The application of road salt to Lower Mainland roads in the fall and winter could be killing juvenile salmon, new research from the University of British Columbia suggests.
That’s according to preliminary results of a study conducted by UBC, Simon Fraser University (SFU), British Columbia Institute of Technology (BCIT) and Fisheries and Oceans Canada, which spent three years looking at 30 streams in the region.
“Adult salmon live in salt water but grow up in fresh, and their bodies change drastically to allow this to happen,” UBC zoology master’s student Carley Winter explained.
“There’s evidence that when salmon are developing at very young ages, death and deformities can occur if exposed to high concentrations of road salt.”
The research team used a network of about 40 water quality monitors across the region to spot spikes in salt contamination, then simulated those conditions on salmon eggs and juvenile fish in a lab.
They found the largest “pulses” of salt in stream water, which lasted for about a day, were about 10 times the acute water quality guideline for chloride in freshwater streams, which works out to be about 30 per cent of the salt content in seawater.
In the lab, they found applying similar 24-hour salt pulses to freshly fertilized embryos “significantly decreased” survival.
Salt pulses eight times the B.C. chloride guidelines resulted in a 70 per cent egg die off. About four per cent of fish that hatched from eggs that survived a salt pulse three times the guidelines had fatal deformities.
“Our data suggests that salting roads at current levels in November or December, when many salmon species are spawning and embryos are developing in streams, could be dangerous to coho and chum salmon,” Winter said.
The team noted the results are only preliminary, and have yet to undergo peer review. But they said the research also suggests changes that could be implemented immediately.
UBC zoology master’s student Clare Kilgour, who also worked on the project, said one key recommendation is the importance of using the minimum amount of salt needed to keep roads and surfaces safe.
“You only need about two tablespoons per square metre,” she said.
“When you’re salting your driveway, spread salt out rather than placing it in clumps. This achieves the same effect but uses much less salt.”
The researchers also recommend cities switch to brine for more of their road-clearing work, which uses half as much salt but can be more effective at sticking to streets and sidewalks.
The team plans to continue the research, looking at how excessive salt levels may affect salmon and eggs in non-lethal ways. A partner team at SFU will also look at how road salt affects juvenile coho salmon next fall.