At the end of July, over 850 dead unspawned salmon were found in Alaska. However, the estimated size of the die-off is likely at least four to ten times higher. More varieties of salmon were affected, including pink, sockeye and Atlantic salmon.
Please also read: How we contaminate Europe’s marine environment
When scientists investigated the possible cause of die-off, they were able to exclude parasites, lesions or infections. In fact, the fish even had healthy eggs inside them. However, the die-off coincided with an unprecedented heat wave, leading scientists to believe that this was the cause of the die-off.
On the 7th of July, the water temperature of an Alaskan stream reached a new record – 27.6 °C. As if the new water temperature record was not scary enough, the warming is also occurring at a much faster rate than scientists predicted. In 2016 a study predicted how Alaska’s climate would change in the future due to global warming. Shockingly, 2019 temperatures exceeded the expected values for the worst-case scenario in 2069. This clearly shows that climate change is likely occurring even faster than scientists predicted. Therefore, action to halt it is urgent.
Warmer temperatures affect salmon in various ways. In some streams, salmons don’t have enough energy to spawn. In others, the heat physiologically prevents them from getting enough oxygen moving through their bellies.
Salmon are also suffering from overexploitation, a common issue for many fisheries. However, with intense management of their populations to prevent overfishing, there is hope for their recovery. For example, in Alaska’s Bristol Bay, the salmost are returning and their populations booming.
The question for us is: If rising water temperatures cause a salmon die-off in Alaska, what is the effect on European fish species? Let us know, if you know anything about it!