Demographic changes following mechanical removal of exotic brown trout in an Intermountain West (USA), high-elevation stream

Abstract -Exotic species present a great threat to native fish conservation; however, eradicating exotics is expensive and often impractical. Mechanical removal can be ineffective for eradication, but nonetheless may increase management effectiveness by identifying portions of a watershed that are strong sources of exotics. We used mechanical removal to understand processes driving exotic brown trout (Salmo trutta) populations in the Logan River, Utah. Our goals were to: (i) evaluate the demographic response of brown trout to mechanical removal, (ii) identify sources of brown trout recruitment at a watershed scale and (iii) evaluate whether mechanical removal can reduce brown trout densities. We removed brown trout from 2 km of the Logan River (4174 fish), and 5.6 km of Right Hand Fork (RHF, 15,245 fish), a low-elevation tributary, using single-pass electrofishing. We compared fish abundance and size distributions prior to, and after 2 years of mechanical removal. In the Logan River, immigration to the removal reach and high natural variability in fish abundances limited the response to mechanical removal. In contrast, mechanical removal in RHF resulted in a strong recruitment pulse, shifting the size distribution towards smaller fish. These results suggest that, before removal, density-dependent mortality or emigration of juvenile fish stabilised adult populations and may have provided a source of juveniles to the main stem. Overall, in sites demonstrating strong density-dependent population regulation, or near sources of exotics, short-term mechanical removal has limited effects on brown trout populations but may help identify factors governing populations and inform large-scale management of exotic species

Exploring Metapopulation-Scale Suppression Alternatives for a Global Invader in a River Network Experiencing Climate Change

Invasive species can dramatically alter ecosystems, but eradication is difficult, and suppression is expensive once they are established. Uncertainties in the potential for expansion and impacts by an invader can lead to delayed and inadequate suppression, allowing for establishment. Metapopulation viability models can aid in planning strategies to improve responses to invaders and lessen invasive species’ impacts, which may be particularly important under climate change. We used a spatially-explicit metapopulation viability model to explore suppression strategies for ecologically-damaging invasive brown trout (Salmo trutta), established in the Colorado River and a tributary within Grand Canyon National Park. Our goals were to: 1) estimate the effectiveness of strategies targeting different life stages and subpopulations within a metapopulation, 2) quantify the effectiveness of a rapid response to a new invasion relative to delaying action until establishment; and 3) estimate whether future hydrology and temperature regimes related to climate change and reservoir management affect metapopulation viability and alter the optimal management response. We included scenarios targeting different life-stages with spatially-varying intensities of electrofishing, redd destruction, incentivized angler harvest, piscicides, and a weir. Quasi-extinction (QE) was obtainable only with metapopulation-wide suppression targeting multiple life-stages; subpopulations were most sensitive to age-0 and large adult mortality. The duration of suppression needed to reach QE for a large established subpopulation was triple compared to a rapid response to a new invasion. Isolated subpopulations were vulnerable to suppression; however, connected tributary subpopulations enhanced metapopulation persistence by serving as climate refuges. Water shortages driving changes in reservoir storage and subsequent warming would cause brown trout declines, but metapopulation QE was only achieved by re-focusing and increasing suppression. Our modeling approach improved our understanding of invasive brown trout metapopulation dynamics, which could lead to more focused and effective invasive species suppression strategies, and ultimately, maintenance of populations of endemic fishes

