The distribution, status, & conservation of a narrow endemic, the Inyo Mountains salamander, Batrachoseps campi

Authors: Christopher Norment, Nicholas Gilder, Elizabeth Jockusch

Year: 2023

Abstract

Between 2009 and 2023 we studied the distribution, ecology, and conservation genetics of the Inyo Mountains salamander, Batrachoseps campi (IMS). The IMS is endemic to the Inyo Mountains of California and one of only two extant plethodontid salamanders whose range is restricted to desert ecosystems. Survey efforts during this time resulted in the discovery of 5 new localities, increasing the documented localities to 24. We estimated that in the Inyo Mountains there are ± 15,200 m of IMS riparian habitat, the most common habitat for the species. IMS occurred across an elevation gradient from 523 to 2625 m, mostly ≤ 2 m from surface water. However, we found 9 IMS up to 1100 m from the nearest surface water, suggesting that populations may occur at other high elevation sites without permanent surface water. Riparian habitat supporting salamanders included a diverse mix of woody and herbaceous species. Some geographical variation in coloration occurred, with silver individuals common at 2 northwestern localities and very dark individuals predominating at 3 southern localities; individuals with intermediate amounts of dorsal silver were common elsewhere. Chytrid fungus, Batrachochytrium dendrobatidis, was absent from 36 IMS tested. Genetic relationships among populations of IMS were analyzed using mitochondrial (n = 187 samples) and nuclear (double digest restriction-site associated DNA, n = 93 samples) data. Both datasets show 3 differentiated lineages, with higher genetic structure in the southern part of the range. A surprising amount of connectivity was noted across the main crest of the Inyo Mountains. Long-term drought and intense flash flooding have impacted IMS habitat. Between 2010 and 2023 we observed decreased flow from 10 permanent water sources: 7 (29% of documented localities) support IMS. Although these declines generally appear small, continued drought could put small, localized populations at risk. Flash floods caused by convectional storms damaged riparian habitat in 46% of documented IMS localities, sometimes severely. However, we found little evidence for widespread IMS population decline across the species’ range. Because all documented populations occur in federally-designated wilderness and many are difficult to reach, widespread direct human interference with the species is unlikely, as long as federal and state regulatory authority is maintained. However, climate models generally predict increased frequency and intensity of flash floods, which could further affect IMS habitat and populations. To provide better data for properly managing the IMS a standardized monitoring program should be implemented. 1. The role of calcium carbonate in gross primary production in the Little Colorado River, AZ, & implications for Humpback Chub growth rates – Phoebe Brown*, Eric Moody, Jeffery Muehlbauer, Bridget Deemer, Charles Yackulic, Jessica Corman & Ted Kennedy The lower 13 km of the Little Colorado River (LCR) between the Atomizer Falls complex and the confluence with the mainstem of the Colorado River in Grand Canyon, AZ, is considered key habitat for threatened and endangered native fishes, most notably the Humpback Chub, Gila cypha. While Humpback Chub were historically present only in this lower reach of the LCR, studies of recent translocations above Atomizer Falls have revealed faster growth rates in translocated upper reach individuals. The upper reach differs from the lower reach in that it has reduced calcium carbonate (marl) precipitation rates due to the low pH of groundwater emerging from the springs that feed this reach. Marl precipitation reduces light availability, streambed stability, and availability of phosphorus. These factors can have bottom-up effects on the biomass of benthic invertebrates, which is considerably higher in upper, non-marl reaches. These combined effects may limit primary production in marl reaches in accordance with the differences of fish growth rates observed. Phosphorus availability can impact ecosystems as a limiting nutrient and is known to co-precipitate out of the water column during marl deposition. Thus, we hypothesized that lower bioavailable P in the lower compared to upper reach of the LCR could impact the food base and thus explain lower growth rates of Humpback Chub. An experiment revealed that P addition stimulated increased GPP in both marl and non-marl reaches. These data suggest that while reduced P availability in the lower reach likely contributes to low GPP in the lower LCR, the combined effects of low light availability, streambed instability, and reduced P availability in marl reaches together explain their low primary production. Ultimately, these bottom-up effects may control the growth rates of federally threatened Humpback Chub. 2. Using metabarcoding to survey the biodiversity of intestinal parasites of fishes in Grand Canyon – Isaac Schuman*, Claire Couch, Justin Sanders, Anna Jolles & David Lytle Parasites are undervalued components of a biological community, often grouped within the study of disease ecology in an ecosystem alongside