Geology topics

Kirk L. Young

Publications and source records attributed to Kirk L. Young.

4 recordsLinked to original sources

USGS2025

Declining reservoir elevations following a two-decade drought increase water temperatures and non-native fish passage facilitating a downstream invasion

River ecosystems are threatened by interactions among river regulation, non-native species, and climate change. Water use has exceeded supply in USA’s Colorado River basin draining its two largest storage reservoirs (Lake Powell and Lake Mead). In 2022, Lake Powell began releasing water from its lower epilimnion into the Grand Canyon segment of the Colorado River, which (1) increased rates of fish passage from the reservoir through the dam and (2) created river temperatures suitable for establishment of non-native fishes. Subsequently, smallmouth bass ( Micropterus dolomieu) reproduced there for the first time. To assist managers concerned about this invasion, we developed models that (1) predicted propagule pressure at different reservoir elevations and (2) linked reservoir storage/operations, water temperatures, and population dynamics to forecast smallmouth bass population growth potential. Maintaining Lake Powell elevations above 1094 m (3590 ft) would likely minimize propagule pressure from the reservoir and create downstream conditions that minimize smallmouth bass population growth. Dam and reservoir management will likely be less effective for managing smallmouth bass if smallmouth bass become abundant in far downstream reaches.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2021

Assessing the population impacts and cost‐effectiveness of a conservation translocation

Managers often move, or translocate, organisms into habitats that are assumed to be suitable, however the consequences of these translocations are usually not rigorously assessed. Robust assessment of these management experiments should consider impacts to both donor and recipient populations and compare the cost‐effectiveness of translocations to other actions. Here we evaluate translocations of a federally listed fish species, humpback chub within a tributary to the Colorado River in its Grand Canyon reach (Arizona, USA). We analyze mark‐recapture data with multistate models to estimate vital rates (growth, survival, and movement) for the donor and recipient populations while accounting for substantial temporal variation in vital rates. We then use stochastic matrix projections to quantify the impact of translocations on adult population size. Lastly, we compare costs of translocations to another, legally required management action, non‐native fish removal, by modifying an existing bioeconomic model. We estimate that six of eight translocations during the study period positively impacted adult abundance and that the overall population impact was positive. Population projections suggest that each chub translocated per year increases the equilibrium adult population size by 1.2 (95% CI: 0.4 – 2.2) adults, lessening the need for non‐native fish removal. Continuation of translocations at the current rate is expected to save managers ~$50,000 per year by decreasing the annual probability of removals from 0.26 to 0.15. Further savings and decreases in removals could be attained by avoiding translocations in years when there has been no winter/spring runoff and modifying the number of translocated individuals based on estimates of juvenile production in the lower LCR. Synthesis and applications . Translocations that increase the abundance of a rare species can sometimes be viewed as a hedge against future declines that might necessitate more costly interventions. Quantifying population benefits and economic costs of management actions like translocations and comparing alternative actions can lead to cost effective conservation that is more easily sustained.

Arizona↗

USGS2018

Brown trout in the Lees Ferry reach of the Colorado River—Evaluation of causal hypotheses and potential interventions

