An early sockeye salmon run is having trouble making it up the Fraser River and the majority won’t make it to their spawning grounds this year, largely because of the ongoing Big Bar landslide, according to a report from the Pacific Salmon Commission.
Despite tens of thousands of fish passing through sites in Mission and Hells Gate, none have been observed on the other side of the landslide.
“Natural passage has been limited at the slide, and no sockeye salmon have passed the slide at Big Bar to date,” reads a briefing from the Fraser River Panel.
Gwil Roberts with Fisheries and Oceans Canada (DFO) says high water levels have delayed the arrival of salmon at the site of the landslide, where several systems are in place to ensure fish make it past the five-metre waterfall it created.
Roberts, the director of DFO’s response to the landslide discovered north of Lillooet, B.C., last summer that sent 85,000 cubic metres of rock crashing into the river, says the volume of water in the Fraser River at Hope, B.C., which is downstream of the slide was recently measured at about 62 per cent above average.
As a result, Roberts says very few salmon have arrived at the slide, while crews have been forced to relocate some of the equipment to ensure fish passage, though everything remains operational.
Michael Crowe, manager of biological programs for the landslide response, says the salmon are using up their energy reserves and heavy sediment in the river can also damage their gills.
Scott Hinch, a UBC professor of fisheries and conservation, says it was widely expected salmon runs early on this year were not going to be very strong.
“What they couldn’t predict was how high the water discharge was going to be into the Fraser River,” Hinch said.
Known as the Early Stuart run, Hinch says higher than normal flows make it particularly challenging for the fish to swim up river.
“Whenever you see really high flow conditions like this, it usually means that some of the early runs have difficulty getting back to their spawning ground,” he said. “But when you layer the landslide on top of these really high discharges, then you have a real problem.”
Last year 99 per cent of Early Stuart and 89 per cent of early chinook salmon were lost because of the slide.
Big Bar slide
It’s believed the massive landslide north of Lillooet, B.C., occurred in late October or early November 2018, but it wasn’t discovered until last June after fish had already begun arriving.
About 60,000 fish were helped over the slide last year, while 220,000 made it past on their own once water volume dropped, according to officials from the Department of Fisheries and Oceans.
A contract to clear the slide has swelled to nearly $53 million.
Hinch says the run was already under threat due to variable weather conditions that researchers say are consistent with climate change.
“It’s quite a dire situation for that group and other groups that have to migrate past the landslide,” said Hinch. “They’re not the only ones that are designated as threatened or endangered. There are several other populations of sockeye or chinook that are in the same boat.”
If the issue persists across a four year span, the run could collapse, Hinch warns.
“After four years in a row, if the adults don’t make it to the spawning ground, you’ve basically wiped out that population.”
The Fraser River Panel expects total salmon returns will be less than 1 million fish this year — a fraction of historical figures, once as high as 25 million.
The DFO is expected to provide an update on its response to the Big Bar slide on Mon. July 27.
With files from Alex Migdal