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Similar to many freshwater ecosystems, the Laurentian Great Lakes of North America have undergone numerous anthropogenic stressors resulting in considerable loss of biodiversity and habitat. Among Great Lakes fishes, the coregonine sub-family has endured the most extensive declines, including extinction of several species (Coregonus johannae, C. alpenae, and C. kiyi orientalis) and at least 10 instances of local extirpations of other species (C. nigripinnis, C. reighardi, C. zenithicus, C. hoyi, and C. artedi) across all 5 lakes, much of which occurred prior to the 1960s owing to overfishing, interactions with non-indigenous species, and habitat loss. Despite these declines, no federal-, provincial-, or state-mandated actions were ever implemented to conserve coregonine diversity, potentially because so much of the coregonine declines occurred prior to the enactment of federal conservation legislation. Possible explanations for inaction since enactment of that legislation include insufficient data on biological vulnerability or threats, unresolved taxonomy, and limited support from the fishery management agencies and their stakeholders prior to the 2000s. In recent decades, however, several fishery management agencies have undertaken efforts to re-introduce coregonine diversity. These efforts helped lead to development of a science-based framework to restore coregonines that was universally endorsed by fishery managers representing eight U.S. states, four U.S. tribal organizations, and the province of ON, Canada, in May 2018. The basin-wide framework is based on principles of conservation biology and adaptive management. We describe details of its key steps, including planning, restoring, and evaluating, while also describing recent implementation efforts to develop methods, improve available resources, and enhance coordination across the basin. Although our paper describes a regional effort to restore native coregonines, our adaptive-management approach could be used by other multi-agency stakeholders seeking to conserve or restore native fishes. [ABSTRACT FROM AUTHOR]

Abstract We examined why the lower Little Colorado River (LCR), Arizona continues to be dominated by four native fish species despite decades of encroachment by nine nonnative species. Most perennial flow begins at Blue Spring, located at river kilometer (RKM) 20.74 above the LCR's mouth, which is supplemented downriver by other springs. Blue Spring's water is extremely supersaturated with dissolved CO2 (658 mg/L), and at baseflow the CO2 concentrations apparently functioned as a fish-barrier for about 1 km further downriver until it outgassed to 288 mg/L. Thereafter, CO2 outgassed to 202 mg/L by the top of Chute Falls (RKM 14.20) and 76 mg/L near the river's mouth. Chute Falls, and high CO2 levels above it, obstruct upriver, but not downriver, fish movements; however, we still captured fishes from eight nonnative species above this falls. Our findings indicate most warmwater nonnative fishes in the LCR were immigrants from upriver sources within and bordering the intermittent corridor that invaded the system during floods, while most coldwater trout invaded from the Colorado River. Most nonnative species failed or were severely limited at reproducing progeny in the LCR, except occasionally by channel catfish Ictalurus punctatus and fathead minnow Pimephales promelas in the lower 13.57 km corridor, which was likely related to CO2. Correlation tests suggested severe flood and/or suspended sediment regimes reduced populations of fathead minnows, red shiners Cyprinella lutrensis, and plains killifish Fundulus zebrinus in the LCR. Conversely, severe suspended sediment regimes (especially ≥60,000 mg/L) increased channel catfish, black bullhead Ameiurus melas, and common carp Cyprinus carpio, hypothetically by paralyzing these fishes upriver, whereby many drifted downstream and recovered in the lower LCR; however, their abundances decreased after prolonged periods of high CO2. Nonnative fishes are controlled in the LCR by the system's endemic abiotic conditions. [ABSTRACT FROM AUTHOR]