The numbers of Chinook Salmon have dropped drastically in the recent years. In Columbia, US, 17 million salmon used to return each year, but now the number is reduced to just one million. Salmon are an important food source for many animals, both terrestrial and marine, such as bears, eagles and killer whales. As a result of the decrease in salmon population, the killer whale populations are also struggling, as fewer calves survive.
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There are more reasons for such dramatic declines, but it seems that the main two are climate change and dammed rivers. Dams make salmon migration upstream to spawn much more challenging despite fish ladders that enable them to pass the dams. Dammed rivers have very different characteristics from wild ones . They have slower current and warmer water, which both negatively affect salmon migration.
Effects of climate change on salmon
Climate change makes this situation worse. The temperature of the rivers that is already increased because of dams increases even further, negatively affecting salmon. However, the situation is no better in the ocean. Marine heatwaves occur with increased frequency, reducing salmon’s prey and hence their survival. Because the heatwaves are so common, as soon as the chinook salmon population recovers from the previous one, it is stressed again by the next heatwave. Furthermore, “the Blob”, an unusually warm patch of water, is moving through the Pacific. When fish find themselves in the blob they are again experiencing stress from excess heat.
Climate change is also affecting European rivers. A recent report on climate change in Lower Saxony shows that the average annual temperatures there have increased by 1.5°C since 1881. Additionally, the precipitation has already increased and is likely to continue increasing with climate change by 8%. This leads to slight decrease in the annual water balance, but the summer water deficit is increasing, leading to more frequent droughts. Such changes in climate also impact river temperatures in Europe, likely negatively affecting the wildlife that live in them.