Over the period 2014–2016, the number of nonnative brown trout (Salmo trutta) captured during routine monitoring in the Lees Ferry reach of the Colorado River, downstream of Glen Canyon Dam, began increasing. Management agencies and stakeholders have questioned whether the increase in brown trout in the Lees Ferry reach represents a threat to the endangered humpback chub (Gila cypha), to the rainbow trout (Oncorhynchus mykiss) sport fishery, or to other resources of concern. In this report, we evaluate the evidence for the expansion of brown trout in the Lees Ferry reach, consider a range of causal hypotheses for this expansion, examine the likely efficacy of several potential management interventions to reduce brown trout, and analyze the effects of those interventions on other resources of concern. The brown trout population at Lees Ferry historically consisted of a small number of large fish supported by low levels of immigration from downstream reaches. This population is now showing signs of sustained successful reproduction and is on the cusp of recruiting locally hatched fish into the spawning class, based on analysis with a new integrated population model. The proximate causes of this change in status are a large pulse of immigration in the fall of 2014 and higher reproductive rates in 2015–2017. The ultimate causes of this change are not clear. The pulse of immigrants from downstream reaches in fall 2014 may have been induced by three sequential high-flow releases from the dam in November of 2012–2014, but may also have been the result of a unique set of circumstances unrelated to dam operations. The increase in reproduction may have been the result of any number of changes, including an Allee effect, warmer water temperatures, a decrease in competition from rainbow trout, or fall high-flow releases. Correlations over space and time among predictor variables do not allow us to make a clear inference about the cause of the changes. Under a null causal model, and without any changes to management, we predict there is a 36-percent chance the brown trout population at Lees Ferry will not show sustained growth, and will remain around a mean size of 5,800 adults, near its current size; in contrast, we predict there is a 64-percent chance that the population has a positive intrinsic growth rate and will increase 3–10 fold over the next 20 years. A humpback chub population model linked to the brown trout model suggests an increase of brown trout of this magnitude could lead to declines in the minimum adult humpback chub population over the same time period. Forecasts of rainbow trout abundance, however, suggest that increased abundance of brown trout in the Lees Ferry reach does not pose a threat to the rainbow trout fishery there. There are interventions that may be effective in moderating the growth of the brown trout population in the Lees Ferry reach of the Colorado River. Across causal hypotheses, we predict that removal strategies (for example, a concerted electrofishing effort or an incentivized take program targeted at large brown trout) could reduce brown trout abundance by approximately 50 percent relative to status quo management. Reductions in the frequency or a change in the seasonal timing of high-flow releases from Glen Canyon Dam could be even more effective, but only under the causal hypotheses that involve effects of such releases on immigration or reproduction. Brown trout management flows— dam releases designed to strand young fish at a vulnerable stage—may be able to reduce brown trout abundance to some degree, but are not forecast to be the most effective strategy under any causal hypothesis. We predict that the alternative management interventions would have effects on other resource goals as well, and the pattern of these effects differs across causal hypotheses. The removal strategies would incur direct costs (on the order of $7 million over 20 years) and the mechanical removal strategy is unethical from the perspective of several tribes. The strategies that involve reducing the frequency of high-flow releases from Glen Canyon Dam would decrease the ability to transport and store sediment in the ecosystem, potentially undermining goals associated with sandbar building, recreation, and riparian vegetation, but would increase hydropower revenue. Trout management flows would reduce hydropower revenue. From the standpoint of humpback chub, the alternative strategies largely follow the effect on brown trout; when brown trout abundance is reduced, predation pressure decreases, and humpback chub viability is predicted to increase, but the variation in predicted chub viability is not large across strategies or causal hypotheses. To design a response to brown trout, management agencies will need to navigate both the tradeoffs among resources goals and the uncertainty in the causes of the brown trout expansion. Continued monitoring, possibly coupled with new research or experimental management actions that better inform demographic and ecological dynamics, can help to reduce the causal uncertainty.

Arizona↗

USGS2017

Population expansion of Humpback chub in western Grand Canyon and hypothesized mechanisms

Humpback chub, Gila cypha , is an endangered warm water fish endemic to the Colorado River basin of southwestern North America. In Grand Canyon National Park, cold hypolimnetic water-release temperatures from Glen Canyon Dam have largely precluded successful spawning and recruitment of humpback chub in the mainstem Colorado River. Therefore, the species has utilized the warmer, more saline, and free-flowing Little Colorado River for its primary spawning habitat and continued existence. Based on long-term fish sampling efforts, we document local recruitment and population expansion of humpback chub in the western Grand Canyon and hypothesize that this is a result of recent warmer mainstem water temperatures. Continued recruitment and population expansion of humpback chub in the western Grand Canyon could potentially reduce extinction risk by providing population redundancy and less reliance upon the Little Colorado River for the species survival in the Grand Canyon.

Arizona↗