its bacterial and viral pathogens. Outbreaks among host populations or zoonotic spillover are two situations where parasites are obvious. Yet the opposite scenario, where the parasite populations themselves are threatened, can go unnoticed. This project aims to characterize the intestinal parasite communities of three fish species in the Colorado River in Grand Canyon using 18s metabarcoding, as part of an effort to create a modern snapshot of this American landmark’s ecology. Our goal is to describe the broad diversity of parasites in the river, and their geographic and host distributions. The fish host species of interest are native Flannelmouth Sucker, Catostomus latipinnis, Humpback Chub, Gila cypha, and introduced Rainbow Trout, Oncorhynchus mykiss. Understanding the parasite community of Grand Canyon fish species is an important and timely aspect of ecological monitoring. Parasites drive host population dynamics, including through mechanisms such as direct mortality, manipulation of host behavior, and parasite avoidance behavior. Additionally, parasites with complex life cycles rely on multiple hosts at different trophic positions to complete their lifecycles, making them sensitive indicators for functional food chains. Finally, the Grand Canyon aquatic ecosystem is entering an unprecedented state of flux, as drought and water management challenges in the American Southwest reduce Colorado River flow to historic lows. The transition from a cold river defined by dam regulation to a warmer river with an unstable drought-defined flow regime occurs alongside new waves of invasive species and within the global context of climate change. We hypothesize that a longitudinal gradient in parasite diversity will be evident moving downstream within the canyon, as well as areas of increased diversity near the mouths of relatively undisturbed perennial tributaries. Current work from the Lytle lab suggests that aquatic macroinvertebrate diversity is higher in tributaries than in the mainstem Colorado River, and a broad food base for fish will also support a broad variety of parasite life cycles. In contrast, the most ecologically damaged areas of the canyon such as those close to Glen Canyon Dam will show low parasite diversity, with generalist single host parasites making up a larger proportion of that diversity. Feces were sampled from over 120x fish, most commonly C. latipinnis, longitudinally along 450 river-kilometers of the Colorado River in Grand Canyon. DNA was extracted from samples using Qiagen Blood and Tissue kits and sequenced using 18s primers to detect the presence of diverse parasite taxa. We obtained 36.6 million raw 18s reads across 115 fecal samples, with an average of 318,000 reads per sample. Bioinformatic analysis of this sequencing data is currently ongoing, however, presenting the work is still relevant because of the use of novel methods in the system. The information from metabarcoding will complement traditional necropsies by more easily targeting microscopic parasites such as Microsporidia and Apicomplexa. It also allows high volumes of samples to be collected and processed in a minimally invasive manner, an important factor when working with threatened fish in desert rivers. The unique sensitivity of parasites to trophic disturbance, and their permeating effects on ecosystem dynamics, provide a unique and insightful method for assessing the impacts of anthropogenic changes on desert river communities. 3. How beaver pond age affects aquatic invertebrates – Jazmyn Rivera & Susan Washko Beavers are ecological engineers, benefiting the aquatic ecosystems with their dams and ponds. The beaver ponds change over time; beaver ponds of different ages will have different characteristics. These differences will influence what types of aquatic invertebrates will inhabit these ponds. Understanding these different successional stages will help us understand more about the beavers’ role in the ecosystem. We surveyed three newer beaver ponds and four older beaver ponds to assess the aquatic invertebrate community composition and taxa richness. The newer beaver ponds had an average of 18 taxa, whereas the older beaver ponds had an average of 28.25 taxa. The community composition between newer and older ponds was significantly different, due to some species that were unique or abundant for each pond age group. The habitat in the newer ponds is a type of middle ground between wetland and stream habitat. This could mean that few wetland and stream invertebrates can colonize there. The presence of trout in the newer ponds could also contribute to the low number of taxa. Learning more about the biodiversity associated with successional stages of beaver ponds can inform evaluation criteria for restoration using beaver and improve our understanding of beavers’ role in the ecosystem. 