Lethal and non‐lethal effects of predation by native fish and an invasive crayfish on hatchery‐reared age‐0 lake sturgeon (Acipenser fulvescens Rafinesque, 1817)
2018
Crossman, J. A. | Scribner, K. T. | Forsythe, P. S. | Baker, E. A.
The objective was to investigate the effects of two native fish predators (adult rock bass Ambloplites rupestris, and smallmouth bass Micropterus dolomieue) and an invasive benthic crayfish (Orconectes rusticus) on habitat choice and survival of hatchery‐reared age‐0 lake sturgeon (Acipenser fulvescens). Three length‐classes (mean total length ± 1 SD) of 68.4 ± 12.7 cm, 85.9 ± 15.0, and 111.6 ± 15.4 cm corresponding to 8–9, 11–13, and 15–16 weeks of age, respectively, were examined. Experiments were conducted in a circular (2.44 m diameter, 0.6 m deep) fiberglass tank divided into two equal sections (volume of each section: 2.81 m³). Each section included three contiguous and equal sized substrate types [sand, small gravel (4–10 mm diameter), and cobbles (30–50 mm diameter)] along with the water column providing a choice of habitats. Survival and substrate choice were quantified with and without predators over 24 hr with 30 sturgeon per trial. Multiple trials were repeated for each length‐class and predator type. Survival was also evaluated when alternate prey (emerald shiners Notropis atherinoides) were present in equal numbers (n = 15 per trial). Sturgeon used sand in the absence of a predator or in the presence of fish predators, but in the presence of crayfish the water column (58 ± 5%) was used in increasingly higher proportions by the end of the trial. Survival was significantly lower for sturgeon exposed to crayfish (54%) compared to all other fish predators (97%). Fish predators consumed significantly more alternate prey (32%) than sturgeon (0%) while crayfish consumed significantly more sturgeon (35%) compared to alternate prey (0%). Results demonstrate that non‐lethal effects may contribute to higher rates of mortality between alternate predator types through predator‐induced occupancy of non‐preferred habitats.
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