Scientists are finding an unlikely source for tracking the health of the Pacific Ocean: decades-old cans of salmon.

A new study highlighted by ScienceDaily analyzed canned salmon collected in Alaska between 1979 and 2021 to study long-term changes in marine ecosystems. Researchers examined 178 cans containing four Pacific salmon species and counted tiny parasitic worms known as anisakids.

While parasites in seafood may sound alarming, researchers emphasized that these worms are harmless when fish is properly cooked or commercially canned. According to the study, anisakids actually play an important role in ocean ecosystems because they rely on multiple species to complete their life cycle, including krill, fish, and marine mammals.

The researchers found that parasite levels increased over time in pink and chum salmon, while remaining stable in sockeye and coho salmon. Scientists say this could indicate that parts of the marine food web are functioning well or recovering after decades of environmental pressure.

One possible explanation is the recovery of marine mammal populations following conservation measures such as the U.S. Marine Mammal Protection Act of 1972. Marine mammals are the final host in the anisakid life cycle, meaning healthier populations can support more parasites throughout the ecosystem.

The study also suggests that archived food products, including canned fish, may offer scientists a valuable way to study long-term environmental change using samples that already exist.

Researchers from the study say the findings help provide a clearer picture of how marine ecosystems have changed over the last four decades, while also demonstrating that even old pantry items can become useful scientific records.