringes of the shifting continents, New Zealand is ecologically unique, having been beyond the spread of mammals until humans arrived. So huge flightless birds, including the quarter-ton moa (Dinornis robustus), came to dominate the land, and only the supersized Haast’s eagle (Hieraaetus moorei) hunted these—until the Maori arrived. Underwater, the picture is similar, with few native species. So the interloper from the sea has become the top predator, with nothing to hunt it as it slowly grows, waiting for its call back to the sea. But could this flesh-and-blood fish be the creature behind Cook’s report of an eight-foot-long devourer of men?

  There are recent stories that seem to support this. In 1971 eightyear-old Carol Davis was paddling in a stream near the small town of Maheno when an eel grabbed her ankle and started pulling her toward deeper water. Eels can swim backward, so it must have felt like a dog attached to her leg that only let go when the girl’s older sister came to her aid.

  I heard another tale from Brian Coffey who, in the 1970s, was an ecologist working with a dive team doing maintenance on the Arapuni dam. Working with lights in one hundred feet of water, they would often see a huge head looming out of the murk, or part of a snakelike body, but never the whole animal owing to the poor visibility. Although large eels are invariably female, they christened their shadowy companion “Horace” and amused themselves on long saturation dives by occasionally tugging a workmate’s fin or bumping him on the shoulder. One day two divers were decompressing, ten feet down, clipped to the grill over the turbine intake, when one of them saw the eel’s tail against the dam wall ... and whacked it with his hammer. Understandably, the eel bolted, colliding with the other diver, Ian Sutherland, and breaking two of his ribs. The severity of this injury confirmed Horace’s monstrous size—until the next day, when she was found dead on the surface. Her head was indeed very large, but her body, although nearly a foot across at its thickest point, was only four feet long. “She was a fat slug of a fish,” said Brian. “She was probably the only big eel in there.”

  He speculates that she was imprisoned in the lake, unable to follow her migrating instinct. So she stayed there and kept growing. This could be why some eels reach a very large size: old-style dams or steep banks block their way to the sea, allowing no easy exit. However, even for eels that aren’t imprisoned, there is no set size or age at which they migrate. Some stay in fresh water long after their contemporaries have left. I asked Brian if that was the biggest eel the divers saw. He said that in Lake Wanaka, before it was fished commercially, they’d spotted eels with the same body mass as themselves.

  Another diver, Clint Haines, was searching for a friend’s boat propeller one hundred feet down on the bottom of Lake Rotoiti near Nelson on South Island when a “huge” eel swam toward him. Within moments others joined it, one of which grabbed one of his dive fins. Panicking, he dropped his flashlight and kicked for the surface. His wife, who was waiting in a boat above, says the eels pursued him to the surface, and Clint was screaming to get out of the water. He had come up so fast from deep water that he collapsed with the bends. Mr. Haines had seen forty-pound eels caught from the lake and estimated these fish were about eighty pounds.

  For my first look at a New Zealand longfin, I went to the Mangawhitikau cave system near Waitomo, in North Island. Here, in near-total darkness in a river that runs through subterranean tunnels in the limestone, lives an individual known to Te Pare as “the caretaker,” but that is more popularly called Gollum. Normally the only illumination comes from dim constellations of glowworms on the cave roof, so you’d expect a bright flashlight beam on the shallow clear water plus the vibrations that six people dragging film kit make to cause some alarm to anything living there. But the effect was exactly the opposite. A black shape a yard long slid through the shallow water to meet me, clearly in expectation of my offering. The water was so clear, she appeared to be gliding through air. I could easily see the pronounced dome of muscle on top of her head that all large longfin females have, the reason for their vicelike bite and a feature that disappears prior to their final migration, when they stop feeding. I dangled a finger-sized strip of goat meat in front of her, and she appeared to locate it by smell rather than vision before sipping at it and then taking it with a loud slurp. This was a great opportunity to get some underwater footage, but the next time she approached she ignored the meat and went for the camera, biting the lens and chewing its strap. Perhaps she was responding to minute electrical currents and thinking it was some kind of rival or competitor on her patch. Interestingly, there were other eels down there, but none in what appeared to be her territory apart from one that I saw pulling itself tail-first into a cranny between loose rocks a good six inches above the water line. As it did so, I heard echoes of Cook’s words: “He said that they burrow in the ground.” Clearly the big one was not used to upstarts in her patch, so we removed the camera and tried to regain her confidence, and eventually we had her crawling half out of the water onto the base of a smooth low stalagmite. She seemed to be curious about me, as though there was some kind of intelligence there, and I wondered how she experienced her world and what swimming to this place along an underground river had been like.

