Researchers gain insights on Iliamna Lake salmon populations

The Bristol Bay commercial fishery is the world’s largest producer of wild sockeye salmon. Alaska Sea Grant-supported researchers are working to provide new information for the region’s fisheries managers to understand trends and anticipate changes to the sockeye salmon fish populations. 

The scientists are using long-term data of field observations, satellite imagery, and community ice observations in one of the lakes in the area to investigate how fish populations respond to environmental changes, including lake temperature and timing of spring ice breakup.

“Understanding changes in Bristol Bay’s lake ecosystems and how different species have responded to these changes in the past can help us better understand and predict how commercially important species like sockeye salmon might respond to future changes in these critical nursery habitats,” said Curry Cunningham, the principal investigator on the project and an associate professor of fisheries at the University of Alaska Fairbanks.

The study is determining which years and environmental conditions support the greatest sockeye salmon growth, and whether optimal growth conditions differ among other fish species. Researchers use satellite-derived ice data to describe changes in the timing of spring ice breakup and fall freeze-up for lakes within the Bristol Bay region.

“Shifting environmental conditions could affect the growth of juvenile sockeye and competition with other dominant species, like sticklebacks,” explained Elena Eberhardt, a UAF graduate student working on the project. “Understanding how ice cover and temperature are influencing sockeye population dynamics is critical.”

When lakes in high latitude systems thaw in the spring, it starts a period of high productivity that supports fish growth, including juvenile sockeye salmon. The summer growing season likely regulates the growth potential for juvenile sockeye salmon, which can have cascading effects on survival during the freshwater and subsequent marine phases. 

Last August, the researchers conducted an annual surface trawl and beach seine survey at Iliamna Lake to capture and index juvenile sockeye salmon and resident fish species. Within Iliamna Lake, juvenile sockeye salmon share habitat and prey resources with the smaller threespine stickleback. Threespine sticklebacks have a wider thermal tolerance than juvenile sockeye salmon and the team is hoping to identify whether they may be responding differently to environmental changes. The researchers are analyzing the long-term surface trawl data to investigate changes in juvenile sockeye salmon body condition and relative abundance, as well as to explore the effects of increased threespine stickleback relative abundance.

To investigate how changes in the environment have affected the Iliamna Lake fish community, the team identified datasets of spring ice breakup, summer cumulative wind speed, and summer average air temperature for use in the analysis. The researchers are relating these environmental variables with juvenile sockeye salmon relative abundance and body condition.

“It is a unique opportunity to be able to leverage such a long term dataset,” said Eberhardt. “Through our collaboration with the University of Washington’s Alaska Salmon Program, we can analyze changes in juvenile sockeye salmon and other species within the lake over time through the consistent surface trawl surveys that have been conducted annually since the 1960s. By observing how the environment has influenced changes in juvenile sockeye salmon growth, size, and abundance in the past, we can be better prepared to identify how environmental changes may influence sockeye salmon in the future.”

The research team will return to the Iliamna Lake Bristol Bay field station this summer to sample fish, zooplankton, and collect environmental data. They will also share research findings with Iliamna Lake residents in the community of Pedro Bay, who have experienced changes in the lake ecosystem firsthand, and discuss future research.

More information on the project, quantifying the influence of environmental conditions on potential trophic interactions and growth of juvenile sockeye salmon and threespine stickleback within Iliamna Lake, is available on the Alaska Sea Grant website.