Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications Copyright (c) 2013 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/ncfwrustaff Recent documents in Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications en-us Fri, 01 Mar 2013 01:47:25 PST 3600 Passive Capture Techniques http://digitalcommons.unl.edu/ncfwrustaff/111 http://digitalcommons.unl.edu/ncfwrustaff/111 Wed, 27 Feb 2013 14:02:38 PST Passive capture techniques involve the capture of fishes or other aquatic animals by entanglement, entrapment, or angling devices that are not actively moved by humans or machines while the organisms are being captured (Lagler 1978). The behavior and movements of the animals themselves result in their capture. The techniques used in passive sampling of fish populations are similar to those used for food gathering over the centuries. Nets and traps have been widely used among various cultures, and many of the currently applied techniques were used by the ancient Egyptians, Greeks, and Romans (Alverson 1963).

Based on their mode of capture, passive sampling devices can be divided into three groups: (1) entanglement, (2) entrapment, and (3) angling gears. Entanglement devices capture fish by holding them ensnared or tangled in webbing or mesh made of natural or artificial materials. Gill nets and trammel nets are examples of entanglement gears (Figure 6.1). Entrapment devices capture organisms that enter an enclosed area through one or more funnel- or V-shaped openings that hinder escape after entrance. Hoop nets, trap nets, and pot devices are examples of entrapment gears (Figures 6.2 and 6.3). Angling devices capture fish with a baited hook and line. Trotlines and longlines are examples of passive angling gears (Figure 6.4).

Gear selectivity and gear efficiency are important considerations with respect to passive sampling devices. Often these terms are used interchangeably, but they have different, specific definitions. Gear selectivity is the bias of a sample obtained with a given gear (Box 6.1). Selectivity for species, sizes, and sexes of fishes occurs in samples taken with specific types of gear. Species selectivity refers to overrepresentation of particular species in samples as compared with the assemblage of species present. Similarly, size or sex selectivity refers to overrepresentation of specific sizes (lengths) or one sex within samples from a fish population. Fisheries scientists may use gear selectivity to their benefit when targeting specific species or sizes of fishes, thereby enhancing their sampling efficiency. The efficiency of a gear refers to the amount of effort expended to capture target organisms (Box 6.2). It is generally desirable to maximize the efficiency of a sampling gear to save time and money in single-species assessments of fisheries. Even with efficient sampling gear, the sampling effort needed to estimate the relative abundance and other descriptive statistics for a given species may be unrealistic (Gerow 2007).

]]> Wayne A. Hubert et al. Are Agrofuels A Conservation Threat Or Opportunity For Grassland Birds In The United States? http://digitalcommons.unl.edu/ncfwrustaff/110 http://digitalcommons.unl.edu/ncfwrustaff/110 Tue, 29 Jan 2013 09:31:26 PST In the United States, government-mandated growth in the production of crops dedicated to biofuel (agrofuels) is predicted to increase the demands on existing agricultural lands, potentially threatening the persistence of populations of grassland birds they support. We review recently published literature and datasets to (1) examine the ability of alternative agrofuel crops and their management regimes to provide habitat for grassland birds, (2) determine how crop placement in agricultural landscapes and agrofuel-related land-use change will affect grassland birds, and (3) identify critical research and policy-development needs associated with agrofuel production. We find that native perennial plants proposed as feedstock for agrofuel (switchgrass, Panicum virgatum, and mixed grass–forb prairie) have considerable potential to provide new habitat to a wide range of grassland birds, including rare and threatened species. However, industrialization of agrofuel production that maximizes biomass, homogenizes vegetation structure, and results in the cultivation of small fields within largely forested landscapes is likely to reduce species richness and/or abundance of grassland-dependent birds. Realizing the potential benefits of agrofuel production for grassland birds’ conservation will require the development of new policies that encourage agricultural practices specifically targeting the needs of grassland specialists. The broad array of grower-incentive programs in existence may deliver new agrofuel policies effectively but will require coordination at a spatial scale broader than currently practiced, preferably within an adaptive-management framework.

