561 items found
Post-Stocking Performance of Triploid Walleye
Led By
Lake and Reservoir Researchers and Colorado State University (CSU)
Study Area
Select reservoirs
Project Status
Ongoing
Research Objectives
- Measure the post-stocking feeding, growth and survival of sterile walleye relative to their non-sterile counterparts.
- Determine the most appropriate stocking procedures for sterile walleye.
- Evaluate the potential for sterile walleye to interfere with unwanted natural reproduction.
Project Description
Every spring CPW collects eggs from wild populations of walleye to raise in the hatchery and stock back out into reservoirs to supplement fisheries. Some of these eggs are specially treated to produce “triploids”. Triploidy is induced by placing fertilized eggs into a hydrostatic pressure chamber. As a result, the fry that hatch retain an extra set of chromosomes (unlike their normal “diploid” counterparts), rendering them incapable of naturally-reproducing over their lifespan. Because triploid walleye are sterile, they can be stocked to support sport fisheries in strategic locations where natural walleye reproduction is not wanted.
Interest in triploid walleye as a management tool is increasing. However, little is known about their post-stocking performance. Understanding post-stocking performance helps identify best stocking practices and calibrate expectations on potential fishery quality. CPW researchers along with collaborators from CSU have been examining numerous aspects of triploid walleye ecology, including how well they grow and survive after being stocked, the types of prey they eat, their uptake of contaminants like mercury, and potential to interfere with unwanted natural reproduction.
General findings to date indicate that triploids eat and grow similarly to diploids, but do not survive as well early in life, which could potentially be overcome by stocking larger fingerlings rather than fry. Both triploid males and females of mature age exhibited negligible development of reproductive tissues. This was expected for females, but not males, suggesting that the ability of triploid males to interfere with unwanted natural reproduction may be relatively low. However, limited development of reproductive tissues contributed to lower mercury levels in triploid fish compared to diploids, making them safer to eat. Research on triploid walleye is ongoing, but they represent a promising management tool for providing desirable sport fisheries in sensitive locations where natural reproduction is not wanted for purposes of native fish protection or other management objectives.
Associated Publications
Farrell, C.J., A.G. Hansen, M.M. Brandt, C.M. Myrick, B.M. Johnson. 2024. An evaluation of the relative size, condition, and apparent survival of triploid walleye in the wild. North American Journal of Fisheries Management 44:172-188.
Farrell, C.J., B.M. Johnson, A.G. Hansen, and C.M. Myrick. 2022. Induced triploidy reduces mercury bioaccumulation in a piscivorous fish. Canadian Journal of Fisheries and Aquatic Sciences 79:202-212 (Received Editor’s Choice Award).
Farrell, C.J., B.M. Johnson, A.G. Hansen, C.A. Myrick, E.C. Anderson, T.A. Delomas, A.D. Schreier, and J.P. Van Enennaam. 2022. Cytological and molecular approaches for ploidy determination: results from a wild walleye population. North American Journal of Fisheries Management 42:849-856.
Farrell, C.J., B.M. Johnson, A.G. Hansen, B. Avila, and C.M. Myrick. In revision. Does reproduction cause growth deceleration? Induced sterility illuminates the effects of reproduction of growth. Canadian Journal of Fisheries and Aquatic Sciences.
Hansen, A.G., C.J. Farrell, and B.M. Johnson. 2023. Simulated effects of imperfect sterile sport fish stocking on persistence of fertile fish in new exploited populations. North American Journal of Fisheries Management 43:908-934.
[show more]GPS radio telemetry
Resource selection function (RSF)
Spatial point process
Species distribution model
Use–availability data
Wildlife
GPS radio telemetry
Resource selection function (RSF)
Spatial point process
Species distribution model
Use–availability data
Wildlife
Disturbance ecology
Energy development
Habitat fragmentation
Mule deer
Predation risk
Resource selection
Disturbance ecology
Energy development
Habitat fragmentation
Mule deer
Predation risk
Resource selection
Purpose
Human-mediated landscape changes alter habitat configuration, which strongly structures animal distributions and interspecific interactions. The effects of anthropogenic disturbance on predator–prey relationships are fundamental to ecology, yet less well understood. We determined where predation events occurred for fawn and adult female mule deer from 2008 to 2014 in critical winter range with extensive energy development. We investigated the relationship between predation sites, energy infrastructure, and natural landscape features across contiguous areas experiencing different degrees of energy extraction during periods of high and low intensity development.
Methods
We contrast spatial correlates of 286 mortality locations with random landscape locations and mule deer distribution estimated from 350,000 GPS locations. We estimated predation risk with resource selection functions and latent selection difference functions.
Results
Relative to the distribution of mule deer, predation risk was lower closer to pipelines and well pads, but higher closer to roads. Predation sites occurred more than expected relative to availability and deer distribution in deeper snow and non-forested habitats. Anthropogenic features had a greater influence on predation sites during the period of low activity than high activity, and natural landscape characteristics had weaker effects relative to anthropogenic features throughout the study. Though canids accounted for the majority of predation events, felids exhibited stronger landscape associations, driving the observed spatial patterns in predation risk to mule deer.
Conclusions
The emergence of varied interactions between predation and landscape features across contexts and years highlights the complexity of interspecific interactions in highly modified landscapes.