4. Lower Colorado River Area Report – Ron Rogers The lower Colorado River Basin encompasses an area that spans from Lee’s Ferry, Arizona, approximately 15 river miles below Glen Canyon Dam (Lake Powell), to the Gulf of California (Sea of Cortez), Mexico. Historically, the dynamic nature of river would have meandered across large flood plains, creating isolated pools, oxbow lakes, and backwater habitats, that were broken in small areas by when not bound by narrow canyons and high gradient reaches. This ecosystem was home to numerous species of fish, reptiles, plants, and invertebrates. However, in less than 100 years, a system of dams, diversions, levees, and canals has left this region as one of the most managed rivers in the world. Many scientists are currently working within the basin to better understand, conserve, and enhance endangered, threatened, and native fish populations. This report highlights some of the research, monitoring, and recovery efforts for fishes within the lower Colorado River Basin. 5. Population genetic structure of the endemic fish Gambusia marshi from the Cuatro Ciénegas basin & its outflow in Coahuila, Mexico – Jia Yan Xie, Kyung Seok Kim, Dylan Powell, Hector Espinosa-Pérez, Eric Moody* & Kevin Roe The valley of Cuatro Ciénegas in Coahuila, Mexico, has the highest degree of local endemism of any habitat in North America. Despite the arid desert climate, the basin harbors an extensive system of permanent streams, wetlands, and spring-fed pools, and is divided into two sub-basins by the central Sierra de San Marcos y Pinos. Microsatellite loci were surveyed to infer the genetic diversity and population structure of Gambusia marshi, a poeciliid fish endemic to the Cuatro Ciénegas basin and the Río Salado de Nadadores in north-east Mexico. Bayesian clustering analysis revealed four genetic populations within G. marshi and a major east–west division corresponding to the Sierra de San Marcos y Pinos. Most sample sites exhibited high levels of genetic differentiation, although there is evidence for recent gene flow between some of these locations. The population of G. marshi in Poza Anteojo is extremely divergent and appears to represent a remnant of a different historical system. The G. marshi in Poza Anteojo should be considered an independent management unit. Documenting the number and distribution of distinct populations of G. marshi provides additional justification for protecting the Cuatro Ciénegas basin from additional water withdrawals and further homogenization via the construction of additional canals. By analyzing the population structure of a widespread species within a region containing many range-restricted and endemic species, these results shed new light on historical connections among aquatic ecosystems and raise awareness of the possibility that units of conservation concern may exist in other, more range-restricted taxa in the Cuatro Ciénegas basin and encourage the assessment of their conservation status. 6. Cross-canyon connections? Conservation genomics of a desert-dwelling lungless salamander (Batrachoseps campi) – Nicholas Van Gilder, Christopher Norment* & Elizabeth Jockusch The Inyo Mountains salamander, Batrachoseps campi, is one of two plethodontid salamanders confined entirely to desert habitat. Though lungless salamanders must stay moist to respire, all known populations of this species occur within the Inyo Mountains of California, an arid range rising between the Owen’s Valley to the west and the Saline Valley to the east. The salamanders occupy discrete areas of riparian habitat in steep-walled canyons separated by mostly inhospitable terrain. Previous genetic work on this species (Yanev and Wake, 1981, Herpetologica 37(1):16-28) suggested that these canyon populations are highly divergent from one another, with limited to no gene flow occurring between sites, and a strong overall north-south separation. Our study examines the population structure and genetic divergence of this species using contemporary molecular approaches and an expanded set of populations. Specifically, 93 samples of B. campi from 17 of 24 known populations were sequenced using a reduced-representation genomic approach (double digest restriction-site associated DNA sequencing, ddRAD), generating thousands of informative markers (single nucleotide polymorphisms, SNPs). Our population assignment analyses indicate the presence of at least three genetic clusters showing detectable admixture across the mountain range, and two of these clusters show connection over the crest of the mountains. Estimated proportions of admixture between clusters decreased with stricter filtering of SNPs, though all filtering approaches support at least three genetic groups. Additionally, we failed to find detectable genetic structure at the finest scale examined, a 425 m stretch of continuous riparian habitat. Measures of Wright’s (1943) fixation index, FST, range from 0.033 to 0.189, with sites in the north generally less differentiated from one another than the sites in the central and southern portion of the range. Overall, measures of differentiation increase with distance between sites, but are generally less than half of the values calculated by Yanev and Wake (1981). With this genomic-scale data, we gain new insight into the connectivity of these canyon populations. While connectivity appears to be the strongest along riparian corridors within canyons, the genetic admixture seen in our results suggests that there has been historical gene flow between populations in sites not connected by obviously mesic habitats. The results of our work offer new perspectives and increased resolution of the evolutionary history and population dynamics of this species of conservation concern. 