Comment on “Assessing the potential for Smallmouth Bass population establishment in Grand Canyon”
No abstract available.
Arizona, Utah↗
Geology topics
Kevin R. Bestgen
Publications and source records attributed to Kevin R. Bestgen.
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↗
Estimating drivers and identifying uncertainties in smallmouth bass population dynamics in an invaded river network
Smallmouth bass ( Micropterus dolomieu ) is an important recreational sportfish and destructive non-native species when introduced into freshwater habitats. There is therefore a need to understand the drivers of, and uncertainties in, smallmouth bass population dynamics for various management objectives. We combined long-term smallmouth bass catch-effort and early life history data from a non-native population in the Green River sub-basin of the upper Colorado River to develop a demographic model that links interannual variability in environmental conditions to recruitment in three river reaches. We used the model to quantify how hydrology, river temperature, and exploitation drive smallmouth bass population dynamics. Early life stages were influenced by timing of hatching and discharge. Dispersal of age-0 fish and density-dependent dynamics were identified as primary sources of uncertainty. Determining the true nature of density-dependent dynamics is important, as the impact of exploitation-based management actions is dependent on the strengths of any density-dependent feedbacks. Our model provides a framework to predict smallmouth bass population responses to future climate conditions, reservoir operations, and exploitation levels.
Utah↗
Assessment of potential recovery viability for Colorado Pikeminnow Ptychocheilus lucius in the Colorado River in Grand Canyon
Colorado Pikeminnow Ptychocheilus lucius, the Colorado River’s top native predatory fish, was historically distributed from the Gulf of California delta to the upper reaches of the Green, Colorado, and San Juan rivers in the Colorado River basin in the Southwestern US. In recent decades Colorado Pikeminnow population abundance has declined, primarily due to predation by warmwater nonnative fish and habitat modification following dam construction. Small, reproducing populations remain in the Green and upper Colorado rivers, but their current population trajectory is declining and the San Juan River population is maintained primarily through stocking. As such, establishment of an additional population could aid recovery efforts and increase the species’ resilience and population redundancy. The Colorado River in Grand Canyon once supported Colorado Pikeminnow, but until recently habitat suitability in this altered reach was considered low due to a depressed thermal regime and abundant nonnative predators. Climate change and ongoing drought has presented an opportunity to evaluate the feasibility of native fish restoration in a system where declining reservoir storage has led to warmer releases and re-emergence of riverine habitat. These changes in the physical attributes of the river have occurred in concert with a system-wide decline in nonnative predators. Conditions ten years ago were not compatible with reintroduction feasibility in Grand Canyon; however, due to rapidly changing conditions an expert Science Panel was convened to evaluate whether the physical and biological attributes of this reach could now support various life stages of Colorado Pikeminnow. Here, we report on the evaluation process and outcome from the Science Panel, which developed a science-based recommendation to the U.S. Fish and Wildlife Service on reintroduction feasibility. The Science Panel concluded that current habitat attributes in Grand Canyon could satisfy some, but perhaps not all, Colorado Pikeminnow life history requirements. This reach has the potential to support adult and sub-adult growth, foraging, migrations, and spawning, but low juvenile survival may limit recruitment. However, populations of other native species are successfully reproducing and increasing in western Grand Canyon, even in areas once considered suboptimal habitat. Should managers decide to move to the next phase of this process, actions such as experimental stocking and monitoring, telemetry studies, bioenergetics modeling, and laboratory-based research may provide additional information to further evaluate a potential reintroduction effort in this rapidly changing but highly altered system.
Arizona↗
Toward improved prediction of streamflow effects on freshwater fishes
Understanding the effects of hydrology on fish populations is essential to managing for native fish conservation. However, despite decades of research illustrating streamflow influences on fish habitat, reproduction and survival, biologists remain challenged when tasked with predicting how fish populations will respond to changes in flow regimes. This uncertainty stems from insufficient understanding of the context-dependent mechanisms underlying fish responses to, for example, periods of reduced flow or altered frequency of high-flow events. We aim to address this gap by drawing on previous research to hypothesize mechanisms by which low- and high-flows influence fish populations and communities, identifying challenges that stem from data limitations and ecological complexity, and outlining research directions that can advance an empirical basis for prediction. Focusing flow-ecology research on testing and refining mechanistic hypotheses can help narrow management uncertainties and better support species conservation in changing flow regimes.