  After three days in North Island, the crew and I got up at 5 a.m. and caught a flight to Christchurch on the South Island. From eighteen thousand feet, the geology of the land is made clear in a way that it isn’t at ground level. Erosion has sharpened the mountains into serrated ridges, between which the rivers flow, gnawing away at the rock and depositing it on the flat coastal plains. Looking down, I thought of the elvers making their way against current and gravity, intimately penetrating the land like a swarm of parasites.

  But they are a gift to the land. Although their life cyc
le is a mirror image of the salmon’s, which grow to adulthood in the sea and then fertilize the rivers with their dead bodies, eels still bring nutrients from the sea, packed into the bodies of multitudes of elvers. As is the nature of things, most of these will not make it to the top of the food chain. In the past the Maori harvested them, as they were a vital protein source, and they are still fished today. I went to see fishermen on Lake Ellesmere who dig blind channels to trap migrating adults, which can be handled safely because they’ve stopped feeding so they don’t bite. The fishermen’s catch is exported to Europe and Southeast Asia, and although eel numbers are way down on historical levels, New Zealand is about the only place left in the world with a viable eel fishery, thanks to taking conservation measures in good time. All longfins over nine pounds have to be returned. Once they reach the sea, though, their peregrinations are as mysterious as those of the European eel, but biologists think they breed over a thousand miles away, south of Tonga, from where the ocean currents bring the young back home.

  Not far from Lake Ellesmere, in Christchurch, is the National Institute of Water and Atmospheric Research (NIWA) and the laboratory of Don Jellyman, their principal freshwater fish scientist. He showed me recent pictures of the biggest eel he’d seen in a long time: a “feeder” measuring four feet, eleven inches and weighing just under thirty-one pounds that was trapped from a stream running into the lake. In part, the maximum size of any fish species depends on how long they live— and eels are extraordinarily long-lived. I watched as Don dissected out a tiny flake of bone from inside an eel’s head, an otolith, or “ear stone.” These lie in nerve-lined cavities and give the eel information about its orientation and movement. Equally significantly, they grow throughout life, producing clear growth rings, where growth stops each winter, that are visible under a microscope. The oldest eel that Don has aged was 105 years old. He doesn’t dismiss the possibility of them growing to eight feet and a weight of over one hundred pounds.

  This dissection also yielded information about the eel’s diet. Inside its stomach was another, small eel, already well digested. But the surgical gloves on my hands were not worn for reasons of squeamishness. A splash of longfin blood on the lips or eyes can cause inflammation, and only three teaspoons, if it were injected, has enough toxin to kill a person.

  From Christchurch we drove across the southern Alps to Hokitika on the west coast, on the trail of the biggest living freshwater eel known about anywhere in the world. Four years before, so we’d heard, one of the longfin eels in the aquarium here had been netted and measured at over seven feet. This is close enough to the dimensions Cook gave to substantiate that part of his report, and it would potentially look like a devourer of men to anyone in the water. My job was to get in the tank and verify its size, hopefully without confirming its liking for human prey. This would mean netting it again and this time weighing it, which wasn’t done last time.

  The circular tank was some ten feet deep, and my first surprise was the sheer number of eels in it. Instead of one fat individual lying on the bottom, there must have been more than fifty, mostly in and around a large tree root. In the center a stone-clad column housed the filter unit, and a close look revealed portions of eel tail protruding from holes in this where, despite its underlying structure of bolted steel mesh, they had forced entry. Accurately gauging the size of the eels that were visible through the curved, distorting glass was difficult, but they were undoubtedly large and thick bodied. I put the longest ones at five feet, which meant the big one must have been hiding.

  While the crew prepared lights and worked out camera angles, I lay on my back and did some breath-hold exercises, working up to three and a half minutes, followed by one breath-hold of two minutes while walking around. I tried to relax mentally, to push away thoughts of being nipped out of curiosity, of teeth catching in neoprene, of a panicked fish pulling further into cover ... but I knew my pulse would shoot up under water, cutting my time right down to thirty or forty seconds. On top of that, the water was icy. When I lowered myself in, the cold went right through my three-millimeter wetsuit and knocked the breath out of me, making my body immediately demand extra oxygen. I tried to breathe evenly through the snorkel while scoping out the eels from the surface, and then—no point delaying any more—I made the most complete exhalation possible, followed by a deep intake from the diaphragm, and dove down.

  Immediately I felt uncomfortable. Despite my fascination with fish, there is something about eels that disturbs. I think it could be the fear of anything snakelike, which is hard-wired into all of us. The thought occurred to me that I was going into an underwater nest of vipers, but I pushed it aside and tried to look for the big one—or, rather, the big girl, I reminded myself. Somehow the knowledge that these were all females made the situation feel less threatening, although I didn’t pause to question the logic of that. For their part, the eels regarded me with curiosity, turning toward me when I approached but drawing away when I got too close. Three of them, Medusa-like, had their heads and half their bodies protruding from the root mass. With subsequent dives I gained confidence, but the cold was working through me. From this viewpoint I could see what wasn’t visible from the outside: that several eels were hidden between the boulders of the perimeter wall. One of these looked bigger than the rest, with its head looking out from one hole and its tail sticking out of another. I wondered how territorial these fish were, whether the bigger individuals muscled the others out of the best, most secure lies. This could explain why I hadn’t seen the big one. And if a seven-foot eel can stay hidden in a small tank of clear water, how would you ever find such a fish in the wild?

