Invasive species can produce complex and unpredictable effects across multiple trophic levels through a combination of direct and indirect pathways. Invasive silver carp (Hypophthalmichthys molitrix) exert substantial pressure on the link between primary production and intermediate trophic levels in large rivers of the Midwestern USA. The goal of our manuscript was to describe the silver carp population invasion in the Illinois River (Illinois, USA) and explore the potential effects of silver carp on the native biota. We obtained 22 years of data from three long‐term monitoring programmes for phytoplankton, zooplankton, and age‐0 and adult native fishes. To determine when silver carp started affecting native biota, we used nonlinear regression to estimate the change point in silver carp biomass. We then used piecewise linear regression to separately model the response of phytoplankton and age‐0 and adult native fishes, using the model‐estimated change point in silver carp biomass. We tested for differences in taxon‐specific zooplankton density and biomass between pre‐ and post‐establishment periods using generalised linear models. To explore associations between native biota, silver carp and other potential drivers, we used single‐factor linear‐regression models in an information theoretic‐based approach. Our analysis showed individual silver carp condition decreased while their population numbers and biomass increased during their establishment in the Illinois River. Concurrently, analysis of 22 years of producer and consumer abundance and biomass data shows phytoplankton density and macrozooplankton density and biomass decreased—zooplankton by over 90%—during the same period, though the responses of age‐0 native fish biomass and adult native fish biomass were more nuanced. Our study provides compelling evidence of multiple trophic‐level effects from the silver carp invasion in North America and highlights the importance of long‐term data collection and monitoring. Our research shows managers that zooplankton and perhaps phytoplankton are quickly and negatively affected by silver carp, which may eventually cascade into higher trophic levels over longer timescales.

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Large riverine landscapes are among the most productive ecosystems on earth, and the most affected by humans. Few studies explicitly explore the effects of, or responses to, multiple stressors in highly modified large river systems. Changes in fish assemblages in response to multiple anthropogenic stressors were explored from a 60-year data set for the Illinois River (Illinois, USA). Despite a legacy of stressors, the highly modified Illinois River responded to additional multiple stressors, especially four distinct stressor phases, which included two policies to improve water quality and bigheaded carp invasion. The response in fish diversity (Shannon H′) was complex in terms of the number of thresholds in the pattern of fish diversity, the rate and direction of change between thresholds, and the variance of response at two spatial scales and two ecological levels of organization. Overall, nine response trajectories were observed. Changes in fish diversity in the Illinois River since 1959 do not conform to current ecosystem response models. Without long-term and broad-scale data, elucidating complex responses in large river ecosystems is unlikely. Expanding the spatial and temporal scale of investigation in modified large rivers will increase our ability to understand how these ecosystems respond to multiple stressors.

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Understanding the environmental factors that regulate fish recruitment is essential for effective management of fisheries. Generally, first-year survival, and therefore recruitment, is inherently less consistent in systems with high intra-and interannual variability. Irrigation reservoirs display sporadic patterns of annual drawdown, which can pose a substantial challenge to recruitment of fishes. We developed species-specific models using an 18-year data set compiled from state and federal agencies to investigate variables that regulate the recruitment of walleye Sander vitreus and white bass Morone chrysops in irrigation reservoirs in south-west Nebraska, USA. The candidate model set for walleye included only abiotic variables (water-level elevation, minimum daily air temperature during winter prior to hatching, annual precipitation, spring warming rate and May reservoir discharge), and the candidate model set for white bass included primarily biotic variables (catch per unit effort (CPUE) of black crappie Pomoxis nigromaculatus, CPUE of age-0 walleye, CPUE of bluegill Lepomis macrochirus and CPUE of age-3 and older white bass), each of which had a greater relative importance than the single abiotic variable (minimum daily air temperature during winter after hatching). Our findings improve the understanding of the recruitment of fishes in irrigation reservoirs and the relative roles of abiotic and biotic factors.

Declining participation in recreational angling isofgreatconcerntofisherymanagersbecausefishinglicense sales are an important revenue source for protection of aquatic resources.Thisdeclineisfrequentlyattributed,inpart,toincreasedsocietalrelianceonelectronics.Internetusebyanglers isincreasingandfisherymanagersmayusetheInternetasa unique means to increase angler participation. We examined Internet search behavior using Google Insights for Search, a free online tool that summarizes Google searches from 2004 to2011todetermine(1)trendsinInternetsearchvolumefor generalfishing-relatedtermsand(2)therelativeusefulnessof termsrelatedtoanglerrecruitmentprogramsacrosstheUnitedStates.Thoughsearchvolumedeclinedforgeneralfishing terms (e.g., fishing, fishing guide), search volume increased for social media and recruitment terms (e.g., fishing forum, familyfishing)overthe7-yearperiod.Weencouragecoordinatorsofrecruitmentprogramstocapitalizeonanglers'Internet usage by considering Internet search patterns when creating web-based information. Careful selection of terms used in web-based information to match those currently searched by potentialanglersmayhelptodirecttraffictostateagencywebsitesthatsupportrecruitmentefforts.

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Anthropogenic activities have greatly altered the natural flow regime of lotic ecosystems in many ways, including dams and culverts, which restrict sediment transport and fragment fish habitat. Sculpins, Cottus spp., are an important food-web link between macroinvertebrates and larger stream fishes and are greatly affected by culverts. Results from a previous study indicate a substantial increase in the relative abundance of mottled sculpin, Cottus bairdii, was observed upstream of a renovated road-stream crossing during the first season after construction. Redistribution of this nature from a putatively sedentary species would have required substantial movement. Our objectives were to quantify postrestoration mottled sculpin movement and habitat use in a restored stream reach. The extent of post-restoration mottled sculpin movement and habitat use were directly measured using telemetry of Passive Integrated Transponder (PIT) tag-marked fish. The maximum linear distance moved by a marked mottled sculpin was 839 m; 23% of marked mottled sculpin moved .100 m. The number of detections of marked mottled sculpin in each segment was significantly correlated with the amount of small wood (5-10 cm diameter). Increased distribution of mottled sculpin in previously unavailable upstream habitats coupled with substantial post-restoration movement distances provides new insight on their potential for redistribution following habitat reconnection, which is an important consideration for stream restoration projects.