Ocean heatwaves have been well documented in recent years. Now, scientists say river temperatures, too, are soaring – leaving Alaska’s world-famous salmon to navigate increasingly challenging waters as they struggle to complete their migratory cycle. When circumstances deteriorate, migrating fish are often forced to keep moving until they find cooler water. Now, changes in salmon populations are already affecting the culture and lifestyle of many coastal native tribes, a connection that goes back thousands of years.

Salmon are anadromous fish, meaning they spend parts of their lives in different habitats. Alaska’s rivers are home to all five species of Pacific salmon; pink (humpy), chinook (king), coho (silver), sockeye (red) and chum (dog). Although there are differences between them, they are all born in freshwater and spend some time there before heading to the ocean, which has better resources for them to eat and grow. When ready, they return to the same stream they were born in, to reproduce and then die.

Salmon go back to their home river because it usually gives them the best chance of survival, says Peter Westley, associate professor of fisheries at the University of Alaska Fairbanks. “Different rivers have different factors, like temperature and how much water is in it, and how big the rocks are – all kinds of stuff. So, the fish that were born there and survived there have traits that allow them to do well there.”

Read the full article at BBC News