[show more]<em>Oncorhynchus clarkii virginalis</em>
Bayesian network model
<em>Oncorhynchus clarkii virginalis</em>
Bayesian network model
Led By
Study Area
Wild trout streams and stocked sport fisheries across Colorado
Project Status
Complete
Research Objectives
- Investigate the distribution and prevalence of Renibacterium salmoninarum, the causative agent of Bacterial Kidney Disease in Colorado’s wild trout and stocked sport fisheries
Project Description
Native and sport fish populations across Colorado are impacted by many factors including habitat alterations associated with changes in stream flows, temperature, and water quality, and host of less obvious biological threats from diseases and parasites. While the prevalence of many fish diseases has declined in recent years due to good management practices, cases of bacterial kidney disease (BKD) seem to be increasing. The causative agent of bacterial kidney disease is Renibacterium salmoninarum, a gram-positive intracellular parasite. The disease is characterized by the presence of gray-white necrotic abscesses in the kidney and can cause mortality in both wild and cultured salmonids. Unlike other common fish pathogens, this bacterium can be transmitted horizontally between fish through contaminated water and vertically from adult to egg. This likely plays a major role in the persistence of this bacterium in susceptible fish populations.
After going undetected in Colorado hatcheries for 18 years, Renibacterium salmoninarum has been found at four state hatcheries, one federal hatchery, and one wild broodstock lake since 2015. The objective of this study was to document the distribution and prevalence of R. salmoninarum in Colorado’s wild and stocked sport fisheries and investigate if fish stocking practices have influenced that distribution. To accomplish that, second to fifth order wild trout streams were randomly selected in each major river basin and total of 68 streams were sampled. To investigate if stocking practices have affected the distribution of R. salmoninarum, waters stocked by hatcheries with recent positive tests for were matched with nearby waters with similar management and a total of 75 different stocked sport fisheries were sampled. Kidney samples were collected from up to 60 fish from all waters and samples were tested by ELISA, real-time PCR, nested PCR, and DFAT according to standard methods.
Results indicate that the prevalence of R. salmoninarum is high in both wild trout and stocked waters by ELISA but bacteria levels are generally low and not commonly detected by standard DFAT assays. Eighty-seven percent of cases that tested positive by ELISA were below detection levels of DFAT. Only two cases of clinical disease were observed, one wild trout stream and one stocked lake. Ninety-three percent of all waters had some fish that tested positive by ELISA, 12% tested positive by both qPCR and nPCR and 13% tested positive by DFAT. All wild trout waters had some fish test positive by ELISA but there was no difference in the average R. salmoninarum antigen levels of stocked and unstocked waters. There was little evidence that stocking practices were more associated with bacteria levels than stream order or lake elevation. Stocked and unstocked waters had similar prevalence and levels of the bacteria and there was not a strong relationship between historical stocking and bacteria levels, except maybe at very high stocking densities in our largest rivers. Renibacterium salmoninarum appears common and widely distributed in Colorado’s wild and stocked trout fisheries but at low levels that rarely cause disease.
Associated Publication
Bacterial Kidney Disease Research Fact Sheet [show more]Aquatic nuisance species
ANS
Aquatic nuisance species
ANS
State Fish Units
State Trust Lands
Walk-In Access Program
State Parks
Ranching for Wildlife
Fact sheet
State Fish Units
State Trust Lands
Walk-In Access Program
State Parks
Ranching for Wildlife
Fact sheet
Cougar
Diet composition
Foraging
Habitat use
Mortality risk
Mountain lion
<em>Puma concolor</em>
Stable isotope analysis
Urbanization
Cougar
Diet composition
Foraging
Habitat use
Mortality risk
Mountain lion
<em>Puma concolor</em>
Stable isotope analysis
Urbanization
Summary
- Large carnivores, though globally threatened, are increasingly using developed landscapes. However, most of our knowledge of their ecology is derived from studies in wildland systems; thus, for effective conservation and management, there is a need to understand their behavioural plasticity and risk of mortality in more developed landscapes.
- We examined cougar Puma concolor foraging ecology and survival in an expanding urban–wildland system in Colorado from 2007 to 2013. For GPS-collared individuals, we related diet (n = 41; isotopic analysis) to age–sex class and fine-scale space use, with regard to levels of habitat development. We also examined how habitat development impacted risk of mortality (n = 49), using hazards models and records of cougar–human conflict.
- Cougars obtained 63–82% of assimilated biomass from native herbivores, and adult females consistently showed higher use of native herbivores than other age–sex classes. Individuals using the most highly developed areas obtained approximately 20% more of their diet from alternative prey (synanthropic wildlife and domestic species) than those in the least developed areas.
- Overall, survival of adult females was higher than adult males. Yet, use of developed areas substantially increased cougar risk of mortality; for every 10% increase in housing density, risk of mortality increased by 6·5%, regardless of sex.
- Synthesis and applications. Cougars showed flexibility in diet, taking advantage of human-associated prey items, but had high rates of mortality, suggesting that human tolerance, rather than adaptability, may be the limiting factor for range expansion by cougar and other large carnivores. Thus, large carnivore conservation will not only depend upon adequate prey resources, but also limiting potential conflict resulting from depredation of synanthropic wildlife and domestic animals.