The heavy rainfall that turned rivers and creeks into raging waterways this week is expected to have a significant effect on salmon stocks for years to come.
The swift water likely swept away incubating eggs and sent young salmon prematurely out to sea, destroyed critical gravel nesting sites and food sources, and hindered salmon that had yet to spawn, says Ian Bruce, a biologist with the Peninsula Streams Society.
“It will affect a lot of fish,” says Bruce, who was assessing some of the damage caused by overflowing creeks and streams this week.
The society’s fishway project on Millstream Creek spilled its banks, spreading water and debris into the forest along Atkins Road.
It wasn’t immediately clear how many juvenile fish or eggs might be affected by the deluge.
The Department of Fisheries and Oceans is expected to have scientists on the ground at Island rivers and streams, along with those elsewhere in B.C., over the coming days to watch flows and assess impacts on the spawn.
Bruce, who provides fisheries services to governments and First Nations, said he will book an airplane this week to survey the overflows and potential damage to fish stocks in fledgling salmon-bearing waterways in the capital region like Colquitz, Craigflower and Hagen Graham watersheds, as well as the Goldstream River.
The Goldstream Hatchery in Langford has concerns the chum salmon run might have been wiped out. It had already been one of the lowest returns of chum on record, and the hatchery was only able to collect about 45,000 eggs. In other years, it has collected close to 600,000 eggs.
Peter McCully, a technical advisor at the hatchery for 40 years, said it’s the worst flooding he’s ever seen. “I’ve seen the Goldstream flood before, but never like this,” he said.
Incubating eggs are being smothered in silt and debris. The hatchery’s fish fences and weir used to count fish and collect selected brood stock was completely submerged and weighed down by logs and debris. A hydrometer system used by the Capital Regional District to measure water flows was ripped off its foundation and deposited downstream.
The extent of the damage won’t be known until the river flows subside. McCully said crews may get out to assess the damage on Saturday if the flows have subsided enough to make it safe.
McCully said “a significant number” of coho eggs were collected by the hatchery prior to the heavy rains, as that species spawned earlier than the chum.
The chum salmon, however, are a concern, he said. The lower chum counts are the same on all major rivers on eastern Vancouver Island, he said, and extend to the Gulf of Alaska. A colleague in Japan told McCully that chum runs are low there as well.
Fisheries and Oceans Canada had warned in a report two years ago that climate change was already affecting stream flows and salmon runs.
The State of Canadian Pacific Salmon report said coastal B.C. river systems are seeing more flash flooding, leading to increased egg losses in what biologists call “scouring,” where swift flows are raking the river beds where salmon lay eggs. Droughts are also becoming more frequent, creating migration barriers to salmon and increasing losses of incubating eggs and juveniles.
The federal agency said erosion and landslides are also increasing within watersheds, with hillsides more vulnerable to landslides amid more prolonged periods of rain and warming temperatures.
Increased sediment flowing into salmon-bearing watersheds reduces the quality and amount of spawning ground and juvenile-rearing habitat. Along with smothering incubating salmon eggs, sediment can eliminate deep pools that offer juveniles relief from higher temperatures.
Bruce said the deluge this week washed away gravel beds containing incubating eggs, especially in areas where river banks have been altered for farming and development and the river can no longer spill its banks.
“Flood plains around rivers allow the fish to find their way back. They slow down the water … store the water until it returns to normal.”
These types of flooding events “are going to keep happening,” said Bruce.
The Peninsula Streams Society said one outlet for water so urban streams don’t overflow is “rain gardens,” catchment ditches with plantings that collect runoff.
The society has partnered with the Friends of Bowker Creek to create 1,000 rain gardens that mitigate flows into local creek systems.
In September, the Peninsula Streams Society brought in loads of gravel to prepare a section of Bowker Creek for chum eggs.
The eggs were placed in two “salmon condos,” plastic structures with grates buried in the gravel that protect the eggs but allow the hatched fry to swim free. The eggs were taken from salmon at the Goldstream Hatchery in Langford.
Despite heavy flows this week, Bruce said the nesting site was undisturbed because it had been placed in a back eddy of the creek.