7. What is the Nevada Cooperative Fish & Wildlife Research Unit? Graduate education, collaborative research, & technical assistance for conservation of Great Basin fish & wildlife – Jeff Falke The Nevada Cooperative Fish and Wildlife Research Unit (NVCFWRU) is part of a nationwide program administered by the U.S. Geological Survey (USGS) that began in 1935. These Units were created to foster college-level research and graduate student training in support of science-based management of fish and wildlife and their habitats. The mission of the Cooperative Research Unit program focuses on developing the conservation workforce of the future through applied graduate education, helping fulfill the training and technical assistance needs of the cooperators, and delivering actionable science to cooperating agencies and organizations. The unique model of the Cooperative Research Unit program increases productivity and capacity by allowing partners to benefit from each other’s strengths, developing better management at every level of fish and wildlife conservation. The Nevada Unit was formed in 2021 via a Cooperative Agreement among the Nevada Department of Wildlife; the University of Nevada, Reno (UNR); the Wildlife Management Institute; the U.S. Fish and Wildlife Service; and USGS. This partnership is the key to the success of the Unit: each of the partners bears part of the cost but receives the whole of the benefit. The benefit comes as products: research published in peer-reviewed journals; students trained as entry-level professionals; and technical assistance provided by recognized experts. Based on the UNR campus, the program will focus on fisheries and wildlife research, ecology, and management, and will promote collaboration among the cooperating agencies. In addition, the program will support a focus on human dimensions and the importance of wildlife conservation to the public’s overall quality of life. Unit scientists are USGS employees with faculty appointments at the host University. They conduct research, advise graduate students, and teach one graduate course annually. Other faculty cooperate in the program by conducting Unit-sponsored research, often carried out through the Research Work Order process, a funding mechanism authorized by Congress specifically for the Cooperative Units. The Great Basin and Nevada are facing unprecedented environmental change. Native plant communities and their associated fish and wildlife species are challenged by invasive weeds, increased fire frequency and intensity, water quantity and quality, and development associated with a growing human population. The new NCFWRU is positioned to complement ongoing work on Great Basin native fish conservation issues, across Nevada and the region, through graduate and post-doctoral research, education, and technical assistance. 8. Long-term monitoring of a native fish in the Muddy River, Nevada – Justin Handtke The Virgin River Chub Gila seminuda persists in the Muddy River despite a complicated conservation status. The species is state listed as Sensitive and of Conservation Priority and is listed as federally endangered in the nearby Virgin River. In the Muddy River in Nevada, long-term monitoring and biannual sampling with hoop nets and minnow traps dating back to 2010 have provided a better understanding of the population dynamics of native fishes in the system. Recurrent monitoring of the fish populations in the Muddy River continues to be of importance following rotenone treatments from 2016-2019 for nonnative fish removal. Despite an apparent decline in Virgin River Chub relative abundance over time, increased CPUE of Virgin River Chub across multiple age-classes, a relatively high mean annual growth rate, and an overall increase in capture frequencies indicate the species may be rebounding in the Muddy River. 9. 2023 update regarding Long Valley Speckled Dace populations – Nicole Hatakeyama* & Nick Buckmaster The speckled dace, Rhinichthys osculus, is a widely distributed temperate freshwater minnow, Cypriniformes, found throughout western North America. The Long Valley speckled dace (LVSD), Rhinichthys nevadensis caldera, is a subspecies of the desert speckled dace, Rhinichthys nevadensis, that historically inhabited streams and marshes within the Long Valley Caldera part of the Upper Owens River drainage. At present however, LVSD are limited to only three known locations: White Mountain Research Center (WMRC), O’Harrell Creek, and Whitmore Marsh. The WMRC is an artificial refuge pond outside of LVSD native range that was established in 2017 and hosts a stable population of over 1,000 fish. In 2022 and 2023, LVSD were translocated from WMRC to O’Harrell Creek to establish a new population of LVSD within their native range. A survey later in 2023 found a few young-of-year LVSD and the creek will continue to be monitored for successful establishment. Lastly, the primary wild population of LVSD exists at Whitmore Marsh, which is an alkali marsh that covers roughly 1 acre and has little open water habitat. Unfortunately, the source spring for the marsh was developed into a public swimming pool and discharges a lightly chlorinated stream adjacent to the source spring. Possibly due to chlorine exposure after the 2016 winter, the relatively stable LVSD population revealed no fish during surveys conducted in 2017, and trapping efforts in 2018, 2021, and 2022 yielded very few numbers. However, in September 2023, trapping efforts yielded over 200 healthy LVSD hopefully indicating successful repopulation of the marsh. 