This summer’s weather has been rough on Alaska and its wildlife. In all corners of the state, there has been unusual weather events that have disrupted and threatened Alaskan wildlife. Rainstorms have pummeled the western coast, wildfires have swept through southcentral, and lightning has struck in the arctic ocean. This summer has also delivered record high temperatures and drought conditions for the sub-arctic that was the likely cause of a mass die-off of Chum salmon (Oncorhynchus keta) along the Koyukuk River.
Air temperatures along the Koyukuk river, near Huslia, Alaska, rose to 89 to 90 degrees Fahrenheit between July 7th through July 11th, at the same time water levels were extremely low. By the 12th there were sightings of dead chum salmon along the river. It is highly likely that the combination of low water level and high air temperature increased the water temperature to the point of being unhabitable for chum salmon. Further evidence to support this hypothesis came from a team of researchers led by Dr. Stephanie Quinn-Davidson, the director of the Yukon River Inter-Tribal Fish Commission, who arrived on the river about two weeks after the first sightings were recorded.
Dr. Quinn-Davidson’s team surveyed a 200 mile stretch of river and counted 850 dead chum salmon along the shoreline. The research team counted salmon as they boated upriver and stopped when they spotted large groups of salmon along the shore. Dr. Quinn-Davidson’s team examined the chum they found on shore to determine the overall health of the salmon before death. The salmon that the researchers sampled were in good condition before the die-off, as they found eggs and milt in the chum and they did not observe any lesions, parasites, or tumors. The number of dead salmon physically counted is likely to be a small fraction of the salmon killed by the heatwave, as most salmon would have either sunk to the bottom or been swept downriver.
The only species observed to be affected in this event were chum salmon. No dead King salmon (Oncorhynchus tshawytscha) were found and only two pike were observed to have died in the timeframe of the extreme heat event. The chum salmon likely died because of their smaller size and smaller fat stores. As salmon re-enter river systems, they stop eating and begin to burn their fat reserves to help them get upstream and prepare for reproduction. As temperatures rise, the metabolism for all living beings rises as well which burns more energy stored in the body as fat. Due to the condition that the chum were found in, the likely cause of death would be that most of the salmon simply ran out of energy due to heat stress. The King salmon with their larger bodies were likely able to survive the extreme heat event due to their larger fat stores.
Unfortunately, the Koyukuk river has not been the only river system experiencing a combination of high temperatures and low water levels due to a lack of snowpack from the winter and a lack of rain this summer. As a result, the Deshka and Little Susitna rivers have been closed to fishing for Coho salmon by emergency order from the Alaska Department of Fish & Game. There has also been a report from a local environmental observer that Jakolof creek near Seldovia has dried out leading to a mass die-off of stranded salmon.
As our climate continues to shift, Alaskan wildlife will experience more stressful events that are beyond their control. There are some actions we can take in specific areas to help mitigate the effects of a changing climate on wildlife. In this case there is little we can do to increase the amount of precipitation to keep our rivers running, but we can provide shady areas to help salmon stay cool. One proposal is to strategically planting trees along riverbanks, in eddies and bends to provide cold water refuges for salmon as they journey upriver.
Reporting changes in the environment or abnormal wildlife behavior is just as important as direct action. If you see something off in your environment, please report it to the Local Environmental Observers network at leonetwork.org . If you happen to witness wildlife behaving abnormally or a mass-die off you can report it to leonetwork.org or to a wildlife biologist at your Fish and Game office. Timely and accurate information are vital to protecting our environment and the wildlife that we share it with. If you see a large dead salmon please conduct a survey or contact a wildlife biologist. Relevant data to collect would be a total count, sex, photographs or video, check for pale gills, any sign of infection, disease or parasites and condition of belly fat. For more information please visit https://www.leonetwork.org/en/docs/about/leo-webinars.
Sam Bundy, Environmental Program Assistant