Fisheries Magazine↗
Water storage decisions will determine the distribution and persistence of imperiled river fishes
Managing the world’s freshwater supply to meet societal and environmental needs in a changing climate is one of the biggest challenges for the 21 st century. Dams provide water security, however, the allocation of dwindling water supply among reservoirs could exacerbate or ameliorate the effects of climate change on aquatic communities. Here, we show that the relative sensitivity of river thermal regimes to direct impacts of climate change and societal decisions concerning water storage vary substantially throughout a river basin. In the absence of interspecific interactions, future Colorado River temperatures would appear to benefit both endemic and nonnative fish species. However, endemic species are already declining or extirpated in locations where their ranges overlap with warmwater nonnatives and changes in water storage may lead to warming in some of the coolest portions of the river basin, facilitating further nonnative expansion. Integrating environmental considerations into ongoing water storage negotiations may lead to better resource outcomes than mitigating nonnative species impacts after the fact.
Ecological Applications↗
Designing flows to enhance ecosystem functioning in heavily altered rivers
More than a century of dam construction and water development in the western United States has led to extensive ecological alteration of rivers. Growing interest in improving river function is compelling practitioners to consider ecological restoration when managing dams and water extraction. We developed an Ecological Response Model (ERM) for the Cache la Poudre River, northern Colorado, USA, to illuminate effects of current and possible future water management and climate change. We used empirical data and modeled interactions among multiple ecosystem components to capture system-wide insights not possible with the unintegrated models commonly used in environmental assessments. The ERM results showed additional flow regime modification would further alter the structure and function of Poudre River aquatic and riparian ecosystems due to multiple and interacting stressors. Model predictions illustrated that specific peak flow magnitudes in spring and early summer are critical for substrate mobilization, dynamic channel morphology, and overbank flows, with strong subsequent effects on instream and riparian biota that varied seasonally and spatially, allowing exploration of nuanced management scenarios. Instream biological indicators benefitted from higher and more stable base flows and high peak flows, but stable base flows with low peak flows were only half as effective to increase indicators. Improving base flows while reducing peak flows, as currently proposed for the Cache la Poudre River, would further reduce ecosystem function. Modeling showed that even presently depleted annual flow volumes can achieve substantially different ecological outcomes in designed flow scenarios, while still supporting social demands. Model predictions demonstrated that implementing designed flows in a natural pattern, with attention to base and peak flows, may be needed to preserve or improve ecosystem function of the Poudre River. Improved regulatory policies would include preservation of ecosystem-level, flow-related processes and adaptive management when water development projects are considered.
Colorado↗
Temperature–not flow–predicts native fish reproduction with Implications for climate change
Habitat alterations and introduction of nonnative fishes reduced the distributions of the Flannelmouth Sucker Catostomus latipinnis , Bluehead Sucker C. discobolus , and Roundtail Chub Gila robusta to less than 50% of their historical ranges. Climate change models generally predict decreased streamflows and increased water temperatures that may further affect these species. Understanding the effects of flow and water temperature on their life histories should lead to better assessments of climate change impacts on extant populations and more informed management for species conservation. Basinwide larval fish sampling and hatch dates derived from otolith daily increment counts showed that water temperature was the dominant environmental factor cueing reproduction in the upper White River basin, Colorado. Reproduction for all three species began in spring, occurring first at warmer, lower-elevation, downstream locations and progressing upriver to higher elevations as water temperatures increased. Warmer water temperatures in tributaries initiated earlier reproductive activity compared to adjacent cooler main-stem habitat. Presence of larvae in samples and estimated hatch dates demonstrated a distinct, predictable upstream progression of reproduction associated with warming water and clear upstream limits to reproduction for all three species. Larval presence and hatching dates revealed earlier reproductive activity in 2012 than in 2013, driven by lower flow and earlier stream warming. A regression model predicted stream temperature during fish spawning seasons under different climate change scenarios and showed expanded upstream limits of thermally suitable reproductive habitat and earlier reproduction for our study species. The long-term implications of climate change are unknown, but managers should strive to perpetuate the valuable and relatively pristine native fish community in the upper White River drainage as a vestige of those that formerly existed throughout the Colorado River basin.
