Guidelines for Rearing Substrate Size for Sturgeon Free Embryos and Larvae: Behavioral Response of Kootenai White Sturgeon Early Life Stages to Gravel, Pebble, and Rubble Substrates

Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programs. We conducted experiments in artificial streams to observe the use of rock size by free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus). Most (≥ 90%) free embryos in streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks and few moved downstream. Thus, all three substrates provide cover for most fish. However, in rock-mixture tests, with a variable percent of pebble, small rubble, or large rubble in different tanks, most free embryos stayed hidden in all mixtures, but fish preferred small rock (pebble; P = 0.01). This preference indicates a strong innate preference for small substrate that may be related to greater survival and growth. As free embryos developed into larvae, they left the cover of rocks and dispersed downstream. For free embryos and pre-dispersal larvae, a rock mixture of 10% gravel (16−32 mm diameter) and 30−40% pebble (diameter, 30−60 mm) should provide suitable rearing substrate. The remaining 50−60% should be larger rocks  (mixed rubble and boulders) for spawning and egg attachment and rearing.