: Jesse M. Lepak, PhD Jesse.Lepak@state.co.us
The lake and reservoir research laboratory and its staff at Colorado Parks and Wildlife are devoted to understanding and improving fisheries throughout the state. Our focus is on food web structure and how different species assemblages, lake and reservoir characteristics, prey bases and management strategies affect the numbers, growth and condition of sport fish and their interactions with each other. We use a combination of new and long-standing techniques to address issues facing sport fisheries in Colorado. At any one time, the Group is working several different projects simultaneously.
Please view links for more information:
- Mercury contamination in sport fish has been studied extensively in the eastern US for over five decades. More recently, attention has shifted to the West, and the Lake and Reservoir Research Group has a strong focus on mercury contamination in Colorado’s sport fish. The Group is involved in mercury research to protect the health of Colorado’s anglers while maintaining the quality of angling opportunities. Fish represent an excellent source of lean, low-calorie protein, and are part of a healthy diet according to the Colorado Department of Public Health and Environment. To maximize the benefits of consuming fish and reduce the potential risks, the Lake and Reservoir Research Group continues its work on mercury in collaboration with other researchers. For example, the Group is highly involved in an international effort known as the “Western North American Mercury Synthesis”. This synthesis effort (covering the area outlined in white) was initiated by some of world’s leading mercury experts. The role of the Lake and Reservoir Research Group is to characterize and potentially minimize health risks posed by mercury to humans and wildlife that consume sport fish and other fish.
- In Colorado, tiger muskellunge (sterile hybrids of muskellunge and northern pike) are stocked to suppress white sucker populations. White suckers have been shown to compete with salmonid species including popular sport fish such as rainbow trout, an important sport fish in Colorado. Although tiger muskellunge have been shown to consume white suckers, they also have potential to consume trout. We are investigating the degree to which tiger muskellunge select white suckers as prey versus trout.
- Gill lice (Salmincola spp.) are parasitic copepods that target fishes (primarily salmonids). Gill lice have been found to infest cutthroat trout, kokanee salmon, mountain whitefish, rainbow trout, and brown trout among other species. In Colorado specifically, gill lice have been documented on cutthroat trout, kokanee salmon, and rainbow trout. These fishes represent ecologically and economically important salmonid species in Colorado. Native cutthroat trout in particular have been designated as Colorado’s state fish, and pure lineages of cutthroat trout have recently been found to have limited distributions. Mountain whitefish are also a species of concern in Colorado and have experienced recent population declines. Thus, gill lice infestations represent a threat to sustaining native cutthroat trout and mountain whitefish populations in Colorado. Gill lice limit oxygen exchange through gill filaments on which they are attached and negatively affect fish behavior, immune system function, growth, warm water tolerance, and survival. Gill lice have been observed in private and state hatcheries throughout Colorado and many water bodies in the wild. To date, very little research has been conducted on gill lice, and to our knowledge we are the only Group working on this topic in Colorado, and one of only a few in all of western North America. We are determining gill lice distribution in Colorado, and investigating the current and potential consequences of gill lice on native cutthroat trout and mountain whitefish in Colorado, and other fish species that interact with gill lice.
- Understanding lake and reservoir food web structure plays a crucial role in determining how best to manage a sport fishery. In order to inform management decisions, we use a variety of techniques to characterize important aspects of lake and reservoir fisheries. For example, we use otoliths (calcified structures in a fish’s inner ear) that grow like tree rings to verify the age of sport fish and how fast they grow in a variety of reservoirs, under a variety of conditions. Also, we use stable isotope analyses (a technique where we test fish tissue to determine their diet) to evaluate what prey sources are supporting sport fish populations. These data can be used further to conduct modeling simulations and statistical analyses. This information can aid in determining appropriate stocking densities and management actions to maximize the productivity of a given lake or reservoir and produce a healthy fishery were trophy-sized individuals.
- We are in the testing phase of marking fish using oxytetracycline to determine the stocking success of walleye fry versus fingerling plants, and the stocking success of wiper plants under various different circumstances. Oxytetracycline is an antibiotic that fluoresces (a green-yellow color) under ultraviolet light with a specialized wavelength. Fish are submerged in an oxytetracycline solution and then released into the wild. This technique allows us to distinguish between different groups of fish and compare their success after stocking relative to each other.
The data collected with the techniques described above are provided to Colorado Parks and Wildlife Biologists so they can make informed management decisions based on the most current scientific information available. One of the most important goals of the lake and reservoir research laboratory is to provide information that aids in addressing fisheries problems facing Colorado’s lakes and reservoirs. By conducting targeted research using a variety of techniques, we hope to maintain and potentially enhance Colorado fisheries and angling opportunities.
Publications related to these topics include
- Hargis, L.N., Lepak, J.M., Vigil, E.M., and Gunn, C. 2013. Prevalence and intensity of the parasitic copepod (Salmincola californiensis) on kokanee salmon (Oncorhynchus nerka) in a Colorado reservoir. In Press: Southwestern Naturalist.
- Lepak, J.M., Cathcart, C.N., and Hooten, M.B. 2012. Otolith weight as a predictor of age in kokanee salmon (Oncorhynchus nerka) from four Colorado reservoirs. Canadian Journal of Fisheries and Aquatic Sciences. 69(10):1569-1575
- Lepak, J.M., Hooten, M.B., and Johnson, B.M. 2012. The influence of external subsidies on diet, growth and Hg concentrations of freshwater sport fish: implications for fisheries management and the development of fish consumption advisories. Ecotoxicology. 21(7):1878-1888
- Stacy, W.L., and Lepak, J.M. 2012. Relative influence of prey mercury concentration, prey energy density and predator sex on sport fish mercury concentrations. Science of the Total Environment. 437:104-109
- Lepak, J.M., Fetherman, E.R., Pate, W.M., Craft, C.D. and Gardunio, E.I. 2012. An experimental approach to determine esocid prey preference in replicated pond systems. Lake and Reservoir Management. 28:224-231
- Lepak, J.M., Kinzli, K.D., Fetherman, E.R., Pate, W.M., Hansen, A.G., Gardunio, E.I., Cathcart, C.N., Stacy, W.L., Underwood, Z.E., Brandt, M.M., Myrick, C.M., and Johnson, B.M. 2012. Manipulation of growth to reduce sport fish mercury concentrations on a whole-lake scale. Canadian Journal of Fisheries and Aquatic Sciences. 69(1):122-135