Written by: John Hargrove

Each year, biologists sample thousands of Chinook salmon and steelhead at Lower Granite Dam as they return to spawning tributaries in the  Snake River basin. This opportunity allows biologists to gather data to better understand salmon and steelhead populations in Idaho. As part of this process, a small piece of their fin, about the size of a pencil eraser, is taken from each fish, placed on a special sheet of paper called Whatman sheets to dry, and are transferred to a genetics lab in Eagle, Idaho to analyze.

Once at the lab, DNA is extracted and the genetic profile of individual fish is compared against several genetic databases. First, we compare each returning adult against a genetic database of hatchery broodstock. This comparison helps us determine if the fish is from a hatchery program. If the fish is not from a hatchery, it is then compared against a genetic database of wild fish from across the Snake River basin. This database is known as a genetic baseline and is comprised of genetically similar populations, also known as reporting groups or stocks. A wild salmon or steelhead is compared against the genetic baseline in an analysis known as genetic stock identification which tells us where the fish was most likely born. Knowing where a fish is from is super helpful because we can describe traits of populations without having to find them on their spawning grounds.

A map of genetic reporting groups for steelhead in the Snake River basin.

Genetic stock identification helps us to understand important characteristics of different stocks. When we combine genetic data with information on when a fish was collected, their age, length, and sex, we can then describe the run timing, age distributions (fresh- and saltwater), length structure and sex ratios of different stocks. These data play an important role in tracking the abundance and recovery of Chinook salmon and steelhead in the Snake River basin!

A steelhead caught in the upper Salmon River.