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Metabolic rate is a key parameter in fish energy budgets that strongly influences the output of bioenergetics models. In this study, we tested the hypothesis that metabolic rate varies with growth history of age-1 largemouth bass Micropterus nigricans Cuvier, 1828. Two groups of fish were fed alternating maintenance or ad libitum rations of fathead minnow Pimephales promelas Rafinesque, 1820, so that over a 9-week period, initial and ending size of fish was similar. After 9 weeks, oxygen consumption was measured using static, closed respirometry. Although final body weight was similar between the two groups (means, 104–108 g), specific oxygen consumption for fish fed maintenance rations (0.094 mg O2 g−2 h−1) was 38% less than that measured for fish fed ad libitum (0.152 mg O2 g−2 h−1). Bioenergetics estimates of food consumption were similar to observed values for fish fed ad libitum (∼7% error), but for fish fed maintenance rations, the model overestimated food consumption by 65%. By accounting for changes in metabolic rate owing to reduced feeding, error in model estimates of food consumption was reduced. These findings shed new insight into factors associated with consumption-dependent error in bioenergetics models and highlight the importance of feeding history on metabolic rate of fish. Incorporating growth-dependent metabolism into bioenergetics models can improve model accuracy and allow fisheries biologists to make more informed decisions regarding fish growth and energetics. [ABSTRACT FROM AUTHOR]

Understanding spatial and temporal fluctuations in animal populations remains a central theme in ecology. Here, we investigated the extent of common carp (Cyprinus carpio) recruitment synchrony across North America in relation to a suite of climatic conditions. Common carp were collected from 21 populations up to a linear distance of 2300 km between the most southern and northern locations. Age-frequency histograms were used to estimate year-class strength, and correlation coefficients were used to evaluate synchrony among populations and environmental variables. We then evaluated relationships between common carp recruitment and winter growing degree-days (GDD), summer GDD, precipitation, wind events, and the El Nino Southern Oscillation Index (ENSO). Common carp recruitment was synchronous up to 756 km but asynchronous at larger scales. Winter and summer GDD, precipitation, and wind were also synchronous among locations up to 1640 km apart. Summer GDD appeared most influential to common carp recruitment but varied across latitudes, with negative effects identified at low latitudes and positive effects identified at higher latitudes. Our results provide new insights into the spatial scale of recruitment synchrony of a non-native freshwater fish and indicate that climatic conditions at local to regional scales likely influence recruitment patterns. La comprehension des fluctuations spatiales et temporelles dans les populations animales constitue un theme central en ecologie. Nous examinons l'ampleur du synchronisme du recrutement de carpes communes (Cyprinus carpio) en Amerique du Nord par rapport a une serie de conditions climatiques. Des carpes communes ont ete prelevees de 21 populations separees par des distances lineaires allant jusqu'a 2300 km. Des histogrammes de la frequence selon l'age ont ete utilises pour estimer la force des classes d'age et des coefficients de correlation ont ete utilises pour evaluer le synchronisme entre les populations et en fonction de variables environnementales. Nous avons ensuite evalue les relations entre le recrutement de carpes communes et les degres-jours de croissance (DJC) hivernaux et estivaux, les precipitations, les episodes venteux et l'indice El Nino oscillation australe (ENSO). Le recrutement de carpes communes est synchrone jusqu'a une distance de 756 km, mais asynchrone a plus grande echelle. Les DJC hivernaux et estivaux, les precipitations et les vents sont egalement synchrones entre des sites distants de jusqu'a 1640 km. Les DJC estivaux semblent exercer la plus grande influence sur le recrutement des carpes, mais varient selon la latitude, des effets negatifs ayant ete notes a basse latitude et des effets positifs, a plus haute latitude. Nos resultats fournissent de nouveaux renseignements sur l'echelle spatiale du synchronisme du recrutement d'un poisson d'eau douce non indigene et indiquent que les conditions climatiques aux echelles locales a regionales influencent vraisemblablement les motifs de recrutement. [Traduit par la Redaction], Introduction Understanding the mechanisms regulating variability in animal population dynamics is an important aspect of ecology. Animal populations commonly fluctuate both spatially and temporally (Glazier 1986; Pimm and Redfearn 1988), [...]

