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Conservation efforts do more harm than good

Primary culprits are humans and a little shrimp introduced to the lake by man many years ago

by Judie Steeves
Staff Writer, Capital News
Friday, December 15, 1995

There’s no argument amongst the technical experts that Okanagan Lake no longer has the capacity to maintain life that it once did.

Primary culprits are humans and a little shrimp introduced to the lake by man many years ago.

Within the last two decades, Kokanee stocks have declined dramatically and Rainbow stocks would also appear to be at risk,” reports Bruce Shepherd, fisheries biologist with the regional office of the environment ministry.

His words are contained in the draft of a lengthy and detailed report from a panel of scientists with various areas of expertise relating to lakes, called together last summer in an emergency session to brainstorm on the problem in Okanagan Lake and possible solutions.

The disappearance of the Kokanee alerted the public to the problem but the solution is less clear.

Although we’re conditioned to believe a lake of crystal clear water is the ideal, fish don’t agree with our perception, says Shepherd.

There must be a balance between nutrient-rich lakes and those so crammed with the resulting growth that the oxygen level gets too low for other organisms to survive.

In Okanagan Lake right now that balance does not favor fish.

To better balance the nutrient levels in that lake either nitrogen and phosphorus must be added to it, or the Mysis relicta, the small shrimp introduced, ironically, by the provincial fisheries branch three decades ago as food for Kokanee, eradicated, says the report’s coauthor, Ken Ashley, a research biologist at UBC.

The good news is there’s hope it might not be as difficult as he once thought, to reduce the populations of that thriving shrimp, says Shepherd.

The realization that Mysis shrimp do not “breed like flies,” but have a limited capability of producing perhaps 9O young in a few years encouraged Shepherd, since any disruption could make a significant difference in their populations.

(Their competition with young Kokanee for the same feed is one of the main limiting factors in the population of those land-locked salmon in Okanagan Lake.)

That lends credence to a proposal to use aerators to raise columns of the lake’s water, Mysis in them, from the colder depths of the lake to warmer upper levels where they might perish and be eaten by fish.

Shepherd and Ashley wouldn’t release the 10 recommendations in the report until all members of the technical advisory panel have seen it, and they’ve only just received it, but some will deal with public education.