Clark Hubbs

Objective In many Great Plains rivers, functional turnover—the change in proportional dominance of members in biological communities that fill certain ecological roles—has occurred due to impoundment and habitat alteration. The Powder River of Montana and Wyoming remains one of the few unregulated prairie rivers, but long‐term monitoring is limited, so we analyzed changes over time at the functional, assemblage, and species levels.MethodsWe used fish sampling data from 43 different sources collected from 1893 to 2022 to analyze trends in fish communities.ResultAcross the main‐stem Powder River, Sand Shiner Miniellus stramineus and Channel Catfish Ictalurus punctatus substantially increased in abundance, whereas Sturgeon Chub Macrhybopsis gelida decreased. While most other species did not show significant changes in relative abundance (although the always rare Lake Chub Couesius plumbeus may have been extirpated), significant functional turnover occurred in the upper river due to increases in generalist feeders, predators, omnivores, and cavity‐guarding species, with declines in benthic feeders, invertivores, and pelagic broadcast spawners, among others. Community and functional changes were more substantial in the upper river than in the lower river, possibly due to augmented streamflow from a major tributary.ConclusionFunctional turnover within the upper river was substantial despite the relative stability of most individual species, even when the Sand Shiner—the most significantly increasing species—was excluded from analysis. This suggests small but consistent increases and decreases within functional groups, which cumulatively are likely impacting the ecosystem. We hypothesize a complex set of mechanisms causing these changes that offer avenues for future work. The collation of data from disparate studies and the resampling of even a limited number of historical fish collection locations can greatly aid in identifying potential fish community changes in systems where monitoring is limited.

Updated records related to coexisting species, the presence of invasive species, and the presence or absence of Threatened, Endangered, or Species of Greatest Conservation Need are a necessary component of wildlife conservation. Here, we compile a list of historically documented fish species found in San Felipe Creek and report updated occurrence from recent sampling events. Of the anticipated 49 species within San Felipe Creek, we documented 16 between 2019 and 2022. We observed Devils River minnow (Dionda diaboli), a federally Threatened species, during all sampling events. Additionally, we confirmed the presence of three state Threatened species and one Species of Greatest Conservation Need. We also document continued presence of the invasive suckermouth catfish (Hypostomus plecostomus) and blue tilapia (Oreochromis aureus). Researchers may use species occurrence data provided by these efforts to assess future assemblage changes within the San Felipe Creek system.

Desert spring systems of the American southwest hold high local fish endemism and are ranked among the most threatened ecosystems in the world. The prioritization of conservation resources to protect species living within these arid landscapes requires knowledge of species abundance and distribution. The plight of Conchos pupfish (Cyprinodon eximius) is representative of freshwater fishes the world over, including population extirpations caused by human poisoning of streams and reservoir construction, to the extent that the species was once considered extinct in the USA. We developed a distance‐sampling framework to monitor Conchos pupfish abundance and coupled this approach with species distribution modeling to guide conservation actions. Our multiscale approach included surveying abundances within 5‐m transects at three reaches of the Devils River, where the last known USA populations persist. We combined this fine‐scale analysis with species distribution modeling for stream segments across the range of the species in Mexico and USA. Modeling revealed Conchos pupfish abundance among transects was negatively correlated with current velocity and detection was negatively correlated with water depth. Estimated abundance at a reach where the species was previously reintroduced was greater than other reaches combined in November 2019, lowest in March 2021 when reach water levels were very low, then equivalent with other reaches by October 2021 after water returned to the reach. Modeled Conchos pupfish distribution illustrated a high probability of occurrence on the periphery of the species' overall range within Texas, USA and broadly across Chihuahua, Mexico, where proposed protected areas might benefit the species. Our study provides conservation guidance by establishing (1) baseline and trajectory values for abundance, (2) transect locations where abundances might be managed within existing protected areas, (3) reaches where high abundances could be used for future repatriation, and (4) stream segments where future surveys might be conducted to assess conservation opportunities.

