Anybody who’s spent some time in Idaho’s wild spaces can tell you that our stream systems come in many different varieties. We have small brooks that trickle over cascading rocks. We have roaring rivers that meander through valleys and slice through canyons. Most streams, however, fall somewhere in between and one of the best things about them is the fish they produce.
What a difference the stream makes for juvenile steelhead
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Steelhead, along with Chinook and Sockeye salmon all rear in these streams as juveniles, but unlike their salmon counterparts which usually spend only one year in natal streams before migrating to the ocean, steelhead often hang around a little longer. Some do migrate out as one-year-olds, however, some may stay in the stream for up to six years before they enter the process of smolting and head out to sea. Why is this? Well… It all depends on the stream.
Steelhead need to reach the right size, about 7 inches, before they head out. In less productive streams, fish grow slowly so they stay in the system longer. In more productive streams, fish grow rapidly and migrate at a younger age.
Take, for example, the differences between Rapid River near Riggins and the Pahsimeroi River south of Salmon, Idaho. Both are tributaries of the Salmon River but the steelhead smolts they produce are very different. This is because the stream environments in which these fish live are quite dissimilar.
Rapid River is less productive than the Pahsimeroi. Rapid is shallow and steep, 22.8 miles long it drops over 4,800 feet from its headwaters to its conjunction with the Little Salmon River. It tumbles down the eastern slope of the Seven Devils mountain range and is largely fed by snowmelt run-off.
The Pahsimeroi meanders through a fertile valley snuggled in between the Pahsimeroi and Lemhi mountain ranges. Largely spring-fed, its longer length of 58.4 miles only drops 3,200 feet in elevation. The fish reared in Rapid River are smaller and migrate at a later age than Pahsimeroi fish which grow very rapidly and migrate out early.
Idaho Department of Fish and Game uses scales collected from migrating smolts to age fish. These ages are used to assess populations and help biologist manage the fisheries. Scale agers use the alternating bands of wide (summer) growth and slow (winter) growth to determine fish ages. As you can see, there’s quite a difference between Rapid River and Pahsimeroi River juvenile steelhead scales. These scales were taken from fish the same size, and at the same time, but the Rapid River fish is twice the age of the Pahsimeroi fish. What a difference the stream makes!