  After running to the shower, where I gushed hot water inside my wetsuit, I asked one of the aquarium workers when the big eel had last been seen. Not since it had been netted, he said. It had some kind of growth on its head, so they hadn’t put it back. I had been hunting a phantom. As for its size, he directed me to one of the other staff, who couldn’t remember.

  “But it was significantly bigger than these ones,” I prompted.

  “Not really,” she replied.

  So where had the reported seven-footer come from? Nobody knew. I’d found a real case of spontaneous generation.

  But we still had the net and my 230-pound scales, so we decided to go after the biggest one we could see. This turned out to be “Number 7,” so called because of a pronounced downward kink in her neck, like an arthritic grandmother. Seeing that she was lying in an open area of the bottom, I dove down and scooped her head into the meshes, but her broad tail wouldn’t fold inside, so I supported it in the crook of my arm as I surfaced, hoping she wouldn’t wake up to what was happening and reverse out. Hands above me took the net’s handle, and there she was, lying quietly on the damp mat that we’d laid out—before grabbing the edge of our wooden platform with her tail and pulling herself back in the water. But by then we had the data we needed: a length of exactly five feet, and a girth of eighteen inches, giving a weight of thirty-five pounds—an impressive fish, but well short of the size we were hoping for.

  Although the seven-footer had vanished on our approach, we then heard stories of “huge eels” in some dredge ponds nearby from the days of the gold rush. But there was no time to check these out because we had a flight to catch. At the check-in desk they told us not to hand back our hire vehicles just yet. Because of low cloud, there was some doubt whether the incoming twenty-seater would be able to land. At length, we took off through squally clouds, climbing steeply to clear the Alps. But the worst lurching and rattling came on the other side when we flew between windswept clumps of cloud with the flat coastal plain beneath us. One of our crew heard the passenger behind him praying.

  The next stop was Invercargill at South Island’s southern tip, where I met Vic Thompson, the manager of an eel processing plant that sends eels on aerial journeys as far as Billingsgate market in London. The biggest eel he has seen out of the water was a fifty-two-pounder, squeezed into one of his fyk
e nets when he was a commercial fisherman. But he’s seen two shapes in the water that were bigger than that: one that he first thought was a log that took a bait his uncle fished and nearly pulled him in the water, and another close to the length of his ten-foot boat. He’s also seen eels attacking sheep, overpowering them in a stream where the banks were too slippery for the animals to escape. The eels burrowed into one sheep’s anus, ripped out the intestines, and ate the internal organs.

  At Vic’s suggestion, we met at a creek near his plant just before dusk. Finally, I was getting my rods out—a whole week after arrival. I set up a very simple rig: a forty-pound main line with a running lead on a weak link that was stopped by a rubber bead and a barrel swivel, with the hook attached to eighteen inches of fifty-pound wire. I opted to use a circle hook because these normally catch in the edge of the mouth, with a crushed-down barb for easier unhooking. I nicked this in a small mackerel strip, keeping the point clear, and swung it toward some trailing branches on the opposite bank. With Vic chumming the pool’s inlet with abalone guts, the first run came very quickly. I let it go for a few seconds, but as soon as I closed the reel and tightened, the fish fell off. My lack of cursing puzzled the crew, but I assured them I knew what I was doing. A bigger fish would take the bait properly, whereas a small one would just hang onto it, so this method would select the bigger fish and avoid the messy business of unhooking small ones. For once, the practice bore out the theory, with a handful of smaller eels dropping off and a couple of bigger ones being slid up the bank, although at less than three pounds, these were not as big as Vic had been expecting.

  Vic also taught me how to “bob,” a traditional way of fishing without a hook that he had used as a commercial fisherman. At first I wasn’t convinced, considering it only marginally more likely to succeed than the lamb intestine method Claudius Aelianus described in the second century. (You put a reed tube in one end and dangle the other end in the water. When an eel grabs it, the fisherman blows “with all his might” and inflates the eel.) To make a bob, you wrap a strip of fish or meat in wool. It works because the eel’s tiny teeth get tangled in this—and because its predatory instinct makes it reluctant to release its meal. Normally the bob is fished on a piece of strong cord that is attached to a stiff pole. When you feel the eel take, you allow it a few moments before hauling it unceremoniously onto the bank. I also cast out a bob using a rod and reel, and I found that, if I pumped in the line in a smooth and businesslike way, I could land a good proportion of the eels that took.