Colorado↗
Tributary use by imperiled Flannelmouth and Bluehead Suckers in the upper Colorado River Basin
Habitat alterations and establishment of nonnative fishes have reduced the distributions of Flannelmouth Sucker Catostomus latipinnis and Bluehead Sucker C. discobolus to less than 50% of their historical ranges in the Colorado River basin. Tributaries are sometimes less altered than main-stem habitat in the basin and may be important to support various life history processes, but their role in the maintenance of Flannelmouth Sucker and Bluehead Sucker populations is poorly understood. Using mark–recapture techniques, we show tributaries are important habitat for native suckers in the upper Colorado River basin and report three main findings. First, both Flannelmouth and Bluehead suckers likely respond to a thermal cue that initiates spawning movement patterns. Suckers moved into Coal Creek from the White River beginning in mid-May of 2012 and 2013 to spawn. The majority of sucker spawning movements occurred when water temperatures in White River exceeded 11–14°C and those in Coal Creek were 2.5–4°C warmer, while flows varied between years. Second, based on PIT tag detection arrays, 13–45% of suckers showed spawning site fidelity. Sampling only with fyke nets would have resulted in the conclusion that site fidelity by native suckers was only 1–17%, because nets were less efficient at detecting marked fish. Third, most suckers of both species emigrated from Coal Creek within 48 h after being captured while suckers that were detected only via arrays remained resident for 10–12 d. The posthandling flight response we observed was not anticipated and to our knowledge has not been previously reported for these species. Remote PIT tag antenna arrays allowed for a stronger inference regarding movement and tributary use by these species than what could be achieved using just fyke nets. Tributaries are an important part of Flannelmouth Sucker and Bluehead Sucker life history and thus important to conservation strategies for these species.
Colorado↗
Conservation of native Pacific trout diversity in western North America
Pacific trout Oncorhynchus spp. in western North America are strongly valued in ecological, socioeconomic, and cultural views, and have been the subject of substantial research and conservation efforts. Despite this, the understanding of their evolutionary histories, overall diversity, and challenges to their conservation is incomplete. We review the state of knowledge on these important issues, focusing on Pacific trout in the genus Oncorhynchus. Although most research on salmonid fishes emphasizes Pacific salmon, we focus on Pacific trout because they share a common evolutionary history, and many taxa in western North America have not been formally described, particularly in the southern extent of their ranges. Research in recent decades has led to the revision of many hypotheses concerning the origin and diversification of Pacific trout throughout their range. Although there has been significant success at addressing past threats to Pacific trout, contemporary and future threats represented by nonnative species, land and water use activities, and climate change pose challenges and uncertainties. Ultimately, conservation of Pacific trout depends on how well these issues are understood and addressed, and on solutions that allow these species to coexist with a growing scope of human influences.
Fisheries↗
Population dynamics modeling of introduced smallmouth bass in the upper Colorado River basin
The purpose of these analyses was to identify an effective control strategy to further reduce smallmouth bass in the upper Colorado River basin from the current level. Our simulation results showed that “the surge”, an early to mid-summer increase in electrofishing effort targeting nest-guarding male smallmouth bass, should be made a core component of any future smallmouth bass management strategy in the upper basin. Immigration from off channel reservoirs is supporting smallmouth bass popualtions in the Yampa River and our modeling analyses suggest that smallmouth bass in Little Yampa Canyon might go extinct in a few years under the present level of exploitation.
Colorado, Utah, Wyoming↗
An ecological response model for the Cache la Poudre River through Fort Collins
The Poudre River Ecological Response Model (ERM) is a collaborative effort initiated by the City of Fort Collins and a team of nine river scientists to provide the City with a tool to improve its understanding of the past, present, and likely future conditions of the Cache la Poudre River ecosystem. The overall ecosystem condition is described through the measurement of key ecological indicators such as shape and character of the stream channel and banks, streamside plant communities and floodplain wetlands, aquatic vegetation and insects, and fishes, both coolwater trout and warmwater native species. The 13- mile-long study area of the Poudre River flows through Fort Collins, Colorado, and is located in an ecological transition zone between the upstream, cold-water, steep-gradient system in the Front Range of the Southern Rocky Mountains and the downstream, warm-water, low-gradient reach in the Colorado high plains. The City wanted to better understand the ecological response of the Poudre River ecosystem to potential changes in stream flow and other physical parameters through the conceptual framework of a multivariable integrated model. This goal was met through the use of a probabilistic model based on Bayesian concepts. This construct allowed the integration of a wide range of data and expert opinion (as informed by local data) to predict potential changes to ecosystem conditions under various flow scenarios. Nine flow scenarios representing past, present, and possible future hydrology were developed as the primary model input. Both reach-scale drivers such as stream channel conditions and pollutant loads, as well as ecological conditions, including species composition, interactions, and habitat requirements influenced model-predicted ecosystem outcomes. Model output consisted of probability distributions for eight ecological indicators collectively representing the physical setting, aquatic life, and riparian habitats of the river ecosystem. We are confident in model predictions related to probable trends, relative magnitude of changes and potential ecosystem responses to changing flow conditions, though data availability and the process of converting diverse