Alien fish species Threaten the Ecosystems they Invade

By Robert Koopmans

Some anglers may see them as worthy game species but according to biologists, foreign fish dumped in waters where they don’t belong spell disaster.

There are at least four lakes in the Kamloops region now infested with yellow perch, a spiny-ray fish imported from eastern Canada. It’s tasty and easily caught, something that makes it a favourite with fishermen in its native environments.

But in the absence of a natural predator like pike, walleye or bass, perch reproduce quickly — too quickly. It doesn’t take long for their numbers to grow to the point they dominate a lake. After that, it’s only a matter of time before resident species of trout are pushed out.

And yellow perch are but one of a number of alien invaders that have biologists worried about the future of Interior lakes.

Brian Chan, a senior fisheries biologist in Kamloops, is dreading the day someone calls him with reports of largemouth bass in a local lake.

“I’m waiting for it,” he said. “I hope I never see it, but we’ll see it. Within 10 years, we’ll see it.”

Transplanting species of fish from their native lakes or rivers to new bodies of water has often been standard practice for the fishing community.

In decades past, fish managers even aided the introductions of exotic species to B.C.’s lakes and streams. Brook trout, for example, are native to eastern Canada. They are now a regular in many provincial lakes and are still stocked, although only sterile brook trout are released today.

Around the turn of the century, brown trout were also introduced to parts of B.C. and are still found in some watersheds. And most of the landlocked lakes of the Interior that currently hold rainbow trout were stocked, having never had trout in them before.

But Chan noted rainbow trout are native to B.C. Although the many prime fishing lakes of the area were stocked, the fish were taken from extremely similar lakes close in nature, size and location.

Of course, native fish put in places they don’t belong cause problems too. The red-sided shiner, a B.C. native, is perhaps the biggest threat to trout populations in the Interior.

The small minnow is a prolific breeder, Chan said. When introduced to new lakes where the trout don’t prey on fish (the majority of Interior lakes), shiner numbers quickly explode. The shiners eat the same food as trout, depleting the food base. Eventually, the trout will lose the battle for available resources and disappear.

“These minnows and other spiny-ray fish are much higher evolved (than trout) and are more adaptive. They broadcast their eggs across the bottom; they don’t need streams to spawn in. An average perch might have 15,000 eggs. A 10-inch trout might have 110 eggs.”

Most times, anglers used to fishing eastern waters for pike, walleye and bass are responsible for the illegal introduction of shiners. They catch the minnows in Lake A, then use the live fish as bait in Lake B. At the end of the day, they often throw their leftover bait overboard and a new lake is infested.

Most of the guilty anglers don’t realize the small-lake rainbow trout are interested only in insects and won’t touch the shiners anyway, Chan said.

“They don’t understand the vast majority of natural (trout) stocks are insectivores,” he said.

Suckers and chub are moved from lake to lake in much the same way, Chan said. It’s illegal to use live fish as bait in B.C.

The other source of illegal introductions in B.C. are anglers looking to stock a lake with a new species of game fish — perch, bass, sunfish or crappies , for example.

Once again, many of these stockings are done by eastern anglers new to B.C., many who miss the fishing from back home and want to bring a little of it closer to where they now live.

So they catch a few fish from a lake with a resident population of the species they like and dump them in a new lake. As few as a dozen introduced fish can start a new population. It takes on average three to five years for a species to show in sizable numbers once illegally introduced.

“We get lots of phone calls from visiting angler or newly arrived anglers that don’t understand why we won’t put pike and walleye into the lakes,” Chan said.

Yellow perch are now in Pinaus, Skmana, Nellies and Skimikin lakes in the Shuswap. Chan said they could be in more. Two of the lakes are connected to Shuswap Lake, meaning it’s inevitable the perch will make their way to the bigger lake eventually.

There, they will likely take up residence in the places favoured by salmon and trout fry and drive the smaller salmonids out.

At Pinaus Lake, fisheries managers are trying to introduce trout that prey on other fish, but it’s not known whether the two species will strike a predator-prey balance.

The future at Pinaus Lake doesn’t look bright, he said. The perch numbers are expected to increase to a point where trout predation won’t be effective.

“The perch populations will peak and then they will collapse. What you’re going to be left with is a bunch of perch this big,” Chan said holding up his fingers about six centimetres apart.

