Local biologists help bring walleye back to Lake Wabamun
Friday, Jul 11, 2014 06:00 am
It’s the morning of June 4 at Lake Wabamun. Alberta fisheries technician Don Hildebrandt is taking his foster kids home. All 5.2 million of them.
“Swim free! Swim free!” he says, as he gently tips a bucket of what looks like foggy water into the lake.
Only upon closer examination is it apparent that the bucket is actually full of thousands of tiny, living fish, each the size of an eyelash, their eyes smaller than a pencil tip.
For these babies, this is the last step in a four-week journey, an ongoing effort by Alberta Fish and Wildlife to bring walleye back to Lake Wabamun.
Back from the brink
These particular baby fish (or fry) got their start as eggs collected from Lac Ste. Anne on May 11.
On that day, St. Albert resident and provincial fisheries biologist Owen Watkins rockets out towards the middle of the lake to collect some adult walleye for spawning.
“Perfect day for this,” he notes – not like yesterday, when the winds and ice flow were wrecking their traps.
Walleye are large, silvery fish with big spines on their dorsal fins, Watkins says. They possess giant, marble-like eyes that give them excellent low-light vision, letting them hunt and eat other fish. Unlike their virtually identical cousins, the saugers, walleye have a white spot on the lower lobe of their tails.
Walleye are probably the prime eating fish in Alberta and a frequent target for anglers, Hildebrandt says – so much so that their populations have collapsed in many regions.
People used to haul them out of Lake Wabamun by the trainload in the 1940s, notes Stephen Spencer, another fisheries biologist and St. Albert resident working with Hildebrandt and Watkins. That drove the species to extinction in the lake – it’s been effectively walleye-free for almost a century.
The loss of the walleye not only meant less fish for fishermen, but ecological chaos in the lake.
Walleye were an apex predator in Lake Wabamun, Spencer explains. Without them around, populations of prey species such as whitefish have been on a rollercoaster for many years now.
If the province can restore walleye to this lake, it could not only restore its ecological balance, but potentially reopen it to sport fishing.
“People are quite excited about this project.”
This is actually the province’s second attempt to restock the lake, Spencer noted. The last one in the 1980s failed because warm water from a TransAlta power plant tricked the walleye into spawning too early, meaning that their fry didn’t have any food to eat.
The province launched this latest effort after TransAlta closed its plant on the lake in 2010.
Watkins pulls the boat up to a cage set atop a shoal in the middle of Lac Ste. Anne.
“The walleye come up here to spawn,” he explains, as he hauls in the net.
A fence along the shoal directs them into the funnel-shaped cage, trapping them by the hundreds.
There’s not much romance when it comes to walleye mating, Watkins explains. The fish gather over a gravelly area like this shoal, drop their eggs and sperm-laden, milky milt, and depart.
Once he’s emptied the trapped fish into an oxygenated cooler, Watkins zooms back to shore and sorts them by sex – a simple matter of stroking their bottoms and seeing what comes out.
“Some of them (the females) are so ready that you pull them up and they just start dropping eggs.”
The fish then head over to retired fisheries biologist Daryl Watters in a darkened tent called a fornicatorium. Watters is an old hand at fish breeding, having taken part in fish-stocking projects for decades.
“I take a lot of pride in handling and spawning fish quickly and with minimized stress on the fish,” he says.
Watters starts by grabbing a female walleye and using his thumb to push the eggs out of her ovaries, sending a stream of roughly 40,000 golden eggs, each the size of a pen tip, into a stainless steel bowl full of water. (The eggs are light-sensitive, so he keeps the tent dark.)
He then does the same with a male to add milt to the mix. Both fish then go back into the lake.
He moves with frantic energy.
“As soon as the egg hits the water, there’s a pore (in it) that opens called a micropyle and it stays open for about two minutes,” he explains.
If a sperm doesn’t get through that hole in that time, the egg won’t be fertilized.
Watters mixes the eggs and milt using a goose feather to avoid damaging the eggs. After a five-minute wait, he adds some tannic acid to keep the eggs from sticking to each other, washes them with water, and pours everything into a large cylinder called an up-weller that keeps them in constant circulation.
“These are eggs we took yesterday,” he says, describing the churning yellow goo in it.
“There’s probably close to a million eggs.”
In the wild, just five per cent of these eggs would get fertilized, Watters says. Under these controlled conditions, he’s able to fertilize 95 per cent.
The fertilized eggs are trucked to the Cold Lake Fish Hatchery for finishing.
The hatchery is temperature-controlled and in operation 24/7, said Craig Copeland, provincial fish culture manager and mayor of Cold Lake. It’s the only walleye hatchery in Alberta, and it can raise up to 100 million fry at once.
Crews transfer the eggs from the up-wellers into racks of smaller, more manageable jars. Each jar holds about 300,000 eggs.
The eggs are kept under constant circulation for about 25 days, with the temperature in each jar slowly raised from eight to 16 C over that period. Crews siphon white, unfertilized eggs off the top of the jars and add disinfectant to prevent fungal growth.
The fish grow swiftly during this time, forming their bodies and dot-like eyes before they all emerge at once.
“Over a day or so, about 300,000 fish will hatch out of a jar like popcorn,” Copeland says. Each carries with it a yolk sack that will serve as its food for up to a week.
Since the fish may eat each other if kept too close together, the tops of the jars flow out into a large tank to give the fry some personal space.
Once hatched, the newborn fry get shipped down to Hildebrandt for release into Lake Wabamun.
Those fry start off about four millimetres long and grow a millimetre a day, Copeland says. They’ll be about 12 centimetres long by October, having moved on from plankton to other, bigger prey.
Fish for the future
About 5.2 million (76.5 per cent) of the 6.8 million eggs collected from Lac Ste. Anne this year were successfully raised into fry, Copeland says. In the wild, maybe 0.1 per cent of those eggs would have made it.
One to five per cent of those eggs will reach adulthood, Hildebrandt says. It will be at least five years before they’re old enough to reproduce.
These fish are from the same watershed as Lake Wabamun and should be well adapted for its conditions, Spencer says.
Some of the adult walleye the province put into Lake Wabamun a few years ago already appear to be spawning in the lake, he notes – a good sign, but it will be least five years before researchers know if the lake’s population is sustainable.
Like his fellow fisheries operatives, Watters takes being a nursemaid to several million walleye as just another part of the job.
“It’s one of those work-hard-and-feel-like-you’ve-accomplished-something-at-the-end-of-the-day type projects.”