The decreasing freshwater biodiversity trend can be attributed to anthropogenic impacts in terms of climate and land cover change. For targeted conservation efforts, mapping and understanding the distribution of freshwater organisms consists of an important knowledge gap. Spatial modelling approaches offer valuable insights into present-day biodiversity patterns and potential future trajectories, however methodological constraints still hamper the applicability of addressing future climate and land cover change concurrently in one modelling workflow. Compared to climate-only projections, spatially explicit and high-resolution land cover projections have seen less attention, and the lack of such data challenges modelling efforts to predict the possible future effects of land cover change especially on freshwater organisms. Here we demonstrate a workflow where we downscale future land cover projection data from the Shared Socioeconomic Pathway (SSP) scenarios for South America at 1 km2 spatial resolution, to then predict the future habitat suitability patterns of the Colombian fish fauna. Specifically, we show how the land cover data can be converted from plain numbers into a spatially explicit representation for multiple SSP scenarios and at high spatial resolution, employing freshwater-specific downscaling aspects when spatially allocating the land cover category grid cells, and how it can be fitted into an ensemble species distribution modelling approach of 1209 fish species. Our toolbox consists of a suite of open-source tools, including Dinamica EGO, R, GRASS GIS and GDAL, and we provide the code and necessary steps to reproduce the workflow for other study areas. We highlight the feasibility of the downscaling, but also underline the potential challenges regarding the spatial scale and the size of the spatial units of analysis.

The Tres Marías archipelago in the central Mexican Pacific is a protected area that has a complex geological history due to its tectonic setting. This study describes an integrative analysis of the biogeographical affinities of the biota inhabiting the islands. A biotic component analysis showed a close relationship between the islands and the Pacific Lowlands and Veracruzan biogeographical provinces, whereas a cladistic biogeographical analysis additionally showed a Nearctic affinity with the Sonoran biogeographical province. The biogeographical affinity patterns, based on the distribution of the sister group of each endemic species, revealed three distinct patterns: Neotropical, Sonoran-Neotropical and Nearctic-Neotropical. The study recognized that the Tres Marías Islands are a region of great biological complexity where the biota of the Pacific Lowlands and the Veracruzan provinces intersect, with a predominantly Neotropical affinity. In this biogeographical analysis, information on the biotic assemblage and the geological history of the Tres Marías Islands are integrated and discussed. The biotic assembly of the islands must have occurred via both vicariance and dispersal at different geological times, related to opening of the Gulf of California (Miocene–Pleistocene) as well as to periods of glaciation (Pleistocene).

Blue sucker (Cycleptus elongatus) populations occur in the Mississippi River and Gulf of Mexico drainages of North America and are negatively affected by habitat fragmentation and flow regime alteration caused by dams. During fish assemblage surveys in August of 2022, we collected five juvenile blue suckers (312–428 mm total length) in the Angelina River upstream of Sam Rayburn Reservoir in East Texas (46,335 ha surface area) where the occurrence of the species was previously unconfirmed. Given this unexpected finding, we (1) analyzed mesohabitat associations to compare habitats we sampled with reports in the literature and (2) reviewed blue sucker occurrences in state, national, and global databases across historical (1950–1980) and contemporary (1981–2022) time periods to assess occurrence across gradients of habitat fragmentation and streamflow regulation. The blue sucker population in the Angelina River upstream of Sam Rayburn Reservoir was previously unconfirmed but is within the native range. Mesohabitats occupied by blue suckers were consistent with literature reports, including fast velocity, shallow depth, and coarse substrates. The low degree of regulation (19% of natural runoff stored by upstream reservoirs) and a high degree of habitat connectivity (287 rkm of unfragmented mainstem habitat) for the Angelina River upstream of Sam Rayburn Reservoir matched range‐wide patterns of persistence within relatively intact (unfragmented and unregulated) or remnant (fragmented but unregulated) riverscapes. Our review reveals that blue sucker populations might persist (1) in remnant river fragments where local habitat conditions are appropriate and (2) where effects of habitat fragmentation and flow regulation are not coupled.

Largemouth Bass (Micropterus salmoides, LMB) and Smallmouth Bass (Micropterus dolomieu, SMB) are among the most highly invasive species across the globe, but are simultaneously among the most highly sought-after game fish. To explain these disparate views, data on invasive status and angling participation of these two species were compiled at the country level. Largemouth Bass were found established in 62 countries on five continents, whereas SMB were found established in only nine countries on the same five continents. Invasive risk assessments were disparate between the species, with more for SMB (N = 29) than LMB (N = 27). In every instance save one (Finland), SMB were considered “invasive” compared to LMB, which were “invasive” in only 74% of assessments. Twenty-eight countries with non-native black bass have groups that participate in high-profile fishing tournament such the Black Bass World Championship, BASS (Bass Anglers Sportsmans Society) Nation, and Major League Fishing. Most countries with fishing tournaments occur in countries with established LMB populations than in countries with established SMB populations, suggesting a greater economic importance on LMB fishing. The struggle between conserving biodiversity and relying upon economic benefits from fishing for introduced species is a wicked problem likely to continue into the future.

