Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem.

Diet plasticity is a common behavior exhibited by piscivores to sustain predator biomass when preferred prey biomass is reduced. Invasive piscivore diet plasticity could complicate suppression success; thus, understanding invasive predator consumption is insightful to meeting conservation targets. Here, we determine if diet plasticity exists in an invasive apex piscivore and whether plasticity could influence native species recovery benchmarks and invasive species suppression goals. We compared diet and stable isotope signatures of invasive lake trout and native Yellowstone cutthroat trout (cutthroat trout) from Yellowstone Lake, Wyoming, U.S.A. as a function of no, low-, moderate-, and high-lake trout density states. Lake trout exhibited plasticity in relation to their density; consumption of cutthroat trout decreased 5-fold (diet proportion from 0.89 to 0.18) from low- to high-density state. During the high-density state, lake trout switched to amphipods, which were also consumed by cutthroat trout, resulting in high diet overlap (Schoener’s index value, D = 0.68) between the species. As suppression reduced lake trout densities (moderate-density state), more cutthroat trout were consumed (proportion of cutthroat trout = 0.42), and diet overlap was released between the species (D = 0.30). A shift in lake trout δ13C signatures from the high- to the moderate-density state also corroborated increased consumption of cutthroat trout and lake trout diet plasticity. Observed declines in lake trout are not commensurate with expected cutthroat trout recovery due to lake trout diet plasticity. The abundance of the native species in need of conservation may take longer to recover due to the diet plasticity of the invasive species. The changes observed in diet, diet overlap, and isotopes associated with predator suppression provides more insight into conservation and suppression dynamics than using predator and prey biomass alone. By understanding these dynamics, we can better prepare conservation programs for potential feedbacks caused by invasive species suppression.

Multiyear drought is projected to increase in frequency and duration in arid and semiarid regions across the world, threatening native species and ecosystem function. The effects of multiyear drought are often exacerbated by human water use for consumption, energy production, and agriculture, which, in lentic ecosystems, manifest in reduced lake elevation and altered habitat for aquatic species. Here, we demonstrate that decreasing lake levels, associated with drought and water management, reduce the availability of littoral cobble habitat to fishes by creating an elevation‐explicit littoral habitat map. We combined long‐term fish catch data and a lake elevation time series with our elevation‐explicit littoral habitat map to test whether fish species population demographics are related to drought‐driven changes in littoral habitat. We surveyed the littoral zone of Bear Lake, Utah and Idaho, U.S.A., from full pool to a depth of >12 m, totalling 94.86 km2 surveyed. As lake elevation decreased >6 m from full pool to the lowest historical elevation, the area of littoral cobble decreased by >97%. Bear Lake sculpin (Cottus extensus, Cottidae), a cold‐water fish species which relies on cobble for reproduction, catch per unit effort decreased by >75% with littoral cobble, and year class strength declined by as much as 86%, but varied across age. We predicted the response of age‐0 to age‐4 sculpin under high and low cobble availability. Our simulations predict a 60%–85% decline in juvenile sculpin CPUE (age‐2 and younger) when cobble availability decreases from the 95th to 5th percentile. Our study provided a unique opportunity to identify quantitative linkages between climate‐driven littoral habitat loss and an ecologically important profundal fish species, expanding our understanding of potential future pathways through which climate change may affect lentic ecosystems and fishes.

Despite unprecedented scientific productivity, Earth is undergoing a sixth mass extinction. The disconnect between scientific output and species conservation may be related to scientists studying the wrong species. Given fishes have a high extinction rate, we assessed the paradox between scientific productivity and science needed for conservation by comparing scientific output created for critically endangered fishes and game fishes. We searched 197,866 articles (1964–2018) in 112 journals for articles on 460 critically endangered fishes, 297 game fishes, and 35 fishes classified as critically endangered and game fish—our analysis included freshwater and marine species. Only 3% of the articles in the final database were on critically endangered fishes; 82% of critically endangered fishes had zero articles. The difference between the number of articles on game fishes and critically endangered fishes increased temporally with more articles on game fishes during the extinction crisis. Countries with 10 or more critically endangered fishes averaged only 17 articles from 1964 to 2018. Countries with the most critically endangered fishes are most in need of science. More scientific knowledge is needed on critically endangered fishes to meet the challenges of conserving fishes during the sixth mass extinction.

