Dawson fish trap produces unexpected catch
Arctic lamprey have an image problem. They're fish, but they don't look like fish.
In fact, they're so unlike our usual image of a fish that we rarely notice them.
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Adult arctic lamprey like this specimen have been turning up in a fish trap near Dawson.
(photo: Jake Duncan)
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This year, Jake Duncan can't help but notice them. The fisheries researcher and his partner, R.J. Nagano, have been catching adult arctic lamprey in a fish trap near Dawson since the end of May.
The rotary auger trap is part of a program, funded through the Yukon River Panel's Restoration and Enhancement Fund, to track the migration patterns of juvenile salmon heading down the Yukon River.
This year's haul of adult lamprey is a first, says Duncan.
"We have seen lamprey before -- just not adult lamprey. The juvenile lamprey we have sampled in the past have been roughly 8 to 10 centimetres in length and look much like earthworms."
Adult arctic lamprey are a different thing altogether, he says. The individuals showing up in Duncan's trap are about 30 centimetres long, and their mouths are round suckers lined with sharp teeth.
"They look like wormy eels," says Duncan, who admits to finding them "really quite gross."
Al von Finster, a biologist with the Department of Fisheries and Oceans, had heard of adult lamprey turning up in Mica Creek near Pelly Crossing 20 or 30 years ago. There are also local and traditional knowledge accounts of them in Old Crow, and consultants have found juvenile lamprey in the Nordenskiold River, he adds.
But he'd never actually seen an adult arctic lamprey in the Yukon before this year, despite many years' studying fish and habitat in the territory.
"If we hadn't had the rotary trap in the river, we'd never have known this was happening," he says.
Steve Gotch, also a biologist with the Whitehorse office of Fisheries and Oceans, says the lamprey have been documented in the Alaskan portion of the Yukon River for at least the century, but relatively little is known about the distribution of this species in the Yukon portion of their range. Most people simply don't encounter them, he says.
For one thing, lamprey spend a large portion of their lives well out of human sight.
During the first part of their two-part life cycle, the juvenile lamprey, or ammocoetes, burrow into the sand or mud bed of the stream where they hatched. They stay there, blind and toothless, for up to seven years, feeding on microscopic plankton or algae particles which they filter out of the water.
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Researcher Mike Bradford tidies the mooring line on the rotary auger fish trap near Dawson. Unusual numbers of arctic lamprey have been caught in the trap this year.
(photo: Jake Duncan)
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Then they undergo a physical transformation, developing eyes, a sucker-like mouth, and short horny teeth around the mouth and on the tongue. While the transformation is taking place, they emerge from the streambed and migrate downriver to the sea.
"Once the transformed lamprey reach the ocean, they become parasitic adults, actively seeking out fish on which to feed," says Gotch.
The adult lamprey use their oral suckers to attach themselves to fish like salmon or even sharks. With their tooth-covered tongues, they rasp through the scales and skin of the host and begin feeding on its blood and body fluids. Usually after a few days, the lamprey detaches itself and swims off in search of a new host.
No one is sure, says Gotch, exactly how long adult lamprey remain in the ocean, although it's most likely anywhere from 8 to 32 months. When they reach sexual maturity, they migrate back to the stream where they were hatched, perhaps hundreds of kilometres away.
Back in their home stream, sometime from late May to early July, the lamprey excavate a nest in the gravel of the streambed.
"The male lamprey will attach himself to the head region of the female, by use of his sucker, and wrap his body completely around her," explains Gotch. "The pair will vibrate rapidly, releasing both eggs and sperm simultaneously."
Females usually lay 10,000 to 30,000 tiny white eggs, which fall to the bottom of the nest and lie there unburied. Anywhere from 10 days to several weeks later, the eggs hatch and the ammocoetes burrow into the streambed to begin the cycle again.
Like Pacific salmon, the lamprey adults die after spawning. Von Finster speculates that the lamprey turning up in the Dawson rotary trap have been swept down from upstream spawning grounds.
Gotch says the unusual number of adults reported this year is likely a combination of natural fluctuation in the spawning population and the fact that they are in a place where someone is looking for fish -- in this case, Jake Duncan and the rotary auger trap.
- For more information about arctic lamprey and other Yukon fish, contact the Department of Fisheries and Oceans at (867) 393-6722.