The biotic assembly of the Revillagigedo Archipelago, Mexico, was analysed under an evolutionary biogeographic framework. We undertook a parsimony analysis of endemicity with progressive character elimination of 194 plant and animal species, which allowed us to identify the archipelago as a complex area or node where Nearctic and Neotropical biotic components overlap. We undertook a cladistic biogeographic analysis using the phylogenetic information of 42 taxon-area cladograms, from which one general-area cladogram was obtained: (Revillagigedo, (Sonoran, (Baja California, (Veracruzan, Pacific Lowlands)))). These results suggest that the Revillagigedo Archipelago may be classified as a province, although we prefer to keep it as a district of the Pacific Lowlands province. We identified two cenocrons (temporally integrated set of taxa) that can be dated to the Pliocene–Pleistocene: one Nearctic that dispersed from the Baja California Peninsula, and another Neotropical where the species dispersed from the Pacific coast to the islands. The geological information and the general-area cladograms allowed us to propose a geobiotic scenario for the archipelago where the islands are probably the result of volcanism associated with the oceanic Mathematician Ridge, and the arrival of the cenocrons to the archipelago may have occurred during the Pliocene–Pleistocene, after the islands were available for colonisation.

Freshwater biodiversity is declining faster than terrestrial and marine biodiversity. The protection and restoration of aquatic habitats are based, in part, on stemming this decline. We conducted a spatial conservation assessment of native fishes in the Lahontan and central Nevada basins using core-area zonation. The complementarity-based assessment yielded a landscape value (rank) of all subwatersheds (12-digit hydrologic unit code; ~12,000 ha) whereby high-ranking subwatersheds, as a set, maximized the representation of all native species, subspecies, and the within-species ecological diversity of salmonids, while accounting for aquatic connectivity and risk of aquatic habitat degradation. The high-ranking subwatersheds encapsulated small patches of habitat inhabited by endemic desert fishes, as in the Ash Meadows National Wildlife Refuge. They also highlighted clusters of high-value subwatersheds, such as in the Truckee River watershed that has extant populations of, and historical habitat for, Lahontan cutthroat trout in its headwaters, with species such as the mountain whitefish with migratory life histories, and endemic cui-ui, Chasmistes cujus, at Pyramid Lake—a terminal lake. Both the Truckee River headwaters and Pyramid Lake have been recipients of ongoing native fish conservation efforts. The landscape rankings will be used by the Desert Fish Habitat Partnership to inform regional conservation investments, and the rankings are available for broader use by resource agencies working on native fish conservation at landscape scales.

Freshwater ecosystems are highly vulnerable to the detrimental impacts of both biological invasions and climate change. Piscivorous alien fishes drive populations of small-bodied native fishes to extinction and warming is already driving extreme temperature events in lakes and rivers globally. Here, we use Ecological Niche Modelling (ENM) to predict how climate change will alter the geographical space of six alien fishes and five native fish genera (which include multiple endemic species) in Turkey, a hotspot of freshwater fish diversity. The models predicted that the geographical space of the alien fishes already present in Turkey would generally increase (including pikeperch Sander lucioperca and perch Perca fluviatilis ), but with the most substantial increases in largemouth bass Micropterus salmoides , a species not yet present in Turkey but that is invasive in countries nearby and is highly popular for sport angling. For the native fish genera, general predictions were for reduced geographical space, especially in the south and east of the country, suggesting the endemic species will become increasingly imperilled in future. Their populations will also be at increasing risk of deleterious impacts from the alien piscivores, as the predictions were also for increasing overlaps in the geographical space of both the alien fishes and native fish genera. These predictions suggest that the conservation of these endemic species need to consider measures on preventing both the introduction of alien species (e.g. largemouth bass) and the further dispersal of extant alien species (e.g. pikeperch), as well as habitat interventions that will limit the effects of climate change on their populations. These results also indicate that the combination of climate change and alien invasions could have substantial impacts on—and similar—hotspots of freshwater diversity.