Salmon have ears. And they grow like trees.
While salmon themselves use their ears for hearing and balance much the way humans do, scientists recently found a way to put this puzzling appendage to use for improving conservation strategies. By taking advantage of chemical traces in the tree-like growth patterns found in salmon ear bones, researchers can precisely trace a salmon's life history, from the tiny tributary it was born in to the open ocean. The work was published today in the the journal Science Advances.
Salmon ear bones, called otoliths, grow differently than the bones in your body do.
"It has rings that correspond to different times in a fish's life," lead study author Sean Brennan of the University of Washington said in an interview. "The inner rings correspond to the fish's earlier life, and the outer rings correspond to progressively later times in the fish's life."
As the salmon swims about, its ear bone keeps growing and captures chemical traces from the environment within it. Since the ear bone is conveniently organized into chronological layers, scientists can get a sense of where the fish was at what time by slicing it open and comparing the different chemical traces found in different layers.
In this case, Brennan and his colleagues looked at the levels of different types of the element strontium in the ear bones. They mapped where these chemicals are found over a large area, and then matched the chemicals found in the ear bones to places on the map.
These location-linked chemical cues are particularly useful when studying migratory animals like salmon. Because they're tough to keep track of, figuring out which habitats they use and need to survive is a major challenge for conservation efforts.
"Mobile species like salmon are really hard to study," says Brennan. "Being able to identify critical habitats is really important for developing conservation strategies."
This tracking technique is not specific to salmon, according to Brennan.
"You can use this tracer to study a wide range of animals," he says. "A map developed for salmon can also be used for caribou."
The work shows that it is possible to learn about a salmon's life by peering in its ear, but Brennan notes that putting this strategy into practice remains a hurdle. "Since this is a new tool, there's still a lot of work that needs to be done to integrate this technology into management strategies at local fisheries."
The Science Advances article can be found here.
Photo: Kai Schreiber | Flickr