Resilient and Rapid Recovery of Native Trout After Removal of a Non-Native Trout

While the importance of reducing impacts of non-native species is increasingly recognized in conservation, the feasibility of such actions is highly dependent upon several key uncertainties including stage of invasion, size of the ecosystem being restored, and magnitude of the restoration activity. Here, we present results of a multi-year, non-native brown trout (Salmo trutta) removal and native Bonneville cutthroat trout (Oncorhynchus clarkii utah) response to this removal in a small tributary in the Intermountain West, United States. We monitored trout for 10 years prior to the onset of eradication efforts, which included 2 years of mechanical removal followed by 2 years of chemical treatment. Cutthroat trout were then seeded with low numbers of both eggs and juvenile trout. We monitored demographics and estimated population growth rates and carrying capacities for cutthroat trout from long-term depletion estimate data, assuming logistic population growth. Following brown trout eradication and initial seeding efforts, cutthroat trout in this tributary have responded rapidly and have approached their estimated carrying capacity within 6 years. Population projections suggest a 95% probability that cutthroat trout will be at or above 90% of their carrying capacity within 10 years of the eradication of brown trout. Additionally, at least four age-classes are present including adults large enough to satisfy angling demand. These results demonstrate native trout species have substantial capacity to rapidly recover following removal of invasive species in otherwise minimally altered habitats. While tributaries such as like this study location are likely limited in extent individually, collectively they may serve such as source populations for larger connected systems. In such cases, these source populations may provide additional conservation potential through biotic resistance

Assessment of Potential Augmentation and Management Strategies for Razorback Sucker \u3cem\u3eXyrauchen texanus\u3c/em\u3e in Lake Mead and Grand Canyon: A 2021 Science Panel Summary

Razorback Sucker Xyrauchen texanus is a large-bodied, long-lived species endemic to the Colorado River Basin. This species historically ranged throughout the basin from the Colorado River delta in Mexico to Wyoming and Colorado. Currently, the species persists ,in a small portion of its historical range with the help of intensive management efforts including augmentation. Recruitment to adult life stages is extremely limited in the wild, but is documented consistently in Lake Mead. Research and monitoring efforts in Lake Mead are ongoing since 1996 and have recently expanded to include the Colorado River inflow area and portions of lower Grand Canyon. Despite evidence of recruitment, the current population size in Lake Mead and Grand Canyon is believed to be small (data) and susceptible to stochastic effects. This raised interest in the potential to augment the population to prevent loss of genetic diversity and increase abundance and distribution in general, as well as explore recruitment bottlenecks. To address critical uncertainties surrounding this management option and to brainstorm other potential options, a Planning Committee and Steering Committee made up of representatives of state (Arizona, Nevada), tribal (Hualapai Tribe, Navajo Nation), and federal (Bureau of Reclamation, National Park Service, and U.S. Fish and Wildlife Service) management agencies convened an Expert Science Panel (ESP; 2021), to consider augmentation and management strategies for Razorback Sucker in Lake Mead and Grand Canyon. The purpose of this report is to summarize those findings

BioTIME: A database of biodiversity time series for the Anthropocene.

MotivationThe BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.Main types of variables includedThe database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grainBioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).Time period and grainBioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.Major taxa and level of measurementBioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.Software format.csv and .SQL

Weber River Metapopulation and Source-Sink Dynamics of Native Trout and Nongame Fishes

Bonneville cutthroat trout (Oncorhynchus clarkii utah) presently occupy a variety of habitats from small streams to larger rivers and lakes that drain into the Bonneville Basin. As a result of continued threats to the subspecies and its habitat, the Bonneville cutthroat trout is designated by the State of Utah as a “conservation species” managed under a formal conservation agreement intended to preclude the need for listing under the federal Endangered Species Act. The Weber River in northern Utah is somewhat unusual for the intermountain west in that it is still home to native and endemic Bonneville cutthroat trout and bluehead sucker (Catostomus discobolus), yet is highly regulated and connectivity has been significantly reduced due to barriers to movement and migration. Despite the prevalence of these factors in the Weber River, both resident and fluvial Bonneville cutthroat trout as well as large, mature bluehead sucker were thought to be relatively common, highlighting the potential of this watershed for native fish conservation and restoration. The overall goal of this study was to identify the historical and contemporary importance of mainstem connectivity and tributaries to maintaining the population viability and persistence of these two species. To meet that goal, we used a multifaceted approach to describe the metapopulation structure and the importance of the tributaries in providing connectivity among subpopulations, at the watershed scale. This project was initiated in 2011 and the field work was completed in 2013