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Hardship for people, not wildlife

Fish, aquatic invertebrates may benefit from high water

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Widespread flooding in southern Manitoba this spring may have a beneficial effect on some aspects of the natural environment, even as it displaces people and disrupts commerce.

The 2011 flood should be a boon to fish and aquatic invertebrates that rely on major deluges to maintain their populations. All major floods carry fish, crayfish and other species from large rivers to smaller bodies of water, said Bill Watkins, biodiversity conservation zoologist with Manitoba Conservation's wildlife branch.

"For the most part, this is a good thing. When you think of fish trapped in a small pond or an oxbow lake, over the years they inbreed and that begins to affect their biodiversity," Watkins said in an interview.

One species that's utterly dependent on floods is a common but rarely seen crustacean called the calico crayfish. Unlike the better-known northern crayfish, which lives in the clear waters of the Canadian Shield, the calico crayfish thrives in muddier bodies of water -- including streams and Prairie potholes that sometimes dry out completely, Watkins said.

The calico crayfish survives by performing two unusual feats -- it can burrow down into the mud to wait out dry conditions or can actually get up and walk to a more favourable pond or stream.

"The calico has the unique ability to head out cross-country. It just can't go very far," Watkins said. "I've also dug up burrows that are more than a metre deep."

What the calico can't do is withstand any significant current. When a flood comes, it simply gets carried away, which may in fact be to its evolutionary advantage.

Floods may also boost populations of walleye and sauger in Lake Winnipeg and Lake Manitoba by sweeping more young fish -- as well as the insect larvae they eat -- into large lakes, Fisheries and Oceans Canada maintains.

A major flood has little effect on animals that live above water. Large animals such as deer or coyotes simply move to higher ground to get away from rising water, Watkins said.

Rodents such as mice, voles and ground squirrels may be killed off in large numbers, but their fast rate of reproduction allows their populations to quickly bounce back, he added.

But even mice have the ability to climb trees or find higher ground.

"A colleague of mine in Saskatchewan found an island of dry land that was teeming with mice during a major flood," Watkins said.

Birds largely are not affected by major floods, as most species that nest on the ground have yet to lay eggs, he added. Canada geese are nesting now, but since the size of the flood is near its peak, flood waters do not threaten their nests.

Most trees and shrubs located alongside rivers will also survive the flood, as almost every species native to southern Manitoba is adapted to flooding, Watkins said.

"All the areas that flood frequently have flood-tolerant species," he said.

But there is one caveat: The frequency of floods appears to be increasing.

Environmental scientists say they do not know the long-term effects of more frequent floods on the Prairie ecosystem. Some freshwater scientists believe it's possible major floods sweep more fertilizers and pesticides into Lake Winnipeg.

bartley.kives@freepress.mb.ca

Don't worry

about Bambi

 

How animals endure the flood.

Deer, coyotes and other large mammals: Simply move to higher ground.

Rodents and other small mammals: Drown in large numbers. But their populations quickly rebound.

Birds: Nesting birds are usually unaffected. Flooded fields may provide more foraging grounds for migratory species.

Fish and other aquatic animals: Rely on floods to replenish populations.

-- source: Manitoba Conservation

Republished from the Winnipeg Free Press print edition April 29, 2011 A4

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