HOMER, Alaska (AP) — The science director for Cook Inletkeeper, a nonprofit organization that monitors the health of Cook Inlet, wrote a paper two years ago on what salmon streams might be like in the future with climate change.
Sue Mauger wrote that water temperatures might rise above 80 degrees (26.67 Celsius) in the next 30 or 40 years.
The future arrived sooner than expected three weeks ago, the Homer News reported.
On July 7, during a “heat dome” of high air temperatures over southcentral Alaska, a real-time stream temperature gauge in the Deshka River registered above 81.7 degrees (27.61 Celsius).
“This is what we predicted, but it’s happening in 2019,” Mauger said. “It’s disheartening to see, getting so high so fast.”
It was the first time that a stream monitored by the group topped 80 degrees.
The Deshka is a tributary of the Susitna River west of Wasilla. The Deshka has the highest king salmon escapement goal — 13,000 to 28,000 spawning salmon — of upper Cook Inlet rivers and streams and produces more than 20% of the chinook escapements for the Susitna River, according to Cook Inletkeeper.
“It’s a big important system,” Mauger said. “It’s amazing to see temperatures in the 80s.”
Cook Inletkeeper previously conducted a five-year study of 48 non-glacial Cook Inlet streams. From that study, the organization selected 16 streams representing a variety of ecosystems and set up real-time temperature monitoring in four: the Deshka, Crooked Creek, the Anchor River and the Russian River.
The Anchor River on the Kenai Peninsula also saw its highest recorded temperatures, hitting 73 degrees (22.78 Celsius). That didn’t stop king salmon from moving upstream to meet the lower escapement goal of 3,800 fish.
For spawning adults salmon or growing juvenile, temperatures above 80 degrees can be lethal. Mauger said the high temperatures make salmon lethargic. Cold water holds more oxygen.
“Really cold water is 100% saturated with oxygen,” Mauger said. “As it warms up, it drops.”
Mauger compared salmon in warm water to Alaskans going to Hawaii in mid-winter.
“It sucks it out of you,” she said. “You lose your appetite.”
Lethargic juvenile salmon become susceptible to predation. The Deskha River has pike, an invasive species more tolerant of heat.
“We may not see the dead juveniles,” Mauger said. “They’re getting scooped up. As they get more lethargic, the pike are enjoying them.”
Spawning salmon need cold water and the high oxygen content as they make their last push up the river to spawning beds, she said. According to fish weir counts on the Deshka River, only 13 salmon had passed in 13 days while water temperatures were high. On July 13, when rain fell and temperatures cooled, 350 salmon moved through the weir.
“It’s likely there were a bunch of them holding low who moved through when things started to cool,” Mauger said.
Spawning salmon have a narrow window to make it upstream to spawn and then another window on the spawning grounds to lay or fertilize eggs. Adults need enough energy to tend eggs before they die.
After salmon hatch, they stay in the river a year or two and could be vulnerable if temperatures rise.
Many scientists attribute declining king numbers to something in the ocean. Mauger and co-authors have submitted a paper for peer review that looks at fresh water impacts, including stream temperatures, flow date, fish runs based on weir counts, flood events, and other factors.
“It’s one of the great joys of the salmon how complicated their life history is, but also one of the great frustrations trying to understand them,” Mauger said. “That is the joy of ecology: trying to understand all those connections, and being really excited when you can find a strong signal.”
Mauger has been studying whether salmon can find cool spots in rivers, such as cuts in riverbanks, shade from trees or groundwater entering rivers.
Deshka River monitoring is funded through a cooperative agreement with the U.S. Fish and Wildlife Service with help from the Alaska Department of Fish and Game and the University of Alaska Anchorage Center for Conservation Science.