Checking the pulse of Idaho's salmon and steelhead runs

Doctors start assessing our health by counting the number of pulses we have in a minute. When it comes to Idaho’s migrating salmon and steelhead, we can get a quick idea of the health of the populations by counting the number of fish passing dams on their migration. Like a pulse, it doesn’t tell us everything, but it is a good first cut at how healthy our fish populations are. Let me explain a little about how dam counts are done, and how we use them to track the health of our salmon and steelhead populations.

How it's done 

Counting fish at dams has been around a long time. When dams were first built on the big rivers in the Pacific Northwest, fish ladders were a new idea. No one was sure how well they would work at letting fish swim past a dam. In the early days, counting fish swimming up the ladder ensured fish ladders actually worked, and it also tracked the health of the salmon populations upstream. 

Even today, counters trained to identify salmon and other fish species observe a window showing the inside of a fish ladder. They use mechanical counters to keep track of fish swimming upstream and subtract any fish seen going downstream. Fish are counted from April through October for 16 hours a day. Fish counting staff are hired by the Army Corps of Engineers, who operate the dams between Idaho and the ocean. Before April and after October, counts are made using videos. Videos are also made during the night when large numbers of fish are expected, usually during summer.

Counts began at different times at different dams. Bonneville Dam is the oldest on the Columbia River, and its count began in 1938. It was not possible to count salmon entering the Snake River until 1962, after Ice Harbor Dam was completed. The counting point got closer and closer to Idaho in 1969 (Lower Monumental Dam) and 1970 (Little Goose Dam), until 1975 when Lower Granite Dam was finished about 40 miles downstream of the Idaho boundary. Because this is the last dam salmon pass on the migration up the Snake River, these counts give us the best estimate of the number of fish about to enter our state. 

What we do with the counts

Fish and Game biologists summarize and report counts of wild spring and summer-run Chinook Salmon, wild steelhead, Sockeye Salmon, Coho Salmon, and Pacific Lamprey. We compare these counts to what a minimum run size should be and also to what should be typical of a healthy population, which is the real goal. Fish and Game also collects other information at the fish trap at Lower Granite Dam, like a doctor will run other tests if the pulse is not good. 

These collections started in fall 2008 and allow us to look at things like the age structure and genetic background. Age structure is how many of the population fall into different ages, which can signal problems when it becomes skewed. Genetic background helps biologists assign fish to the population they are returning to. These things are particularly important for wild fish. 

A window in a fish ladder to count fish is a very low-tech way to count migrating salmon and steelhead, but it remains an important technique to help us check the pulse of Idaho’s salmon and steelhead populations.