]]> Bruce A. Robertson et al. Nest Predation And Circulating Corticosterone Levels Within And Among Species http://digitalcommons.unl.edu/ncfwrustaff/109 http://digitalcommons.unl.edu/ncfwrustaff/109 Tue, 29 Jan 2013 09:22:22 PST Variation in the risk of predation to offspring can influence the expression of reproductive strategies both within and among species. Appropriate expression of reproductive strategies in environments that differ in predation risk can have clear advantages for fitness. Although adult-predation risk appears to influence glucocorticosteroid levels, leading to changes in behavioral and life-history strategies, the influence of offspring-predation risk on adult glucocorticosteroid levels remains unclear. We compared total baseline corticosterone concentrations in Gray-headed Juncos (Junco hyemalis dorsalis) nesting on plots with and without experimentally reduced risk of nest predation. Despite differences in risk between treatments, we failed to find differences in total baseline corticosterone concentrations. When we examined corticosterone concentrations across a suite of sympatric species, however, higher risk of nest predation correlated with higher total baseline corticosterone levels. As found previously, total baseline corticosterone was negatively correlated with body condition and positively correlated with date of sampling. However, we also found that corticosterone levels increased seasonally, independent of stage of breeding. Nest predation can alter the expression of birds’ reproductive strategies, but our findings suggest that total baseline corticosterone is not the physiological mechanism regulating these responses.

]]> Joseph J. Fontaine et al. Land Use, Landscapes, and Biological Invasions http://digitalcommons.unl.edu/ncfwrustaff/108 http://digitalcommons.unl.edu/ncfwrustaff/108 Tue, 29 Jan 2013 09:12:47 PST The negative effect of invasive species on native species, communities, and ecosystems is widely recognized, and the economic effects in the United States are estimated to be billions of dollars annually. Studies often examine traits of nonnative species or examine what makes a particular habitat invasible. To better understand the factors governing invasions, we used the flora of Nebraska to characterize and compare native and nonnative plant occurrences throughout the state. In addition, we assessed four critical landscape predictors of nonnative plant richness: human population size and three land cover attributes that included percentage of grassland, percentage of agriculture, and percentage of public lands. Results indicated that individual plant species richness has increased by about 35% through invasions (primarily of annuals from the family Poaceae). In addition, human population density, percentage of agriculture, and percentage of public lands all show a positive association with nonnative plant richness. Successful plant invasions may change the composition of species communities, basic ecological functions, and the delivery of ecosystem services. Thus, identifying the factors that influence such variation in distribution patterns can be fundamental to recognizing the present and potential future extent of nonnative plant infestations and, in turn, developing appropriate management programs.

]]> Karie L. Decker et al. Insight on Invasions and Resilience Derived from Spatiotemporal Discontinuities of Biomass at Local and Regional Scales http://digitalcommons.unl.edu/ncfwrustaff/107 http://digitalcommons.unl.edu/ncfwrustaff/107 Wed, 23 Jan 2013 12:14:05 PST Understanding the social and ecological consequences of species invasions is complicated by nonlinearities in processes, and differences in process and structure as scale is changed. Here we use discontinuity analyses to investigate nonlinear patterns in the distribution of biomass of an invasive nuisance species that could indicate scale-specific organization. We analyze biomass patterns in the flagellate Gonyostomum semen (Raphidophyta) in 75 boreal lakes during an 11-year period (1997-2007). With simulations using a unimodal null model and cluster analysis, we identified regional groupings of lakes based on their biomass patterns. We evaluated the variability of membership of individual lakes in regional biomass groups. Temporal trends in local and regional discontinuity patterns were analyzed using regressions and correlations with environmental variables that characterize nutrient conditions, acidity status, temperature variability, and water clarity. Regionally, there was a significant increase in the number of biomass groups over time, indicative of an increased number of scales at which algal biomass organizes across lakes. This increased complexity correlated with the invasion history of G. semen and broad-scale environmental change (recovery from acidification). Locally, no consistent patterns of lake membership to regional biomass groups were observed, and correlations with environmental variables were lake specific. The increased complexity of regional biomass patterns suggests that processes that act within or between scales reinforce the presence of G. semen and its potential to develop high-biomass blooms in boreal lakes. Emergent regional patterns combined with locally stochastic dynamics suggest a bleak future for managing G. semen, and more generally why invasive species can be ecologically successful.

