Winter road salt could be killing salmon eggs

Researchers have found that high levels of salt kill fertilized coho salmon eggs, raising concerns about the use of road salt in winter.

The Road Salt and Pacific Salmon Success Project, a collaboration between UBC, SFU, BCIT, the department of fisheries and oceans, and community scientists, monitors salt levels in more than 30 streams in Vancouver’s Lower Mainland (VLM) . In this Q&A, zoology masters students Carley Winter (CW) and Clare Kilgour (CK) discuss the project’s preliminary results.

Why are you investigating road salt and salmon? 

CW: We launched this project three winters ago to understand the impact of road salt run-off on salmon in freshwater streams throughout the Vancouver Lower Mainland. We know that Pacific salmon are in decline and we don’t know all the factors involved. Adult salmon live in salt water but grow up in fresh, and their bodies change drastically to allow this to happen. 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.

CK: Federal and provincial guidelines set maximum salt, or chloride, levels in streams, but these levels have not been widely and routinely monitored in VLM streams. We used a network of almost 40 water quality devices across the VLM to identify any patterns in road salt contamination, and specifically, whether there were spikes in conductivity occurring every winter when road salt is being applied. Then, we tested in the lab whether these levels and patterns affected salmon at the ages when they would live in these same streams and rivers; that is, salmon eggs and fry. 

What did you find? 

CK: Our results are preliminary and so, yet to be peer-reviewed. We measured conductivity in streams, a proxy for salt levels, and found there were indeed peaks in the winter. The largest ‘pulses’ of salt were 10 times B.C.’s acute water quality guideline for chloride in freshwater systems, equivalent to almost 30 per cent of sea water. When these pulses occur, they exceed this acute guideline just over 30 per cent of the time. On average, these excessive salt levels lasted for about a day.

CW: We mimicked these recorded salt pulses in the lab, exposing coho salmon eggs to one salt pulse either shortly after fertilization or once they hatched. We found applying a 24-hour salt pulse to embryos shortly after fertilization significantly decreased survival, starting at two times the recommended chloride levels. When salt concentrations increased to eight times the guideline level, more than 70 per cent of eggs died. If embryos survived a salt pulse of three times the recommended level, we found about four per cent of them were deformed and would not survive in nature.

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. 

What can we do?

CK: It’s important to keep people safe from slipping and falling during winter. Rather, we should use only the amount of salt needed to melt ice: you only need about two tablespoons per square metre. 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.

CW: Municipalities could switch to brine for melting ice on roads as it not only uses up to 50 per cent less salt, but it is more effective at sticking to streets and sidewalks. It’s a win-win: Using less road salt saves salmon and taxpayers’ money.

What are your next steps?

CK: We plan to investigate how excessive levels of salt affect salmon eggs and fry in non-lethal ways, for instance, growth and genetic effects. Our partners at SFU will look at how road salt affects coho hatching in the field next winter.