Recovery of freshwater invertebrates in alpine lakes and streams following eradication of nonnative trout with rotenone

Nonnative fish eradication via the piscicide rotenone is an effective tool for fisheries management and conservation of native species. However, the long-term effects on non-target organisms, including benthic invertebrates and zooplankton in alpine lakes, are under-studied and are poorly understood. As part of a landscape-scale native fish conservation project, we assessed the effects of 50 ppb rotenone on the aquatic invertebrate community by comparing pre- and post-rotenone treatment density and diversity metrics of benthic invertebrates and zooplankton in 13 alpine lakes and their outlets in Montana, USA. Across study sites, decreases in density and diversity of some invertebrates, including Ephemeroptera, Plecoptera, and Trichoptera taxa, were observed the year following rotenone treatment, and within three years, densities and diversities were similar to and sometimes higher than pre-treatment values. These results demonstrate resilience of aquatic invertebrate communities following rotenone exposure in alpine lakes and streams and informs fisheries managers for planning rotenone projects and monitoring recovery of non-target organisms. Further studies will be useful to evaluate the mechanisms driving invertebrate recovery rates, including downstream drift from nontreated areas and terrestrial adult dispersal.

Two Ocean Pass: An Alternative Hypothesis for the Invasion of Yellowstone Lake by Lake Trout, and Implications for Future Invasions

Preventing the interbasin transfer of aquatic invasive species is a high priority for natural resource managers. Such transfers can be made by humans or can occur by dispersal through connected waterways. A natural surface water connection between the Atlantic and Pacific drainages in North America exists at Two Ocean Pass south of Yellowstone National Park. Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri used this route to cross the Continental Divide and colonize the Yellowstone River from ancestral sources in the Snake River following glacial recession 14,000 bp. Nonnative lake trout Salvelinus namaycush were stocked into lakes in the Snake River headwaters in 1890 and quickly dispersed downstream. Lake trout were discovered in Yellowstone Lake in 1994 and were assumed to have been illegally introduced. Recently, lake trout have demonstrated their ability to move widely through river systems and invade headwater lakes in Glacier National Park. Our objective was to determine if lake trout and other nonnative fish were present in the connected waters near Two Ocean Pass and could thereby colonize the Yellowstone River basin in the past or future. We used environmental DNA (eDNA), electrofishing, and angling to survey for lake trout and other fishes. Yellowstone cutthroat trout were detected at nearly all sites on both sides of the Continental Divide. Lake trout and invasive brook trout S. fontinalis were detected in Pacific Creek near its confluence with the Snake River. We conclude that invasive movements by lake trout from the Snake River over Two Ocean Pass may have resulted in their colonization of Yellowstone Lake. Moreover, Yellowstone Lake may be vulnerable to additional invasions because several other nonnative fish inhabit the upper Snake River. In the future, eDNA collected across smaller spatial intervals in Pacific Creek during flow conditions more conducive to lake trout movement may provide further insight into the extent of non-native fish invasions in this stream.

From Catastrophe to Recovery: Stories of Fishery Management Success

<i>Abstract.</i>—Fish assemblages in the Willamette River basin (Oregon) were once substantially degraded by water pollution, channelization, dams, nonnative fish, and conversion of natural forest and savanna to agriculture and urbanization. Restoration actions have included basinwide waste treatment, physical habitat rehabilitation, recovery of the Oregon Chub <i>Oregonichthys crameri</i> to stable status, and stocking reductions of nonnative fish to protect native fish. State and federal sewage treatment regulations and funding, federal endangered species regulations and funding, and reduced funding and support for stocking nonnative trout led to those rehabilitated fish assemblages. Periodic fish and habitat monitoring has documented the following improvements in fish assemblages: (1) decreased occurrences of pollution-tolerant species and increased occurrences of pollution-sensitive species and native main-stem species, (2) increased number of abundant Oregon Chub populations, and (3) persistence of resident native Rainbow Trout <i>Oncorhynchus mykiss</i>. Notably, no known extinctions of native fish species have occurred in the Willamette River, water quality index scores in the lower river have improved from poor to fair, and water quality in the upper river remains good to excellent. In conclusion, enactment of laws and regulations for environmental protection and the collective actions of state and federal agencies, tribes, municipal governments, universities, land trusts and conservation groups, watershed councils, and private landowners have led to a substantially rehabilitated river. However, population and economic growth, climate change, nonnative fish, winter steelhead (anadromous Rainbow Trout) and spring Chinook Salmon <i>O. tshawytscha</i> listings, a superfund site, channel alterations, toxic substances, poor fish passage at dams, and altered flow regimes remain challenges. Four lessons learned are that (1) pollution control and improved water quality and flows are essential to the recovery and persistence of native fish populations, (2) recovery of endangered species is achievable but requires knowledge of their life history needs, (3) the greater ecological fitness of native stocks facilitates their persistence, and (4) research and monitoring, combined with public communication and collaboration, are essential for habitat and native fish assemblage rehabilitation.

Factors associated with the success of native and nonnative species in an unfragmented arid-land riverscape

Native fish persistence is threatened by the establishment and spread of nonnatives. Identifying environmental and biotic factors associated with the success of co-occurring native fishes and nonnative taxa is central to identifying mechanisms responsible for native declines and nonnative expansion. We related physicochemical variables, food resources, and community composition to the success (secondary production) of native and nonnative fishes, tadpoles, and crayfish across six sites in three reaches (tributary, canyon, and valley) during 2008–2011 in the Gila River, New Mexico. Native fish success was greater than nonnative success across a range of physicochemical conditions, basal resource supply rates, and nonnative communities, although nonnative fish, tadpole, and crayfish success could approach or exceed that of native fishes in canyon habitats, a warm-water tributary, or in downstream valley sites, respectively. Native fish success was lowest in canyon reaches, when flathead catfish (Pylodictis olivaris) and common carp (Cyprinus carpio) were highly productive. These results demonstrate the potential for native fish persistence in the presence of nonnatives in physically unmodified streams, highlighting the importance of habitat preservation for native conservation.