]]> David G. Angeler et al. Species, Functional Groups, and Thresholds in Ecological Resilience http://digitalcommons.unl.edu/ncfwrustaff/106 http://digitalcommons.unl.edu/ncfwrustaff/106 Wed, 23 Jan 2013 12:07:08 PST The cross-scale resilience model states that ecological resilience is generated in part from the distribution of functions within and across scales in a system. Resilience is a measure of a system’s ability to remain organized around a particular set of mutually reinforcing processes and structures, known as a regime. We define scale as the geographic extent over which a process operates and the frequency with which a process occurs. Species can be categorized into functional groups that are a link between ecosystem processes and structures and ecological resilience. We applied the cross-scale resilience model to avian species in a grassland ecosystem. A species’ morphology is shaped in part by its interaction with ecological structure and pattern, so animal body mass reflects the spatial and temporal distribution of resources. We used the logtransformed rank-ordered body masses of breeding birds associated with grasslands to identify aggregations and discontinuities in the distribution of those body masses. We assessed cross-scale resilience on the basis of 3 metrics: overall number of functional groups, number of functional groups within an aggregation, and the redundancy of functional groups across aggregations. We assessed how the loss of threatened species would affect cross-scale resilience by removing threatened species from the data set and recalculating values of the 3 metrics. We also determined whether more function was retained than expected after the loss of threatened species by comparing observed loss with simulated random loss in a Monte Carlo process. The observed distribution of function compared with the random simulated loss of function indicated that more functionality in the observed data set was retained than expected. On the basis of our results, we believe an ecosystem with a full complement of species can sustain considerable species losses without affecting the distribution of functions within and across aggregations, although ecological resilience is reduced. We propose that the mechanisms responsible for shaping discontinuous distributions of body mass and the nonrandom distribution of functions may also shape species losses such that local extinctions will be nonrandom with respect to the retention and distribution of functions and that the distribution of function within and across aggregations will be conserved despite extinctions.

El modelo de resiliencia transescala establece que la resiliencia ecológica se genera en parte por la distribución de funciones dentro y a través de escalas en el sistema. La resiliencia es una medida de la habilidad de un sistema para permanecer organizado en torno a un conjunto determinado de procesos y estructuras mutuamente reforzadoras, conocido como régimen. Definimos escala como la extensión geográfica en la cual opera un proceso y la frecuencia con que ocurre. Las especies se pueden clasificar en grupos funcionales que son un vínculo entre los procesos del ecosistema y la resiliencia ecológica. Aplicamos el modelo de resiliencia transescala a especies de aves en un ecosistema de pastizal. La morfología de una especies esta determinada en parte por su interacción con la estructura y patrón ecológico, de tal modo que la masa corporal de un animal refleja la distribución espacial y temporal de los recursos. Utilizamos la masa corporal, ordenada por rangos y transformada logarítmicamente, de aves asociadas a pastizales para identificar agregaciones y discontinuidades en la distribución de esas masas corporales. Evaluamos la resiliencia transescalar con base en 3 medidas: n´umero total de grupos funcionales, n´umero de grupos funcionales dentro de una agregación, y la redundancia de grupos funcionales en las agregaciones. Evaluamos el efecto de la pérdida de especies amenazadas sobre la resiliencia transescalar mediante la remoción de especies amenazadas del conjunto de datos y el nuevo cálculos de las 3 medidas. También determinamos si se retenía más función que lo esperado después de la pérdida de especies amenazadas mediante la comparación de la pérdida observada con la pérdida aleatoria simulada en un proceso Monte Carlo. La distribución observada de la función comparada con la pérdida aleatoria simulada indicó que se retenía mas funcionalidad que la esperada en el conjunto de datos observados. Con base en nuestros resultados, consideramos que un ecosistema con un complemento completo de especies puede sustentar considerables pérdidas de especies sin que se afecte la distribución de funciones dentro y entre agregaciones, aunque la resiliencia ecológica se reduce. Proponemos que los mecanismos responsables de moldear las distribuciones discontinuas de la masa corporal y la distribución no aleatoria de funciones también puede moldear la pérdida de especies, como extinciones locales, serán no aleatorios con respecto a la retención y distribución de funciones y que la distribución de la función dentro y entre agregaciones se conservará no obstante las extinciones.

