Lampreys have done without bones—even jaws—for 360 million years, making do instead with a mouthful of rasps designed for shredding. But those teeth are no match for a new and invisible enemy. Are pesticides killing the lampreys? Scientists are scrambling to find out.
Christopher Swain has swum thousands of kilometres, through some of America’s filthiest water. He’s been run over by boats, swept down rapids and covered in toxic waste, but the crusading marathon swimmer’s worst fear came at him from the turbid murk of Lake Champlain, Vermont. In the middle of a 200-kilometre fundraiser, he felt something “like when your phone rings in your pocket, and it’s on vibrate”.
He reached down and felt something bound to his thigh—something thicker than his wrist. “I tried to grab it, but it slimed right out of my hand,” he told reporters. Peering through the brown waters, he saw a metre-long sea lamprey locked onto his wetsuit. Next time, he managed to tear it free, but it promptly latched onto him again. “They want your blood and nutrients,” he recounted. With a final effort, he wrenched the thing off and flung it as far as he could.
Over the years of his water pollution campaign, Swain has been attacked by sea lampreys dozens of times, which is unsurprising: in the bigger lakes of the American north, they’re a plague. Each year, the US and Canadian Governments spend between US$10 million and US$15 million on sea lamprey control, after the bloodsuckers took advantage of newly opened shipping canals in 1835 to infest the Great Lakes. There, they stand accused of the extinction of at least three species of freshwater fish and the persecution of prized sports fish salmon, trout, walleye—and the threatened lake sturgeon. By the turn of last century, lampreys had already purged Lake Champlain of its last salmon and lake trout.
Sport fishers have goaded authorities into massive poisoning offensives, and while catches have improved, the lampreys will endure, costing the Champlain Basin alone an estimated US$29 million a year in lost sport-fishing and tourism revenue.
To look at it another way, that’s impressive witness to the abiding power of one of the most primitive vertebrates on Earth the most base of the backboned. Look at a lamprey and you’re peering back at least 360 million years, into the farthest dim mists of the Devonian. (They may be older still, because lampreys were made then, as they still are today, mostly from cartilage, which fossilises poorly. Maybe we just haven’t found their remains.)
Lampreys once swam upstream past herds of drinking dinosaurs, and have prevailed over at least four mass extinctions.
An X-ray of a lamprey is like some evolutionary Shroud of Turin: the tracery of a relic. Of more than 45,000 vertebrate species, only they and their relatives, the hagfish, never bothered growing jaws. Biologists have made a case study of the lamprey’s brain, because they believe it still most closely resembles that of our primal vertebrate ancestors. Lampreys have also taught us about fundamental vertebrate motor control—and their immune system, evolved entirely separately from that of higher vertebrates, is a relic physiology.
So the lampreys’ conquest of the Great Lakes is a bit like a mob of Neanderthals taking over Wall Street. The oldest lamprey fossil—laid down when the earliest vertebrates first tottered onto land—looks much the same as the one that accosted Swain. A lot like an eel: sinuous, slimy and scaleless. But their fins don’t come in pairs, as in most other fish. In fact, asymmetry is something of a trait: lampreys bear a single nostril on the top of their head, and their trademark below it—a circular, murderous-looking maw of hooks, which they use to fasten to prey. At the centre, a structure more appalling still: a tough, mechanical rasp of a tongue that scrapes away scales and tissue to get to the blood beneath.
Like mosquitoes, lampreys secrete an anticoagulant that keeps blood flowing. One might stay attached for minutes, or days. At Lake Champlain, where fish are accosted regularly by lampreys, there’s an even chance the victims will die: mortality swings between 40 and 60 per cent. Survivors might succumb later to infections from the wound, and many are found with scars from multiple attacks.
There are 41 recognised lamprey species around the world—some marine, some freshwater, but most a bit of both. They’re found in temperate waters practically everywhere, and not all are parasitic. Some largely freshwater varieties filter-feed as larvae—called ammocoetes—which spend up to seven years burrowed into the sediment of their natal river, feeding on detritus they trap on sticky strands of mucus. Then they morph over months into adults, which migrate either upstream to a lake or downstream to the sea, depending on their lifestyle.
