High fish mortality rates possible after record-breaking B.C. floods

Pacific salmon are at particular risk as fast-moving flood water can displace eggs laid in the fall and expose them to hungry predators.

Several species of fish could suffer high mortality rates as a result of catastrophic flooding in southern B.C. last week, warn some experts and observers.

Pink salmon are at particular risk, said biologist Marvin Roseneau, as they spawn at the main stems of the now-swollen Fraser and Vedder/Chilliwack rivers.

Most of their eggs were laid in the fall and hidden in the gravel to incubate until spring hatching.

“The floods would have scoured the gravel out almost certainly,” he explained.

“Once the embryos are washed out of the gravel, predators eat them, they get smothered — it’s over for them.”

Roseneau, who teaches fish ecology and management at the BCIT, said Chinook, coho and steelhead salmon may be impacted to a lesser extent as well.

“We will quantify it a year and a half from now when the adults come back. We’ll see whether or not those runs have absolutely collapsed as a function of this event.”

He estimated salmon mortality rates in the low millions for juveniles and the billions for embryos, while clarifying that not all fish and eggs would have survived anyway, due to other natural causes.