A former graduate student in biology at the University of Utah has just published the largest study to date of salmon movements in Alaska.
Sean Brennan is now doing his postdoc work at the University of Washington. He navigated a huge portion of the Nushagak River in Western Alaska over a 3-year period collecting one unique bone called the otolith, which is the ear bone, from 255 Chinook salmon.
“You know fact that every fish has this little chemical recorder inside its head is a boon to scientists who are interested in reconstructing those movement patterns for different conservation issues,” says Brennan.
Diego Fernandez is a U of U research associate professor of geology and geophysics and a co-author of the study. He says they cut through each ear bone layer by layer using laser ablation building a very detailed map of where each fish in the study has traveled and how long it stayed in each place.
“Each season you add a new layer so you end up with something that looks like a tree ring in the sense that it has like bands. Going from the center to the outside of the bone you are basically following all the life history of the fish,” says Fernandez.
“What Sean did that was different than anyone else was to analyze so many samples that you could begin to think about this at a population level.”
That’s Thure Cerling, distinguished professor of geology, geophysics and biology at the University of Utah and co-author of the study. He says what Brennan did was logistically incredible because there are no roads or trails anywhere near the watersheds.
Brennan says he was fortunate to be able to study such a complex organism and hopes the research helps protect the salmon and its habitat.
“The local people on the Nushagak River are welcoming and we worked closely with the folks that actually live in the watershed and their help along the way was invaluable,” says Brennan.
Results of the research can be found in Science Advances.