Long before humans populated our coastline, millions of salmon returned annually to the waterways of B.C. to spawn. This iconic migration continues today. Salmon are anadromous, meaning they spend the first part of their lives in freshwater, the middle part in the ocean, and the last part returning to the stream where they were born to spawn and die. Five unique species of salmon migrate up B.C.’s inland waterways every year: pink, sockeye, chum, coho, and chinook. Unsurprisingly, species with the farthest trips upstream begin their inland migration sooner; these fish must swim upwards of 1,500 kilometres from the mouth of the river to reach their spawning grounds. Since salmon stop feeding once they leave the ocean, their entire journey is completed using the energy stores they’ve obtained at sea. Salmon have evolved to endure their required journeys. However, with climate change posing increasing stress on our planet, these fish are already being challenged in new ways.
Anyone who has spent time in B.C. lately will have observed that the last few months have been very hot and dry. While we may have appreciated more beach days, this heat has not been good for the salmon. Water in the Fraser River was four to five degrees Celsius warmer than usual this summer. Since less oxygen is available to fish in warmer water, a salmon’s swimming capability decreases because its heart is struggling to deliver sufficient oxygen to its muscles. As such, a fish has to work harder and exert more energy to travel the same distance. Not a huge deal if it’s the 100-metre dash, but a really big deal if you’re travelling 30 marathons without any food. Moreover, diseases proliferate in warmer waters and already many sockeye have been found dead with skin lesions and fungal growths before completing their migration. In addition, the little snowfall we had over the winter meant less new freshwater entered inland streams during spring and summer. As a result, stream water is not just warmer than normal, but also lower than normal — if it hasn’t dried up altogether.
While no two species or populations are alike, research in the last few years has shown that salmon are increasingly affected by climate change. Regardless of the species, all salmon typically have to wait a certain period of time at the mouth of the river while they allow their body to acclimate between fresh and salt water. Research has shown that changing environmental conditions, including temperature, are causing some fish to wait too long before heading upstream. As a result, they do not have enough energy to make it all the way home. For fish that do successfully reproduce, there could be further complications for their offspring. Since the development of young salmon is directly related to the surrounding environment, increased temperatures could result in faster development. This is a problem since these fish may hatch earlier than usual and thus the food resources that are usually available to them as they make their way to the sea may not yet be available at that point in the season. As such, fewer juveniles may make it out to sea, which will have repercussions down the line, with fewer adult fish returning to spawn.
These are just a few of the many challenges facing salmon in the coming decades. That said, not all salmon will be affected by climate change in the same way, and some populations are already demonstrating an ability to compensate for these environmental changes. So, while it’s not all doom and gloom, we still need to make sure we do everything we can to ensure the survival of our salmon.
Blog post by Laurenne Schiller, Ocean Wise research analyst.
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