In November 2021, nearly an entire run of spawning adult Chinook Salmon died in the San Francisco Estuary — just one of several recent local mass mortality events. As water warms it holds less oxygen and often falls into hypoxic conditions. Both higher temperatures and diminished oxygen levels stress fish, and together they are often deadly. This project aimed to illuminate how Chinook salmon smolts and juvenile Delta smelt tolerate hypoxia across a range of temperatures, which meant first understanding some basic data about these species’ metabolic needs.
To illuminate how Chinook salmon smolts and juvenile delta smelt tolerate hypoxia across a range of temperatures, scientists need to use a technical method called respirometry, a measurement of oxygen consumption. Delta smelt have long been difficult to study using respirometry because they frequently die during testing, likely because they cannot surface to refill their air bladders. Dr. Kwan redesigned and validated a methodology that allows the measurement of delta smelt respiratory parameters by including an air pocket within the respirometry chamber. This enabled the measurement of physiological parameters necessary to create a metabolic index for delta smelt. Additionally, Dr. Kwan conducted a study quantifying how ash from wildfires impacts Chinook salmon after falling into rivers.