Strontium allows for mapping of salmon migrations

New Scientist : Small calcium carbonate deposits called otoliths form in the inner ears of salmon as they age and collect trace amounts of other elements in the water. As otoliths grow, they create layers similar to tree rings. Sean Brennan of the University of Alaska Fairbanks and his colleagues have now used the strontium isotopes in those mineral records to map where individual Chinook salmon have been and for how long. Strontium, which lies below calcium in the periodic table, dissolves out of river rocks, and different regions have different isotope concentrations. Using water and other samples they took from the Nushagak River in Alaska, the researchers were able to determine the exact birthplaces of more than 400 salmon caught in 2011. They also found that 70% of the fish stayed in the same stream they were born in, with the rest migrating to other habitats.