Water temperature is critical to salmon. It affects their ability to grow, metabolize food and fight off diseases.
If water temperature isn’t cool enough during their life span, the stability of an entire population can be impacted, said Leah Mellinger, Port Gamble S’Klallam Tribe’s finfish program manager.
To better understand this, the tribe is testing the water temperature tolerance of juvenile chum salmon.
“The tribes and Washington Department of Fish and Wildlife are developing a comprehensive chum salmon management plan and one of the big missing chunks is how freshwater degradation impacts smolt productivity and pre-spawn mortality,” Mellinger said.
Climate change also is a motivator for starting the study.
“With changing hydrology and climate, rivers are expected to get warmer,” she said. “It is necessary to understand salmon temperature tolerance to be able forecast run sizes and manage populations.”
The tribe developed a thermal study to test around 2,000 chum from about 20 populations in western Washington.
Within each population, 100 juvenile chum are pulled from a hatchery before their scheduled release or beach seined from a nearby creek during outmigration, to assess both natural and hatchery fish. The fish are dispersed into 32-ounce mason jars placed in 12-gallon tubs filled with local creek or hatchery water.
A heating element slowly increases the water temperature and a pump circulates the water so the temperature increases at a steady rate. Dissolved oxygen is pumped into each jar so that temperature is the only stressor on the fish during the test.
Staff check the temperature every 10 minutes and observe the fish. When a fish flips, indicating it would not recover in the wild, the temperature is noted and the fish is pulled from the jar and placed in a recovery bucket before being released back into the hatchery or stream.
“We just make them a little unhappy for a few minutes and in return, get important information,” Mellinger said. “While there are many factors that play into fish survival, this kind of information is so necessary that you really can’t do anything else without the baseline.”
The fish start the experiment at their local water temperature to minimize stress. Some populations seem to handle more heat than others, Mellinger said, as some flipped at 25° C (77° F) while others tolerated as warm as 28° C (82.4° F).
“If we know the rivers are getting to a certain temperature, we could expect that the production of those fish, either on the escapement side or on the smolt side, is probably going to be a lot lower, and that can feed into forecasting for chum four years ahead,” she said.
Following the juvenile study, the tribe will conduct a similar study on a smaller group of adult chum to see if results correlate.
“If so, then we can extrapolate that out to endangered populations instead of assessing every adult population and potentially adversely impacting ESA-listed stocks,” Mellinger said.
Port Gamble S’Klallam Tribe finfish program manager Leah Mellinger tests the water temperature in jars containing juvenile chum salmon for the tribe’s water temperature study. Story and photos: Tiffany Royal
