551 items found

1. Predators may create healthier prey populations by selectively removing diseased individuals. Predators typically prefer some ages of prey over others, which may, or may not, align with those prey ages that are most likely to be diseased.
2. The interaction of age-specific infection and predation has not been previously explored and likely has sizable effects on disease dynamics. We hypothesize that predator cleansing effects will be greater when the disease and predation occur in the same prey age groups.
3. We examine the predator cleansing effect using a model where both vulnerability to predators and pathogen prevalence vary with age. We tailor this model to chronic wasting disease (CWD) in mule deer and elk populations in the Greater Yellowstone Ecosystem, with empirical data from Yellowstone grey wolves and cougars.
4. Model results suggest that under moderate, yet realistic, predation pressure from cougars and wolves independently, predators may decrease CWD outbreak size substantially and delay the accumulation of symptomatic deer and elk. The magnitude of this effect is driven by the ability of predators to selectively remove late-stage CWD infections that are likely the most responsible for transmission, but this may not be the age class they typically select. Thus, predators that select for infected young adults over uninfected juveniles have a stronger cleansing effect, and these effects are strengthened when transmission rates increase with increasing prey morbidity. There are also trade-offs from a management perspective—that is, increasing predator kill rates can result in opposing forces on prey abundance and CWD prevalence.
5. Our modelling exploration shows that predators have the potential to reduce prevalence in prey populations when prey age and disease severity are considered, yet the strength of this effect is influenced by predators' selection for demography or body condition. Current CWD management focuses on increasing cervid hunting as the primary management tool, and our results suggest predators may also be a useful tool under certain conditions, but not necessarily without additional impacts on host abundance and demography. Protected areas with predator populations will play a large role in informing the debate over predator impacts on disease

Led By

Jesse ​​Lepak​

Study Area

Four Colorado Reservoirs (Blue Mesa, Granby, Shadow Mountain, Williams Fork)

Led By

Matt Kondratieff  and Eric Richer​ 

Study Area

Statewide

Project Status

Ongoing

Research Objectives

• To evaluate the effects of instream barriers on the upstream and downstream migration of Colorado fishes
• To evaluate the effectiveness of natural and engineered barriers for the protection of native cutthroat trout populations
• To develop fish swimming and leaping performance criteria for Colorado fishes
• To develop fish passage and barrier design criteria
• To assist with fish passage and barrier design for new or existing structures​

Project Description

Vertical obstacles in streams and rivers, such as waterfalls, culverts and water-diversion structures, can impact fish by fragmenting populations and reducing migratory ranges. However, these barriers can also protect fish populations from predators, reduce competition for food and limit the possibility for hybridization and disease. Therefore, it is important that fisheries managers identify and evaluate the impact of in-stream structures on fish populations. CPW has initiated several research studies to evaluate the effects of in-stream structures on Colorado fisheries. These projects can be divided into two distinct categories: (1) fish passage projects and (2) fish barrier projects.

The primary goal of fish passage projects is to restore connectivity to fragmented river systems. Culverts, dams and water-diversion structures are commonly found on most rivers in Colorado and often reduce migratory ranges. Trout and other fish species migrate upstream to spawn and downstream to spend the winter. River systems that are fragmented can impair migration and adversely impact fish populations. Fish passage research is focused on evaluating the effectiveness of existing fishways and developing species-specific design criteria to improve connectivity in Colorado rivers. In response to the 2013 flood along the Colorado Front Range, CPW helped organize a Fish Passage Workshop and Webinar to disseminate design options and criteria to improve passage at water-diversion structures. 

Fish barrier projects are primarily focused on protecting native cutthroat trout​​ from downstream threats. Natural or engineered barriers are used to isolate cutthroat trout in headwater streams, which protects them from whirling disease​, hybridization with rainbow trout and competition with brook trout and other non-native fish species. The goal of fish barrier research is to develop design and monitoring guidelines that will improve the selection of natural barriers and effectiveness of engineered barriers. Fish barrier research for cutthroat trout conservation is focused on monitoring existing barriers and applying design criteria to maximize effectiveness of new barrier projects. ​

Associated Publications

Ficke, A.D. and C.A. Myrick. 2007. Fish barriers and small plains fishes: fishway design recommendations and the impact of existing instream structures​. Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado: 109 pp.

Kondratieff, M.C. and C.A. Myrick. 2006. How high can a brook trout jump? A laboratory evaluation of brook trout jumping performance. Transactions of the American Fisheries Society 135: 361-370.

Kondratieff, M.C., and C.A. Myrick. 2005. Two adjustable waterfalls for evaluating fish jumping performance. Transactions of the American Fisheries Society 134:503-508.

Brandt, M.M., P. Holloway, C.A. Myrick, and M.C. Kondratieff. 2005. Effects of waterfall dimensions and light intensity on age-0 brook trout jumping performance. Transactions of the American Fisheries Society 134:496-502.​Myrick, C.A., and M.C. Kondratieff. 2004. An evaluation of a potential barrier to the upstream movement of brook trout in Rocky Mountain National Park, Colorado​. National Park Service Technical Report NPS/NRWRD/NRTR-2005/337.