Canned salmon are the unlikely heroes of an accidental natural history museum in the back of the pantry, with decades of Alaskan marine ecology preserved in brine and tin.
Cans have been out of date for decades
Parasites can tell us a lot about an ecosystem because they are usually involved in the activity of several species. But unless they’re causing a major problem for humans, historically we haven’t paid much attention to them, writes sciencealert.com.
That’s a problem for ecologists like Natalie Mastick and Chelsea Wood of the University of Washington, who were looking for a way to retroactively track the effects the parasites have had on marine mammals in the Pacific Northwest.
So when Wood got a call from the Seafood Products Association in Seattle to see if she was interested in taking the cans of old, expired salmon — dating back to the 1970s — her answer was an unequivocal yes .
The boxes have been shelved for decades as part of the association’s quality control process, but in the hands of conservationists they have become an archive of superbly preserved specimens; not salmon, but worms.
Photo Techno Science
These approximately 0.4 inch (1 centimeter) long marine parasites, anisacids, are harmless to humans when they are killed during the preservation process.
“Everyone assumes that worms in salmon is a sign that things have gone wrong,” Wood said when the research was published this year.
“But the life cycle of the anisakid integrates many components of the food web. I see their presence as a signal that the fish on the plate comes from a healthy ecosystem.”. she said.
Anisakids enter the food web when they are eaten by krill, which in turn are eaten by larger species.
This is how anisakids end up in salmon and eventually in the intestines of marine mammals, where the worms complete their life cycle by reproducing. Their eggs are excreted into the ocean by the mammal, and the cycle begins again.
“If a host is not present – marine mammals, for example – the anisakids cannot complete their life cycle and their numbers will decline,” said Wood, lead author of the paper.
The 178 cans of “archive” contained four different salmon species caught in the Gulf of Alaska and Bristol Bay over a 42-year period (1979–2021), including 42 canned chum ( Oncorhynchus keta ), 22 coho ( Oncorhynchus kisutch ). ), 62 pink ( Oncorhynchus gorbuscha ) and 52 sockeye ( Oncorhynchus nerka ).
Although the techniques used to preserve salmon fortunately do not keep the worms in pristine condition, the researchers were able to dissect the fillets and calculate the number of worms per gram of salmon.
They found that the worms grew over time in salmon, but not in sockeye or coho.
“The fact that their numbers increase over time shows that these parasites have managed to find all the right hosts and reproduce.”said Mastick, the paper’s lead author.
“This could indicate a stable or recovering ecosystem with sufficient suitable hosts for anisakids.”
But it’s harder to explain stable worm levels in coho and sockeye, especially since the conservation process has made it difficult to identify specific anisakid species.
Mastick and their colleagues believe this new approach—dusty old boxes turned into ecological archives—could fuel many more scientific discoveries.