data types into a common unit (probabilities) limit precision of individual results. Key findings suggest that: The present ecological function of the Poudre River is altered as a result of more than 150 years of human influences that include highly managed flows, urbanization, gravel mining, channelization and urban and industrial encroachment in the floodplain, underscoring the vulnerable and complex character of the Poudre River; A continuation of today’s flow management will lead to ongoing changes in ecosystem condition, and additional water depletions will compromise ecological conditions; High flows play an essential role in maintaining and improving the aquatic and riparian condition of the river; Adequate flows in base-flow periods are critical to desirable water quality, and thriving fish and insect populations; Improvement of native aquatic life is possible if issues related to channel modifications, siltation, invasive species, and base and high flow conditions are managed properly; The present confined river channel and modified flows has reduced the potential for a keystone and iconic species, plains cottonwood, to be self-sustaining in the study area; The streamside corridor retains the potential to support a functioning riparian forest that provides important ecological services if periodic floodplain inundation occurs. Environmental flows that combine stable and adequate flows in base-flow periods with occasional rejuvenating high flows that meet target levels defined in this study are likely improve all biological indicators across the system. ERM test scenarios that include both stable base flows and rejuvenating high flows indicate that substantial improvements in the river ecosystem can be achieved with improved management of flow volumes similar to those observed in the river during the last half century of intensive water development. These results underscore the possibility of improving the river ecosystem through active management while still maintaining the Poudre’s diverse economic benefits and role as a working river. The ERM was designed to represent the multi-dimensional ecological character of the contemporary urban Poudre River. It provides a scientific foundation that can serve as a decision support tool and foster a more informed community discussion about the future of the river as it provides a better understanding of the likely response of the Poudre River ecosystem to environmental flow management and other stewardship activities. In particular, model results can assist managers in developing specific management actions to achieve desirable goals for key indicators of river health.
Colorado↗
Population trends of smallmouth bass in the upper Colorado River basin with an evaluation of removal effects
Smallmouth bass Micropterus dolomieu were rare in the upper Colorado River basin until the early 1990’s when their abundance dramatically increased in the Yampa River sub-basin. Increased abundance was due primarily to colonization from Elkhead Reservoir, which was rapidly drawn down twice, first to make improvements to the dam (1992) and a second time for reservoir expansion (2005), and allowed escapement of resident bass to the river through an unscreened outlet. Elkhead Reservoir is located on Elkhead Creek, a tributary of the Yampa River. The rapid Elkhead Reservoir drawdown in 1992 was followed by a period of drought years with low, early runoff in the Yampa River sub-basin that benefitted smallmouth bass reproduction. This combination of factors allowed smallmouth bass to establish a self-sustaining population in the Yampa River. Subsequently, successful recruitment allowed smallmouth bass to disperse upstream and downstream in the Yampa River and eventually move into the downstream Green River. Smallmouth bass were also likely introduced, by unknown means, into the upper Colorado River and have since dispersed in this sub-basin. The rapid increase of smallmouth bass in the upper Colorado River basin overlapped with significant reductions in native fish populations in some locations. The threat to these native fishes initiated intensive mechanical removal of smallmouth bass by the Upper Colorado River Endangered Fish Recovery Program. In general, three factors explain fluctuating patterns in smallmouth bass density in the upper Colorado River basin in the last decade: reductions due to electrofishing removal, bass recovery after exploitation due to recruitment and immigration, and changes due to environmental factors not related to electrofishing and other management actions. Our analyses indicated that smallmouth bass densities were substantially reduced in most years by 7 electrofishing removal efforts. Less often, but dramatically in some cases, environmental effects were also responsible for significant declines in smallmouth bass densities in some reaches. Abundant year classes of young smallmouth bass produced in low flow and warm years such as 2007 have potential to overwhelm removal efforts, and the year class persists for one or more years. Nonetheless, it appears that increased electrofishing removal efforts from 2007 to 2011 resulted in sustained reductions in density of smallmouth bass sub-adults and adults throughout the upper basin despite environmental conditions that favored smallmouth bass reproduction in some years (e.g. 2007 and 2009), subsequent recruitment into sub-adult and adult age classes, and movement of smallmouth bass which previously (prior to increases in electrofishing removal efforts) allowed densities to recover in some reaches. We recommend that removal efforts continue in most areas of the upper basin but that the Recovery Program consider allocating effort based on population trends and suspected areas of highest smallmouth bass reproduction. For instance, reproduction, recruitment, and movement of smallmouth bass allowed densities to recover in some reaches, particularly Little Yampa Canyon. Smallmouth bass population recovery implies that areas such as Little Yampa Canyon itself or adjacent reaches (especially upstream), may provide important habitat for age-0 production. We recommend continued assessment of smallmouth bass populations in reaches where reproduction or age-1 nurseries are suspected, such as Little Yampa Canyon and the adjacent upstream reach. It may also be necessary to expand monitoring to areas surrounding suspected sources of smallmouth bass reproduction and increase electrofishing removal effort in these reaches.
Colorado, Utah↗