To examine agricultural impacts on stream food webs, we used gut content analysis (GCA) and stable isotope analysis (SIA) to investigate the influence of riparian forest buffers on the diet and trophic position of five stream fish species in a row‐crop agricultural watershed. Six study streams were divided into two categories (forested and agricultural) based on percentages of riparian forest and agriculture in the watershed. Results suggest alterations in riparian vegetation (forested vs. cropland) had strong impacts on instream characteristics and basal resources that affected prey abundances and fish trophic structure. Although differences varied among species, GCA revealed fish in forested streams had a more diverse diet that included greater numbers of terrestrial invertebrates and aquatic invertebrate predators, whereas fish in agricultural streams consumed more aquatic herbivores and decapods. Diet shifts of the omnivorous creek chub followed differences in basal resource biomass, with greater proportions of algae consumed in agricultural sites contrasted by greater detritus consumed in forested sites. SIA Bayesian mixing‐model results supported diet differences shown by GCA, including higher contributions of terrestrial invertebrates to fish diets in forested streams. However, the isotopic overlap of aquatic invertebrates in agricultural streams limited diet contribution comparisons. SIA indicated fish trophic position was higher in forested than agricultural streams for all species, but GCA was required to identify that greater consumption of predatory prey likely caused this widespread change in fish trophic structure. Results highlight the benefits of integrating SIA and GCA and the importance of riparian forests to stream fishes in agricultural watersheds. [ABSTRACT FROM AUTHOR]

The relationship between the magnitude of reproduction and adult density of pelagically spawning carp (PSC) species (bigheaded carp Hypophthalmichthys spp., Grass Carp Ctenopharyngodon idella, and Black Carp Mylopharyngodon piceus) and the influence of environmental factors on this relationship are valuable information for management and control of these highly invasive cyprinids. Six years of standardized monitoring for PSC reproduction and adult density in navigation pools of the Illinois Waterway (IWW; the Illinois River and its connection to Lake Michigan through the Des Plaines River and Chicago Area Waterway System), in conjunction with removal efforts in the upper IWW, where there is limited fish movement between pools, provided an opportunity to deepen our understanding of factors affecting the reproductive productivity of this invasive assemblage. Reproductive activity most commonly occurred in May and June, with the magnitude of reproduction in June far exceeding that occurring in other months. The highest egg counts were found within a 72‐km zone containing the hydromorphological transition between the upper and lower Illinois River, with the majority of PSC larval drift occurring below this zone in the lower Illinois River. Magnitude of reproduction increased nonlinearly with adult PSC density, declining at high adult densities. Annual egg counts were also higher in years that combined more variable spring discharge with higher accumulated degree‐days through June. The density‐dependent reproduction exhibited by PSC implies that any stock–recruitment variation observed for these species needs to be interpreted cautiously before being ascribed to environmental factors affecting survival from hatching to juvenile stages. An increased understanding of which life stages of PSC are subject to density dependence can refine projections of how these species respond to harvest and other control measures. [ABSTRACT FROM AUTHOR]

Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis, collectively known as bigheaded carps (BHC), are invasive fishes in the Mississippi River and surrounding basins. Increasing evidence suggests harmful impacts of BHC on native fisheries (e.g., competition). Monitoring the abundance of BHC is difficult with traditional fisheries gears, and few studies have evaluated early life stage sampling. Identifying the spawning locations of BHC through early life stage sampling has the ability to enhance management efforts by applying focus to areas that have potential to serve as population sources. We evaluated the performance of three gears in sampling larval BHC and native taxa within large‐river tributaries in terms of abundance, community assemblage, and size structure. We sampled ichthyoplankton in tributaries with active (push net) and passive (drift net, light trap) gears from March through September 2016. Relative abundance of BHC was greatest in push nets followed by drift nets and was lowest in light traps. Native cyprinids and catostomids as well as BHC comprised a large portion of the total catch. Environmental and habitat characteristics (stream velocity, dissolved oxygen, and temperature) related to BHC reproduction influenced each gear's ability to capture larval BHC, although relationships in final models were not significant. Taxonomic size selectivity existed among gears; in particular, larger BHC were collected in push nets relative to the other gears. Push nets were the most effective in sampling BHC, and remaining gears exhibited unique strengths. Although less effective than active push nets, drift nets proved useful for monitoring BHC in tributaries and may be advantageous in shallow systems with adequate flow. Light traps were ineffective at capturing BHC larvae in tributaries but may offer utility in lentic habitats or for native cyprinids. Our comparison serves as a guide for monitoring larval BHC in their invaded range and for detection in new areas, such as tributaries of the Great Lakes. [ABSTRACT FROM AUTHOR]