“You may have 10 or 12-inch perch right now, but that won’t last.”

How long it will take for the crash isn’t known. Pinaus Lake is big and cold and deep and that may slow the perch’s advance. A small, warm, shallow lake like Six Mile Lake outside Kamloops, would be overrun within five years, Chan said.

“It’s getting too close to home with these perch,” he said. “It’s not good news. They are not native here — perch are no where near natural to British Columbia. They are extremely competitive.”

Chan concedes fisheries managers have a “salmonid mentality” in B.C., primarily concerned with maintaining trout and salmon populations.

But those species are the most prevalent native fish and a sport fishery with a worldwide reputation has been built around them.

“We don’t want to lose that” Chan said.

In a perfect world, it might be nice to take a lake and fill it with bass and perch for anglers who like to fish for those species, but Chan said people would never be content with that. Allowing a bass and perch lake in the Interior would only create a source for more illegal introductions.

“People would move them,” he said. “It’s almost impossible to stop people from doing it, people would move them. We can’t take the risk. Those fish would move, they always do.”

Solutions to exotic problems not easy to find.  In decades past, biologists had little difficulty dealing with lakes infested with undesirable fish species — they got out the poison.

Lakes were routinely “treated” with a collection of highly toxic chemicals that wiped out virtually all life. After that, desired fish species were introduced into the system.

Not so today, said Kamloops senior fisheries biologist Brian Chan.“We don’t do that anymore, we are out of that game,” he said.

Up until the 1960s, Toxifine was the poison of choice. It was nasty stuff said Chan, a PCB-based poison and a proven carcinogen.   After it was banned, biologists turned to Rotenone, an organic poison derived from a jungle root. It too was deadly effective, capable of wiping out all life in a lake.

“It killed all sorts of aquatic invertebrates and vertebrates. It was hard on amphibians and reptiles. From salamanders to shrimp and mayflies to zooplankton.’’

Slowly, the Ministry turned away from poisoning once the environmental impact of such practices became apparent.

Most of the prime fishing lakes in the area — the entire Roche Lake chain, Dragon Lake, Sheridan Lake, Heffley Lake and White Lake to name a few — were all poisoned and restocked at some point, Chan said.

 

And some lakes were poisoned more than once. Courtenay Lake near Merritt was treated for a shiner infestation. It remained shiner free for several years, but the pesky minnows reappeared. The lake was poisoned once more. Again it remained shiner free for years, but the small foreigner is once again in its waters.

This time, no poisons will be used to extirpate the shiners from the lake, Chan said.

Deep Lake in Westsyde was the last local lake killed off by poison, Chan said. It was treated in the early 1980s after someone released their pet goldfish into the lake.

The golden cousins of the carp took to their new environment and grew to staggering size. There was concern the goldfish would spread to other lakes in the Lac Du Bois area.

The lack of a poisoning strategy leaves today’s fish managers with few options to combat illegal introductions of foreign fish.

The favoured technique is to stock Blackwater rainbow trout into lakes with spiny-ray infestations. Blackwaters feed on other fish and it’s hoped they will keep the aliens in check. It’s not known how successful the strategy will be.

In some aerated lakes, biologists can try to induce a winter kill by leaving the aerators off through the winter months, starving the lake of oxygen. Of course, it’s been proven to be extremely difficult to induce a winterkill on demand, Chan said.

Once a lake is infested with a non-native species — particularly perch — Chan said catch limits are imposed. Currently, a person can’t catch and keep more than 20 yellow perch a day.

While it seems odd to restrict the catch of fish the Ministry doesn’t want, Chan said there is valid reason. If people get to like catching 100 to 150 perch a day —something possible on a full perch lake — they might decide to move perch to a lake closer to their home, so they don’t have to travel as far.

In the end, angler education is the only tool that might save future Interior trout lakes from death by foreign invasion.

Chan said there are numerous documents outlining the problem available to anglers, including information in the provincial fishing regulations. As well, a video outlining the problem is in the works.

When people call asking why B.C. lakes can’t have bass, walleye, pike and perch, Chan said he tells them about the destructive impact.

“I tell them what we got here, why we have it here and the problems associated with introducing a non-native species,” he said. “I tell them we don’t want them here.”