VANCOUVER -- So much rain fell in a few days this week that there was even too much water in the rivers for the salmon.
Not only were fish washed onto farm fields and roads when rivers in the Lower Mainland went into flood on the weekend, but surging waters also flushed away an unknown number of spawning beds.
"It was a really localized event and it is almost impossible to evaluate the impact on a widespread basis," Bert Ionson, regional resource manager for the Department of Fisheries and Oceans, said yesterday.
But Mr. Ionson said the floods were so intense that fish were killed and spawning beds ruined.
Heavy rain during the weekend sent several rivers into flood causing property damage and closing roadways.
The most serious damage may have been to salmon stocks, however, because runs of chum and coho salmon are currently in the Fraser River watershed and are moving into tributaries to spawn.
Mr. Ionson said when faced with flood waters fish seek shelter from the current, and that sometimes takes them up onto flat lands next to the river banks.
"I think there is a large number of different impacts from floods," Mr. Ionson said. "You get obvious things like fish seeking refuge and getting stranded [when the water recedes]. When that happens they are obviously not able to successfully spawn."
Mr. Ionson said while people near the flooded rivers saw salmon splashing across roads this week, less obvious was the damage done below the surface to spawning beds where coho, chinook and sockeye salmon have recently laid their eggs.
"During strong events you get a lot of substrate movement [on the river bottom]," he said. "That gravel movement can grind up the eggs or the spawning beds themselves can simply get washed away."
Mr. Ionson said floods also create a lot of sediment that can harm fish in numerous ways, including by settling out on spawning beds, cutting the eggs off from oxygen and smothering them.
Heavy rains started to fall on the Lower Mainland on Friday evening, and continued throughout the weekend. Hydrometric data collected by Environment Canada at river-based recording sites show flow levels climbing Saturday and Sunday, and then spiking with a surge on Monday that lasted through Tuesday.
Mr. Ionson said salmon are adapted to dealing with seasonal floods, and on the Fraser River are often seen turning in to side streams during freshets, where they seek refuge until water levels drop. When the side streams go into flood as well, however, fish face more difficulties.
"But there are always areas where they can find shelter, so it's not 100-per- cent destruction," Mr. Ionson said.
He said many fish may have found shelter in artificial spawning channels, which have been built alongside many rivers in salmon-enhancement projects.
"For the most part those spawning channels are tucked in behind dikes and are protected. There would still be some impacts [from floods] but it wouldn't be as strong."
Author
Topic: Salmon hit by floods. (Read 976 times)