]]> Shana M. Sundstrom et al. Latitudinal Influence on Age Estimates Derived from Scales and Otoliths for Bluegills http://digitalcommons.unl.edu/ncfwrustaff/105 http://digitalcommons.unl.edu/ncfwrustaff/105 Mon, 12 Nov 2012 08:27:22 PST Scales are perceived to give reliable estimates of age of fish in northern latitudes and unreliable estimates of age in southern latitudes, whereas otoliths are perceived to give reliable estimates of age regardless of latitude. The objective of our study was to assess the influence of latitude on the estimates of ages derived from scales and otoliths for bluegill Lepomis macrochirus. Our hypothesis was that a south-to-north gradient exists for precision between scales and otoliths with partial agreement between age estimates derived from scales and otoliths for fish in southern latitudes and nearly complete agreement between age estimates derived from scales and otoliths for fish in northern latitudes. Fish were sampled from Louisiana (latitude = 30º43'48''N) to North Dakota (latitude = 47º05'49''N). Contrary to a priori expectations, we did not find greater agreement in age estimates between structures in northern bluegill stocks than in those in the southern USA. The low agreement between structures increases uncertainty in the source of aging error, given that both scales and otoliths are valid structures (i.e., age estimates validated as accurate) for estimating ages of bluegills. Biologists should not compare age-dependent parameters for bluegill populations derived from different aging structures.

]]> Lucas K. Kowalewski et al. Population estimate of Chinese mystery snail (<i>Bellamya chinensis</i>) in a Nebraska reservoir http://digitalcommons.unl.edu/ncfwrustaff/104 http://digitalcommons.unl.edu/ncfwrustaff/104 Mon, 12 Nov 2012 08:13:53 PST The Chinese mystery snail (Bellamya chinensis) is an aquatic invasive species in North America. Little is known regarding this species’ impacts on freshwater ecosystems. It is believed that population densities can be high, yet no population estimates have been reported. We utilized a mark-recapture approach to generate a population estimate for Chinese mystery snail in Wild Plum Lake, a 6.47-ha reservoir in southeast Nebraska. We calculated, using bias-adjusted Lincoln-Petersen estimation, that there were approximately 664 adult snails within a 127 m2 transect (5.2 snails/m2). If this density was consistent throughout the littoral zone (<3 m in depth) of the reservoir, then the total adult population in this impoundment is estimated to be 253,570 snails, and the total Chinese mystery snail wet biomass is estimated to be 3,119 kg (643 kg/ha). If this density is confined to the depth sampled in this study (1.46 m), then the adult population is estimated to be 169,400 snails, and wet biomass is estimated to be 2,084 kg (643 kg/ha). Additional research is warranted to further test the utility of mark-recapture methods for aquatic snails and to better understand Chinese mystery snail distributions within reservoirs.

]]> Noelle M. Chaine et al. Woody Invasions of Urban Trails and the Changing Face of Urban Forests in the Great Plains, USA http://digitalcommons.unl.edu/ncfwrustaff/103 http://digitalcommons.unl.edu/ncfwrustaff/103 Thu, 18 Oct 2012 13:47:00 PDT Corridors such as roads and trails can facilitate invasions by non-native plant species. The open, disturbed habitat associated with corridors provides favorable growing conditions for many non-native plant species. Bike trails are a corridor system common to many urban areas that have not been studied for their potential role in plant invasions. We sampled five linear segments of urban forest along bike trails in Lincoln, Nebraska to assess the invasion of woody non-native species relative to corridors and to assess the composition of these urban forests. The most abundant plant species were generally native species, but five non-native species were also present: white mulberry (Morus alba), common buckthorn (Rhamnus cathartica), tree-of-heaven (Ailanthus altissima), honeysuckle (Lonicera spp.) and elm (Ulmus spp.). The distribution of two of the woody species sampled, common buckthorn and honeysuckle, significantly decreased with increasing distance from a source patch of vegetation (P = 0.031 and 0.030). These linear habitats are being invaded by non-native tree and shrub species, which may change the structure of these urban forest corridors. If nonnative woody plant species become abundant in the future, they may homogenize the plant community and reduce native biodiversity in these areas.

