Sea Lions' Appetite for Young Salmon Higher Than Previously Believed

The precarious decline of wild Chinook salmon in the Pacific Northwest has long been a puzzle for conservationists. A key factor may be the region’s growing population of Steller sea lions. To investigate, scientists in Washington State employed a clever technique: analysing DNA from sea lion scat to reconstruct their diet with a method called DNA metabarcoding.

Their modelling suggests that between December 2020 and August 2021, the sea lions consumed an estimated 284 metric tons of Chinook salmon. Crucially, a large portion of this was made up of the most vulnerable 'ocean age-0' salmon—fish in their first year at sea—totalling over two million individuals.

While the researchers caution that their models have a high degree of uncertainty, the results indicate that sea lion predation is contributing to the low marine survival of young salmon more significantly than previously believed. The study highlights an urgent need for more research into the complex predator-prey dynamics shaping this vital ecosystem's organisation.