10. Ten years of ecosystem monitoring in the Ash Meadows Fish Conservation Facility refuge tank – Daniel Villanueva*, Olin Feuerbacher, Jennifer Gumm, Ambre Chaudoin, Jeffrey Goldstein, Kevin Wilson & Bryce Donaghue The Ash Meadows Fish Conservation Facility (AMFCF) was constructed in 2013 to support the conservation and recovery of Devils Hole pupfish, Cyprinodon diabolis. The AMFCF houses a 100,000-gallon refuge tank that is a replica of the Devils Hole habitat that duplicates the Devils Hole pupfish natural ecosystem. Ten years of ecosystem monitoring have been conducted in the refuge tank. Monitoring efforts are ongoing with monthly algae surveys, invertebrate surveys, and weekly predaceous diving beetle, Neoclypeodytes cinctellus, trappings to study the health of this artificial ecosystem. Here, we analyze how aspects of the refuge tank community have changed over the years. We examined the percent coverage of algae species found in the shallow shelf of the refuge tank, invertebrate abundance, and population dynamics of N. cinctellus. Spirogyra sp. is a species of algae present in the refuge tank, and it’s important for breeding behavior, egg survival, and larval fish survival. Spirogyra percent coverage has fluctuated over time but has remained present in the refuge tank and responds positively to management actions such as removing detritus and cyanobacteria. Amphipods, Hyallela azteca, are an important invertebrate food source for Devils Hole pupfish. A gut analysis of C. diabolis determined that H. azteca and the Devil’s Hole warm spring riffle beetle, Stenelmis calida calida, combined, averaged 6% of the observed gut contents (Wilson and Blinn, 2007, Western North American Naturalist, 67(2):185 -198). A total of three amphipods was captured during monthly invertebrate surveys in 2020. The following year, a total of 807 amphipods were captured during monthly invertebrate surveys. We hypothesize that the decline in N. cinctellus may have led to an increase in amphipod abundance. Neoclypeodytes cinctellus trapping efforts began in March 2018, and as of August 2023, over 35,000 beetles have been removed from the refuge tank. In 2018, 8,659 beetles were trapped over 186 hours, resulting in a catch per unit effort (CPUE) of 47. In 2023, 14 beetles were trapped over 156 hours, bringing the CPUE to 0.090. The US Fish and Wildlife Service and agency cooperators continue to monitor the refuge tank. 11. Texas desert fish art – Harlan Bean* & Amanda Lord I have been studying Pecos Pupfish and am taking an art class this year. I am making an art project about Pecos Pupfish and their habitat. My art project is about Pecos Pupfish, and I am painting one in its habitat. I am using acrylics on a 12x16 inch canvas. I will be using my art to teach others at my middle school about Pecos Pupfish. 12. Digging in the dirt: Possible influence of soils & geology on the distribution of an endemic, desert-restricted salamander – Christopher Norment* & Eli Polzer A variety of evolutionary and ecological factors likely have affected the distribution of the Inyo Mountains salamander (IMS), Batrachoseps campi, a species of management concern endemic to the arid Inyo Mountains of eastern California. For example, isolation of the Inyo Mountains due to mountain-building episodes about 15.6 and 2.8 Ma (Lee et al., 2009, Tectonics 28: TC1001, doi:10.1029/2008TC002295) likely led to diversification of B. campi from ancestral Batrachoseps lineages approximately 2.5 Ma. IMS are documented from 24 localities; 22 (91.6 %) of these have permanent surface water. However, 20 (80 %) of the 25 sites in the Inyo Mountains where we and our colleagues have unsuccessfully searched for IMS appear to have permanent surface water and riparian vegetation that should support the species. Although imperfect detection may be an issue with amphibian surveys (Schmidt and Pellet, 2010, pp. 467-479 in C. K. Dodd, ed., Amphibian Ecology and Conservation), IMS may not occur at many of these sites. Several possible reasons for the species’ absence may include lack of colonization over evolutionary time, stochastic events such as severe flash floods, and an “extinction vortex” (Fagan and Holmes, 2006, Ecology Letters 9:51-60) caused by a combination of small population size, inbreeding depression, and habitat loss. Two additional factors that could affect distribution of the IMS include geology and soils. These could interact to affect availability of suitable below-ground refuges; soil moisture, which is critical for the IMS because it must breathe through moist skin; and the presence of sufficient organic material to support an adequate prey base. Anecdotally, we have observed that otherwise suitable sites with permanent surface water may lack IMS if they occur in soils with high clay content or that are formed from decomposing granite. In this very preliminary analysis, we used GIS to examine the distribution