Evaluation of Wildlife Depredation at Fish Hatcheries in the Intermountain West

• Main Author: Pitt, William C.
• Format: Others
• Published: DigitalCommons@USU 1995
• Subjects: evaluation; wildlife depredation; fish hatcheries; intermountain west; Life Sciences
• Online Access: https://digitalcommons.usu.edu/etd/5311; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=6365&context=etd

During 1993- 1994, I investigated wildlife depredation at Intermountain West fish hatcheries to quantify losses, determined the reliability of bioenergetics models and hatchery manager perceptions to predict losses, and investigated the effectiveness of simple control measures. I observed predators and surveyed managers to quantify the extent of depredation losses and to identify the species responsible. Great blue herons (Ardea herodias), black-crowned night herons (Nycticorax nycticorax), ospreys (Pandion haliaetus), and California gulls (Larus californicus) were the most significant predators of hatchery fish in the field study, and were perceived as such by hatchery managers. Losses to avian predators at two hatcheries were 7.0% and 0.6% of annual production based on my observational data, but hatchery managers believed depredation losses were 15% at each hatchery. I estimated the consumption of rainbow trout (Oncorhynchus mykiss) by great blue herons using bioenergetics models of existence metabolism, existence metabolism plus reproductive costs, and field metabolic rate. compared the model-based predictions to observed consumption rates of free-ranging herons foraging at a fish hatchery. The fish consumption predicted by the existence metabolism model and observed consumption were similar from October- June. During the breeding season, observed consumption was higher than consumption predicted by the existence metabolism model but lower than that expected from the energy requirements for breeding individuals. This result was expected given that only a portion of the bird population was breeding. Although consumption predicted by the field metabolic rate differed significantly from observed consumption for more months than the existence metabolism models, predicted annual consumption from field metabolic rate and observed annual consumption were not signliJcantly different (.E < 0.05). Peak observed consumption occurred during August and September and was predicted by the model. Performance of the three models may be improved with estimates of population structure and more reliable population estimates. I evaluated the effectiveness of perimeter fencing in reducing heron depredation on fish raised in concrete raceways at a trout hatchery in Midway, Utah. Fences were constructed of single-strand monofilament line placed 20 cm above raceway walls. Fences had no impact on the number of birds foraging or their fish consumption rate.