New Zealand’s native species is Geotria australis, the pouched lamprey, named for a baggy pouch growing beneath the eyes of sexually maturing males. After four years as an ammocoete, it develops into a juvenile and swims down to the sea, where it spends three or four years harassing other fish—even whales—before returning in autumn and winter to breed in fresh water. These life stages are so physically dissimilar that 19th-century biologists described them as separate species. Once it enters a rivermouth, G. australis gives up its bloodsucking ways and will not eat again.
By now, returning adults might be 75 centimetres long. Sleek and silvery-blue at first, they use their mouthparts to climb logjams and waterfalls. If they can’t climb over the barrier, they’ll go ashore and wriggle around it—some have conquered a 14-metre-high dam on the Arnold River on the West Coast this way. They move at night, preferring a feeble moon or the cover of cloud and a stream swollen with recent rain. But it’s a debilitating quest, and their livery soon fades to a dull brown. On the Whanganui, they routinely migrate 240 kilometres to Taumarunui reaches, where they’ll linger for up to 16 months before spawning. Then they’ll die.
And that was about as much as we knew about New Zealand lampreys until recently. The species has also been recorded in southern Australia, Chile and Argentina, and while biologists believe it probably ranges around much of the New Zealand coast (it’s also been reported on Stewart and Chatham Islands), lampreys are rarely seen, perhaps because they’re thought to burrow into stream beds or hide under logs. We know almost nothing of their life at sea, except that they make lengthy journeys: adult G. australis have been found attached to fish in subantarctic latitudes.
Their breeding habits, too, were a total mystery until one day last October, when NIWA freshwater ecologist Cindy Baker turned over a boulder and saw something familiar writhing in the Okuti River on Banks Peninsula. In a bid to track them to their spawning grounds, she had fitted electronic beacons to some lampreys 12 months earlier. After months of tracking, she and Michigan State University colleague Tyler Buchinger found the nests of three pairs: the first ever located in the southern hemisphere.
Until then, everyone had assumed wrongly, it turned out—that southern lampreys laid their eggs in streambed gravel, like their northern hemisphere relatives, which is why Baker had never thought to go look under a rock. But then, our lampreys do a lot of things differently.
“What’s really neat about our fish,” says Baker, a NIWA aquatic ecologist, “is that they can sit in fresh water for more than a year without feeding, and just use their muscle tissue to grow gonads. They end up with these morphological changes that we’re only now beginning to understand.” Overseas, male sea lampreys, for instance, develop a ‘rope’ of fatty tissue down their back, once believed to be a visual barometer of physical fitness to females. But in New Zealand, says Baker, “we found that it’s our female that produces that rope”.
Then there’s that odd pouch: “We still don’t know what the purpose of that is.” One thing’s certain, she says—it’s not a brood pouch for harbouring youngsters. “Maybe he fills it with gravel to clear a nest site.” (The pouches of some northern hemisphere species were found to be brimming with lipids—nature’s energy-storing molecules that include waxes, fats and vitamins—prompting a hypothesis that they might be a sort of storehouse to sustain the lampreys during their long pre-spawning fast. In New Zealand, lipids make up around 20 per cent of the bodyweight of a returning adult.)
Ordinarily, says Baker, males arrive first at a spawning stream, where they choose and build a nest site. Then they pump pheromones into the water to attract suitors.
Baker, who’s made something of a speciality out of fish pheromones, says that “normally, fish emit compounds in nanograms per hour: these guys emit in milligrams, truly enormous amounts. That’s unheard of.”
To power such a potent broadcast, a male’s liver engorges, says Baker, “but we’ve now found that both males and females here have enlarged livers, so we’re wondering if maybe they’re both producing pheromones.”
Chemical signals direct many of a lamprey’s life choices: none more critical than where it decides to breed. Unlikesalmon, lampreys don’t slavishly return to their natal stream. Instead, they sift the brackish waters of rivermouths for bile acids, a powerful pheromone emitted by ammocoetes upstream. The stronger the signal, the more ammocoetes in the stream, and the better the breeding site is deemed to be.
