Out of Place Predators: Using Bioenergetic Efficiency to Explain Predator Performance Across an Array of Small Impoundments in Northeast Utah

Evaluating and understanding preexisting conditions of aquatic systems is essential to develop and implement efficient fisheries management strategies.  In lentic systems, knowledge of basic limnology, morphometry, and fish community composition provides a baseline for management.  The northern region of the Ute Indian Tribe’s Uintah and Ouray Reservation in northeast Utah contains seven rarely studied ponds and reservoirs that support a variety of sport fisheries, but for which little baseline information is known.  We created bathymetric maps and used standard limnological methods to examine temperature, dissolved oxygen, and other key abiotic variables.  We sampled fish communities with gill nets in the littoral zone.  Area and volume of the waters varied greatly from <1 to 172 ha and 1.4x10⁴ to 1.2x10⁷ m³, respectively.  Limnology and fish communities were also highly variable; mid-summer secchi depths ranged among waters from 0.8 to 5.5m while chlorophyll-a concentrations increased as much as 30-fold in one month.  Cold water fish communities were depauperate including primarily rainbow trout (Oncorhynchus mykiss) and/or brown trout (Salmo trutta), and these systems appear to be forage limited.  Warm-water communities included largemouth bass (Micropterus salmoides) and walleye (Sander vitreus) with several cold-water species mixed in as well.  All waters have been stocked annually with a variety of fish species but with little understanding of the biotic or abiotic conditions that limit fish growth and performance.  To further examine the fish communities, specifically limitations to predator performance, we used a bioenergetics approach and quantified bioenergetic efficiency. We observed three primary categories of results for the fishes of these waters: 1) warm-water species in warm-water impoundments exhibit sufficient consumption rates to maintain high-quality body condition 2) cold-water species in warm-water systems experience limited growth and poor condition due to warm temperatures and high respiration rates, and 3) cold-water species in cool to cold water impoundments are inhibited by quality and abundance of prey given the marginal temperatures.  We confirmed these results with dietary and isotopic analyses. Our findings will assist the Ute Tribe Fish and Wildlife Department in establishing an improved sampling protocol, a more cost- and biologically efficient stocking program, and a better overall understanding of the waters on the Reservation.  In addition, ongoing efforts that include field manipulations and foraging modeling will test parallel hypotheses of predator-prey interactions and growth limitation.