Reservoir Food Webs and Predator-Prey Interactions

Led By

Lake and Reservoir Researchers

Study Area

Select reservoirs

Project Status

Ongoing

Research Objectives

• Characterize and quantify interactions among key fish predators and prey in select reservoirs when required for addressing existing or emerging management uncertainties.

Project Description

Understanding how different species interact is central to sport fisheries management. For example, if predation on stocked fish intended for anglers (e.g., rainbow trout) limits development of a recreational fishery, modifying stocking practices (e.g., size of fish or timing) or other actions may be needed to improve the survival of stocked fish.

Alternatively, the recruitment success, growth and survival of sport fish sustained through natural reproduction rather than stocking can depend on numerous factors such as fluctuations in water levels or primary forage fish populations. Understanding relationships among factors helps identify potential management actions for improving sport fish growth and survival when necessary.

Lake and Reservoir Researchers use a suite of sampling methods and analytical tools to characterize reservoir food webs and predator-prey interactions when detailed assessments are needed to address management uncertainties. Sampling methods include various types of nets to catch different life-stages of fish occupying near- and offshore habitats to characterize spatial-temporal interactions among species. Analytical tools such as stable isotopes (chemical composition of fish), bioenergetics models, and population dynamics models are used to map food webs and quantify the influence of different species on others.

Current research involves investigating interactions between rainbow smelt and walleye in Horsetooth Reservoir (northeast Colorado). Rainbow smelt, a small-bodied forage fish, were introduced in 1983 to provide a prey base for walleye and smallmouth bass. The population of smelt can fluctuate dramatically. When highly abundant in the reservoir, growth of sport fish greatly improves, but they also limit natural reproduction by walleye through competition with and/or predation on larval/juvenile walleye. This research aims to identify management strategies for balancing the advantages of smelt with their disadvantages as the primary forage fish in the Horsetooth Reservoir food web.

Associated Publications

Hansen, A.G., J.S. Thompson, L.N. Hargis, D. Brauch, and B.M. Johnson. 2019. Predatory threat of introduced yellow perch in a salmonid dominated reservoir food web. North American Journal of Fisheries Management 39:172-190.

Johnson, B.M., W.M. Pate, and A.G. Hansen. 2017. Energy density and dry matter content in fish: new observations and an evaluation of some empirical models. Transactions of the American Fisheries Society 146:1262-1278.

Johnson, B.M., J.M. Lepak, and B.A. Wolff. 2015. Effects of prey assemblage on mercury bioaccumulation in a piscivorous sport fish. Science of the Total Environment 506-507:330-337.

Lepak, J.M., C.N. Cathcart, and W.L. Stacy. 2014. Tiger muskellunge predation upon stocked sport fish intended for recreational fisheries. Lake and Reservoir Management 30:250-257.

Lepak, J.M., A.G. Hansen, E.T. Cristan, and D. Williams. 2023. Rainbow smelt (Osmerus mordax) influence on walleye (Sander vitreus) recruitment failure: mitochondrial DNA evidence supporting the predation hypothesis. Journal of Fish Biology 103:1543-1548.

Lepak, J.M., A.G. Hansen, B.M. Johnson, K. Battige, E.T. Cristan, C.J. Farrell, W.M. Pate, K.B. Rogers, A.J. Treble, and T.W. Walsworth. In press. Cyclical multi-trophic-level responses to a volatile, introduced forage fish: learning from four decades of food web observation to inform management. Fisheries.

Pate, W.M., B.M. Johnson, J.M. Lepak, and D. Brauch. 2014. Managing for coexistence of kokanee and trophy lake trout in a montane reservoir. North American Journal of Fisheries Management 34:908-922.

Wolff, B.A., B.M. Johnson, and J.M. Lepak. 2017. Changes in sport fish mercury concentrations from food web shifts suggest partial decoupling from mercury loading in two Colorado reservoirs. Archives of Environmental Contamination and Toxicology 72:167-177.

Predation on Stocked Fish fact sheet
Fish Bioenergetics Research fact sheet