Laurentian Great Lakes steelhead are a complex stock of fish. The population is a mixture of hatchery-released and wild, naturally reproduced fish originating from many different streams. Knowing the natal streams of the fish is important to best managing this species, as it allows for targeted insertion and management to the areas that are the major contributors to the total lake population. Fortunately, we may be able to determine the natal stream of a fish by looking at its otolith.

Otoliths are the ear bones of a fish. They are commonly referred to as "lucky stones." As early as the egg stage, a fish begins to form the largest of the three parts of the otoliths, called sagittae. The two smaller pairs of otoliths form near the time of hatching and are called the papilla and asterisci. Fish accumulate material on their otoliths daily and also exhibit yearly growth patterns, similar to the pattern seen in tree rings.

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Photo by Nicole Watson