This single strategy could yet determine the fate of New Zealand’s lampreys, because something is going wrong for them. Down the centuries, they’ve filled the kai baskets of generations of Maori around the country. Utu piharau—weirs—were laid across a river, angled so as to direct the lampreys to a narrow vent at the far side, where the current swept them into a hinaki (eel pot). There are stories of throngs of migrating lampreys a mile long, of bulging hinaki and long afternoons drying the creatures known as kanakana in the South Island and piharau in the North—on the riverbanks.
In 1918, T.W. Downes penned an account of a night’s fishing on the Waitara River: “…for a single night’s netting during a fresh in June, three sacks were filled—probably between two and three thousand.”
But lampreys have since vanished from many North Island reaches, and catches along the Whanganui are now a pittance. Only Southland remains a stronghold, but even there, says local ecologist Jane Kitson, “people have certainly noticed a change in the numbers coming in”. She’s heard tales of lampreys so profuse they blocked field drains: “We don’t see that any more.” Kanakana were once the bane of whitebaiters, she says, but locals along the Clutha Mouth told her they haven’t seen one in 20 years. Nevertheless, “kanakana haven’t been lost from people’s memories—they still play a huge role down here, among those who distribute them round the kaumatua and elders.”
In Southland, lampreys are harvested soon after they arrive from the sea, because once they begin to develop gonads, they’re not great eating. People mostly pluck climbing lampreys from natural barriers, such as Mataura Falls, or fossick for them during the day among rocks and crevices. Harvesting sites are closely guarded and monitored, which makes the whanau of Southland key witnesses to the mystery of what ails the kanakana.
In October 2011, fishers along the Mataura River found lampreys dead and dying, their silver sides marred by angry red lesions. Ministry for Primary Industries post-mortems found their muscles and organs bleeding. Preliminary tests turned up the bacterium Aeromonas salmonicida, a freshwater pathogen common around the world, but previously unknown in New Zealand. However, before pathologists could pin the deaths on anything, the migration ended and they ran out of samples.
Testing continued in 2012 and 2013 and scientists ruled out the influence of the any known pathogen. Scientists are now investigating accumulated anticoagulants from the common rat poison brodifacoum that have been found in river and estaurine sediments—some two-thirds of sick Waikawa lampreys tested positive for bromadiolone, another type of anticoagulant, which has also been found at trace levels in the Waikawa estuary. “It could be a multiple, cumulative effect,” she muses.
Certainly, our love affair with hydro power has evicted lampreys from many of their ancestral spawning grounds. They cannot scale the likes of the Monowai Dam—the Waiau was a celebrated kanakana river before the advent of hydro.
Lampreys still sometimes mass at the foot of their vast concrete nemeses.
Murihiku whanau are doing their own monitoring and counts, keeping a watching brief on an ailing taonga. “We need to know why they’ve declined. Is it a water quality problem? There’s a lot of drain clearance going on in Southland these days, and the ammocoetes are very vulnerable as they spend that part of their life in the sediment. Digger drivers tell us they come up clinging to the bucket. These are all small cuts that together could add up to a huge impact,” says Kitson.
Meanwhile, Cindy Baker is hatching a plan to fox lampreys into re-colonising streams long abandoned. Control work in the Great Lakes has exploited those pheromones the lampreys follow—but Baker means to use them to lead the creatures to deliverance, not destruction. By synthesising those bile acids emitted by the ammocoetes, and beaming them from river mouths, she hopes the lampreys can be duped into reclaiming some of their ancestral range. “We’re part-way through identifying the pheromone cue, and they’re attracted to one of the compounds we’ve tested,” she says. Unfortunately, the lampreys died before she could isolate the successful pheromone.
For Kitson, re-seeding “could be part of the answer, but it doesn’t address the cause of the problem: what can we do to stop the decline?” Mahinga kai—freshwater food species—she says, “is the cornerstone of who we are. It would leave a gaping hole if we were to lose them. It would be a very, very sad thing.”
Many might find them repellent, but not Kitson: “I’ve never seen anything as beautiful, yet so strange… it’s almost as if they’re not from this world.” In one sense, that’s true: they come from a different age of life on Earth. Whether they can survive in this one is less certain.