]]> Kristine T. Nemec et al. Using the Internet to Understand Angler Behavior in the Information Age http://digitalcommons.unl.edu/ncfwrustaff/102 http://digitalcommons.unl.edu/ncfwrustaff/102 Thu, 18 Oct 2012 13:37:54 PDT Declining participation in recreational angling is of great concern to fishery managers because fishing license sales are an important revenue source for protection of aquatic resources. This decline is frequently attributed, in part, to increased societal reliance on electronics. Internet use by anglers is increasing and fishery managers may use the Internet as a 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 to 2011 to determine (1) trends in Internet search volume for general fishing-related terms and (2) the relative usefulness of terms related to angler recruitment programs across the United States. Though search volume declined for general fishing terms (e.g., fishing, fishing guide), search volume increased for social media and recruitment terms (e.g., fishing forum, family fishing) over the 7-year period. We encourage coordinators of recruitment programs to capitalize on anglers’ 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 potential anglers may help to direct traffic to state agency websites that support recruitment efforts.

]]> Dustin R. Martin et al. Predictions and retrodictions of the hierarchical representation of habitat in heterogeneous environments http://digitalcommons.unl.edu/ncfwrustaff/101 http://digitalcommons.unl.edu/ncfwrustaff/101 Wed, 11 Jul 2012 09:23:17 PDT Interaction between habitat and species is central in ecology. Habitat structure may be conceived as being hierarchical, where larger, more diverse, portions or categories contain smaller, more homogeneous portions. When this conceptualization is combined with the observation that species have different abilities to relate to portions of the habitat that differ in their characteristics, a number of known patterns can be derived and new patterns hypothesized. We propose a quantitative form of this habitat–species relationship by considering species abundance to be a function of habitat specialization, habitat fragmentation, amount of habitat, and adult body mass. The model reproduces and explains patterns such as variation in rank–abundance curves, greater variation and extinction probabilities of habitat specialists, discontinuities in traits (abundance, ecological range, pattern of variation, body size) among species sharing a community or area, and triangular distribution of body sizes, among others. The model has affinities to Holling’s textural discontinuity hypothesis and metacommunity theory but differs from both by offering a more general perspective. In support of the model, we illustrate its general potential to capture and explain several empirical observations that historically have been treated independently.

]]> Jurek Kolasa et al. Habitat selection by adult walleye during spawning season in irrigation reservoirs: A patch occupancy modeling approach http://digitalcommons.unl.edu/ncfwrustaff/100 http://digitalcommons.unl.edu/ncfwrustaff/100 Wed, 11 Jul 2012 09:05:28 PDT Recruitment of walleye (Sander vitreus Mitchill) is limited in irrigation reservoirs of the Republican River basin in southwestern Nebraska. The causal mechanism for this limited recruitment is unknown, but may be related to a lack of suitable spawning habitat. Patch occupancy models were developed to describe variation in detection probability and habitat selection during spawning season using shoreline electrofishing data. Detection of adult walleye was negatively affected by water temperature, silt substrate, and woody cover. Adult walleye selected sites with cooler water temperatures and greater fetch at Enders Reservoir, and large rock substrate and no cover at Hugh Butler Lake; these characteristics are limited to areas on or near the riprap dams in both reservoirs. Walleye eggs were also only found in these areas. We conclude that patch occupancy modeling provided valuable information when considering habitat improvement projects and propose a management approach for the addition of walleye spawning habitat in irrigation reservoirs.

]]> Dustin R. Martin et al. Land Use, Landscapes, and Biological Invasions http://digitalcommons.unl.edu/ncfwrustaff/99 http://digitalcommons.unl.edu/ncfwrustaff/99 Wed, 25 Apr 2012 10:59:52 PDT The negative effect of invasive species on native species, communities, and ecosystems is widely recognized, and the economic effects in the United States are estimated to be billions of dollars annually. Studies often examine traits of nonnative species or examine what makes a particular habitat invasible. To better understand the factors governing invasions, we used the flora of Nebraska to characterize and compare native and nonnative plant occurrences throughout the state. In addition, we assessed four critical landscape predictors of nonnative plant richness: human population size and three land cover attributes that included percentage of grassland, percentage of agriculture, and percentage of public lands. Results indicated that individual plant species richness has increased by about 35% through invasions (primarily of annuals from the family Poaceae). In addition, human population density, percentage of agriculture, and percentage of public lands all show a positive association with nonnative plant richness. Successful plant invasions may change the composition of species communities, basic ecological functions, and the delivery of ecosystem services. Thus, identifying the factors that influence such variation in distribution patterns can be fundamental to recognizing the present and potential future extent of nonnative plant infestations and, in turn, developing appropriate management programs.

