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Determination of Physical and Hydraulic Preference of Brown & Brook Trout in the Selection of Spawning Locations


During the fall of 1975, 121 brown and 54 brook trout redds were located and intensively studied in seven stream sections of southeastern Wyoming. Depth, mean velocity, and point velocity were measured at the upper edge, pit, and tailspill of each redd. A representative substrate sample was collected from the tailspill and later analyzed using a series of nine sieves. Permeability of the substrate was measured at the redd site using a Mark VI standpipe. The distance to the nearest usable cover was also measured for each redd.

Spawning criteria were then developed for brown and brook trout using the middle 80 percent of the upper-edge mean velocity measurements, the upper-edge depth which 90 percent of the measurements were greater than or equal to, and the substrate size interval comprising 70 percent of the total weight. For brook trout these criteria were determined to be; velocity, 0.12-1.11 fps; depth, > 0.2 ft; substrate size, 0.132-1.99 in. For brown trout: velocity, 0.45-1.50 fps; depth > 0.3 ft; substrate size, 0.25-2.99 in. The criteria can be used to aid in determining suitable spawning flows for Wyoming's smaller streams.

An egg-planting experiment was conducted to attempt to determine the combination of parameters affording the highest percentage survival of brown trout eggs.

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