of IMS relative to soil and rock/deposit types in the Inyo Mountains. Sites supporting IMS appear to have soils with significantly lower clay content and bulk density than sites where IMS have not been found. Although Thomson et al. (2016, California Amphibian and Reptile Species of Special Concern, Univ. Calif. Press) state that the IMS is “largely restricted to patches of riparian habitat associated with perennial springs and limestone fissures,” it may occur in other rock/deposit types. Of the sites with IMS present, 71% of those were within areas of marine sedimentary and metasedimentary rocks, and 15% were within areas of granitic rocks. Conversely, only 32% of the sites where IMS have not been found were within areas of marine sedimentary and metasedimentary rocks, while 45% of the sites were within areas of granitic rocks. Although our conclusions are very tentative, they suggest that edaphic factors, and not just the presence of surface water and suitable vegetation, may be important in affecting the distribution of the IMS—and possibly other terrestrial species of management concern in Southwestern riparian ecosystems. 13. Vertical profiles of temperature & dissolved oxygen in Pahranagat Chub refuge – Montana Stevens Background. The Pahranagat Roundtail Chub Gila robusta jordani (PRTC) is a federally listed Cyprinid that historically occupied approximately 30 km of the now disjunct White River located in the Pahranagat valley of Lincoln County, NV. Due to primarily agricultural development the native range of the PRTC is now reduced to about 3.5 km of natural stream and 2.5 km of an earthen drain; all located on private lands in the valley. During irrigation season (March – October) water is diverted away from the 2.5 km section of drain that eventually dries over the season, eliminating almost half the available habitat. Along with reduced habitat, the PRTC is under immense pressure from seasonal water withdrawals, causing variation in habitat flow and temperature. The native range is also highly inundated with non-natives including the common carp, convict cichlids, common poeciliids, and crayfish. In response to the severely limited habitat range and quality, the United States Fish and Wildlife Service (USFWS) constructed a pond below Cottonwood Spring on the Pahranagat National Wildlife Refuge (PNWR) as a refugia for the PRTC. Multiple attempts to stock PRTC in the spring ended in mortality events that decimated the refuge population. USFWS suspects that variable geochemical and biological factors produced seasonally poor aquatic habitat for PRTC that could have contributed to the mortality events. Additionally, noted changes in winter water quality and clarity have coincided with fish mortality events. The previous attempts to stock PRTC into Cottonwood Spring that resulted in mortality occurred in 2011, 2016, & 2017. Following the final mortality event, the USFWS dedicated funding to a long term monitoring project of Cottonwood Spring. Primary Project Goals This project’s overall goals focus on monitoring, understanding, and reporting on how the biological and geochemical behavior of Cottonwood Spring change over time. This will be used to understand the seasonally influenced water quality changes that might be linked to PRTC mortality. All the data collected will be used in developing a report to help guide the restoration of the spring to be more suitable for PRTC survival. Presentation Focus The focus of this presentation will primarily be over temperature and dissolved oxygen vertical profiles taken at Cottonwood Spring as well as other biotic and abiotic factors affecting water quality at the spring. The poster will show data collected over the course of 2023 and how those parameters along with pond quality have changed over time. 14. Humpback Chub recruitment in light of changing environmental conditions – Pilar Rinker* & Randy Van Haverbeke The humpback chub, Gila cypha, population in Grand Canyon has been monitored using different protocols by several agencies beginning in the 1980s. In the early 2000s, the U.S. Fish and Wildlife Service (USFWS) began a monitoring project in the Grand Canyon that has evolved over time to monitor “aggregations” of humpback chub. An aggregation was defined as disjunct but reliably captured groups of humpback chub typically concentrated around springs and tributaries. Since 2010, USFWS monitoring methods have become relatively standardized and have tracked humpback chub abundances and relative abundances through time. Given recent environmental changes, humpback chub have expanded their range to include the entire western Grand Canyon and have been recorded among historic aggregation sites. In 2022, Lake Powell reached historic low elevations, warming the temperature of the river to its highest seen post-dam. This allowed the humpback chub to spawn and recruit in the mainstem at levels unseen since Glen Canyon Dam was built. This was evident as our 2022 data showed a sizeable cohort of age-0 chub and our 2023 data showed this cohort grew to the age-1 size class. The humpback chub population in Grand Canyon is as robust as it ever has been, but continually changing climate conditions may hinder their recovery as much as it has supported their expansion.