Microplastics have been documented in aquatic and terrestrial ecosystems throughout the world. However, few studies have investigated microplastics in freshwater fish diets. In this study, water samples and three trophic levels of a freshwater food web were investigated for microplastic presence: amphipods (Gammarus lacustris), Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), and lake trout (Salvelinus namaycush). Microplastics and other anthropogenic materials were documented in water samples, amphipods, and fish, then confirmed using FTIR (Fourier-transform infrared) and Raman spectroscopy. Our findings confirmed the presence of microplastics and other anthropogenic materials in three trophic levels of a freshwater food web in a high-elevation lake in a national park, which corroborates recent studies implicating the global distribution of microplastics. This study further illustrates the need for global action regarding the appropriate manufacturing, use, and disposal of plastics to minimize the effects of plastics on the environment.

No abstract

Invasive species require management to mitigate their harmful effects on native biodiversity and ecosystemprocesses. However, such management can also have negative, unintended consequences on non-target taxa,ecosystem processes, and food web dynamics. In Yellowstone Lake, invasive lake trout (Salvelinus namaycush)have caused a decline in the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population. Tosuppress the invader, lake trout carcasses are deposited on the species’ spawning sites, causing embryo mortalityby reducing dissolved oxygen as they decay. The non-target effects of carcass deposition are unknown, but benthicinvertebrates may be sensitive to reductions in dissolved oxygen. Benthic invertebrate taxa have varying hypoxiatolerances; caddisflies of the family Limnephilidae are hypoxia sensitive whereas the amphipods Gammarus lacustrisand Hyalella azteca are hypoxia tolerant. Both taxa are widespread and abundant in Yellowstone Lake andcomprise a large proportion of fish diets, and changes in their abundances could therefore alter food web dynamics.We conducted an in situ experiment to determine if carcass deposition causes mortality in these two benthic invertebratetaxa. The probability of mortality for caddisflies was 3.15 times higher in carcass treatments compared tocontrols, while amphipod mortality did not change in response to carcass treatment. Amphipods, which contributemost significantly to fish diets, are unlikely to be reduced in response to carcass deposition, which is confined to asmall fraction of the lake where lake trout spawn, limiting the possibility for lake-wide effects. We conclude thatcarcass deposition is unlikely to alter the availability of invertebrates as a food source for fish in Yellowstone Lake.

Excessive fishing pressure can induce population declines or complete collapse of fisheries. Unless commercial and recreational fisheries for K‐selected fishes, or those with slow growth and late maturation, are carefully managed, declines in abundance or fishery collapse is probable. Paddlefish Polyodon spathula,are a K‐selected species that experienced historical declines in abundance as a result of habitat degradation and overfishing. Mark‐recapture studies are well‐suited for long‐lived fishes by providing information on population density and vital rates. For sustainable commercial or recreational fisheries targeting species such as the paddlefish, managers require accurate estimates of population vital rates including survival, abundance, and exploitation. We used a Montana Fish, Wildlife & Parks (MFWP) mark‐recapture dataset and modified Jolly‐Seber (POPAN) models to estimate survival, recapture, probability of entry, and abundance of 8,518 tagged paddlefish over a 25‐year period. With many supporting estimates including stable survival (0.92 for females, mean of 0.82 for males), low exploitation rates (means of 2.6% for females and 2.9% for males), and stable abundance estimates (25‐year mean of 12,309 individuals for both sexes), the Fort Peck paddlefish population appears to be stable and well‐managed over the past 25 years. Presently, this is the only study focused on paddlefish in North America that has estimated survival and abundance for both male and female paddlefish using contemporary analyses. This research provided a unique opportunity to highlight that the effort exerted by management agencies to collect long‐term field data is extremely useful to our understanding of fish populations and management.