Scientists found that Chinook salmon’s birthplace and later evolution can be tracked by looking at their ear bone. Researchers explained that the bone can record chemical composition of the water the fish had lived in just like a tree’s growth rings provide hints on dry years.
As the years pass, the fish’s ear bone, scientifically dubbed the “otolith,” gets impregnated with the chemical signature of the environment that hosted fish. As a result, researchers were able to tell where different individuals of Chinook salmon were born and lived in the first year of their lives.
Sean Brennan, lead author of the find and researcher at the University of Washington’s School of Aquatic and Fishery Sciences, explained that the tiny bone acts just like a recorder that holds an archive with the fish’s entire life history.
“Each growth ring is a direct reflection of the environment the fish was swimming in at the time it was formed,”
Dr. Brennan added.
The research team also explained how the otolith keeps a record of the chemical composition of an underwater environment. As Chinook salmon swims in rushing water it absorbs ions of strontium dissolved from the bedrock. Those ions are later deposited onto the bone.
And strontium is a very reliable element to be used as a tracker because its chemical composition does not alter. The element can accurately tell researchers the exact location and time of a fish swimming in a river.
But in order to obtain this data, researchers needed an accurate map of the river system and its variation of strontium. Ions of strontium vary a lot according to the structure and age of bedrock, so there aren’t two rivers with the same composition.
Scientists tested their theory in Alaska because the place is well-known for its rivers’ bedrock heterogeneity. This means that in Alaska rocks differ a lot from one region to another.
Also, Alaska’s Bristol Bay is one of the last locations in the world where wild salmon lives and one of the most populated area with Nushagak Chinook salmon in the world. More than 200,000 Chinook salmon breed in the region. But after they reach maturity they migrate to the Pacific Ocean.
Researchers wanted to learn where exactly Chinook spawned in spring to help conservationists have a clearer view on the factors that affect the fish survival rate. Chinook salmon population sharply declined in the past decade so everybody struggles to find the cause.
As a follow up, researchers plan to analyze traces strontium in the teeth and feather of various species to better understand their migration patterns and chances of survival.
Image Source: Twisted Sifter