Road salt creates a slippery slope for pacific salmon: Environmentally realistic salt pulses have lethal and...

Road salt, primarily sodium chloride (NaCl), is frequently used as a de-icer during cold seasons. In the Vancouver Lower Mainland (VLM) region of British Columbia, Canada, road salt is contaminating local streams where Pacific salmon spawn. The provincial acute water quality guideline is 600 mg L^-1 Cl^-, yet road salt contamination is resulting in pulses of salinity estimated to exceed this guideline by over 11-fold. In the VLM, the spawning and subsequent rearing period of coho salmon (Oncorhynchus kisutch) directly overlaps with these pulses of salinity. This study investigates the lethal and sublethal effects of road salt pulses on coho salmon by simulating an environmentally realistic pulse of road salt at different stages of development. We exposed coho embryos to a 24-h salt pulse at six environmentally relevant salt concentrations at <1 h post-fertilization or at 50 % hatch. To investigate effects on fertilization success, we conducted a 5-min salt exposure at the time of fertilization. Following salt exposures, coho were returned to freshwater to rear until swim-up to assess survival and the presence of deformities. There was no effect of salt exposure on fertilization, but the <1 h post-fertilization exposure group was sensitive to a salt pulse, as there was significant mortality, persistent ionoregulatory disruptions, and an increase in deformities. Upon hatching, exposed embryos exhibited a decrease in body length and larger yolk sac volume, suggesting that the early salt pulse disrupted embryonic development. Our research highlights an urgent need for improved road salting practices to protect developing coho salmon.