Thaws Can Be Dangerous to Fish

THE LAKE NEWS Lake Cowichan, BC Wednesday February 22, 1989

Thaws can be dangerous

This article was written in 1989 and we seldom get serious spells of Arctic air on the coast in these days of California Winters but this article is worthy of re- posting because we tend to forget that was still live in Canada and winter can return with a vengeance without much warning and cause serious problems when it leaves.

By Ted Burns

The current spell of cold wea­ther(1989) has ceased at last and the way it ends is very important to the billions of trout and salmon eggs incubating in the gravel of Cowichan watershed streams.

A quick thaw with very mild air and heavy rain could bring disas­ter. Such an event occurred in

January, 1986, with horrendous results. When spring breakup approa­ches in the interior, forest com­panies usually suspend hauling until the roads dry out somewhat. Of course, conditions are gen­erally much worse there because the frost gets deeper into the soil. But in years like this one and that fateful year of 1986, it can be almost as bad on the coast; even worse when the thaw is rapid and heavy rain is involved. Local companies should shut down haul­ing when this occurs because it may make a large difference in the survival of trout and salmon eggs.

It began in November, 1985, when Arctic air spilled out of the interior, quickly freezing wet ground. About that time it be­came evident that the coho run was going to be large. The cold weather persisted throughout the early run and, just as most of the late run was spawning, the weather changed.

A series of mild storms from the southwest arrived, quickly melt­ing snow right to the mountain

tops and thawing ground that had been frozen for more than a month.­

On January 18, almost no snow was left in the mountains and all local streams were in flood and carrying heavy sediment loads as rapidly thawing soil washed into the creeks.

Robertson River suffered the most. The main line logging road (termed Hillcrest Main by some) contains a good deal of fine sand, silt and clay, which had been wet prior to the cold spell and froze solid. When this material thawed, it lost its consistency and the road turned to mush. Trucks continued hauling right through the mess and this didn’t help. Indeed, it made things much worse.

The extent of the damage wasn’t readily apparent although it was obvious that conditions had been severe. When Cowichan Lake Salmonid Enhancement Society volunteers began assessing fry salvage needs on the lower Rob­ertson a few months later, the extreme impact of the thaw was clear. Where there were normally upward of 100,000 fry, there were almost none.

It was possible to walk and wade hundreds of metres and not see a single fry. The losses were stag­gering. Conditions weren’t much better in other tributaries of Cow­ichan Lake like Meade and Sut­ton creeks. Sediment, a high pro­portion from logging roads, had smothered nearly all the eggs of a very good Coho return which was possibly the best since the 1970’s.

Lake News Column

February 22, 1989

Ted Burns


Leave a Reply