]]> Karie L. Decker et al. Nest predation, food, and female age explain seasonal declines in clutch size http://digitalcommons.unl.edu/ncfwrustaff/98 http://digitalcommons.unl.edu/ncfwrustaff/98 Wed, 25 Apr 2012 10:54:05 PDT The selection pressures responsible for intra- and interspecific variation in avian clutch size have been debated for over half a century. Seasonal declines in clutch size represent one of the most robust patterns in avian systems, yet despite extensive research on the subject, the mechanisms underlying this pattern remain largely unknown. We tested a combination of experimental and observational predictions to evaluate ten hypotheses, representing both evolutionary and proximate mechanisms proposed to explain seasonal declines in avian clutch size. In line with long held life-history theory, we found strong support for both an evolved and proximate response to food availability for young. We also found evidence consistent with predictions that proximate level experiential nest predation influences seasonal declines in clutch size. Finally, older females appear to invest more in reproduction (initiate nests earlier and lay larger clutches) and choose better territories than younger females. Our results highlight the importance of examining multiple hypotheses in a theoretical context to elucidate the ecological processes underlying commonly observed patterns in life history.

]]> Karie L. Decker et al. Using consumption rate to assess potential predators for biological control of white perch http://digitalcommons.unl.edu/ncfwrustaff/97 http://digitalcommons.unl.edu/ncfwrustaff/97 Fri, 23 Sep 2011 08:47:00 PDT Control of undesirable fishes is important in aquatic systems, and using predation as a tool for biological control is an attractive option to fishery biologists. However, determining the appropriate predators for biological control is critical for success. The objective of this study was to evaluate the utility of consumption rate as an index to determine the most effective predators for biological control of an invasive fish. Consumption rate values were calculated for nine potential predators that prey on white perch Morone americana in Branched Oak and Pawnee reservoirs, Nebraska. The consumption rate index provided a unique and insightful means of determining the potential effectiveness of each predator species in controlling white perch. Cumulative frequency distributions facilitated interpretation by providing a graphical presentation of consumption rates by all individuals within each predator species. Largemouth bass Micropterus salmoides, walleye Sander vitreus and sauger S. canadensis were the most efficient white perch predators in both reservoirs; however, previous attempts to increase biomass of these predators have failed suggesting that successful biological control is unlikely using existing predator species in these Nebraska reservoirs.

Le contrôle des poissons indésirables est important dans les écosystèmes aquatiques et l’utilisation de la prédation comme outil de contrôle biologique est une option attractive pour les biologistes des pêches. Toutefois, déterminer les bons prédateurs pour un contrôle biologique est crucial pour sa réussite. L’objectif de cette étude a été de tester l’utilité du taux de consommation comme indice de détermination des prédateurs les plus appropriés pour le contrôle biologique d’un poisson invasif. Les valeurs du taux de consommation ont été calculées pour neuf prédateurs potentiels de la perche blanche Morone americana dans les réservoirs Branched Oak et Pawnee, Nébraska. L’indice du taux de consommation est un moyen unique et perspicace pour déterminer l’effectivité potentielle de chaque espèce de prédateur dans le contrôle de la perche blanche. Les distributions de fréquences cumulées facilitent l’interprétation en donnant une représentation graphique des taux de consommation par tous les individus d’une même espèce de prédateur. Le bass à grande bouche Micropterus salmoides, les sandres Sander vitreus et S. canadensis sont les prédateurs les plus efficaces de la perche blanche dans les deux réservoirs. Toutefois des tentatives antérieures pour augmenter la biomasse de ces prédateurs n’ont pas réussi, suggérant que le contrôle biologique est improbable avec les espèces de prédateurs présentes dans ces réservoirs du Nébraska.

]]> Nathan J.C. Gosch et al. Catch of Channel Catfish with Tandem-Set Hoop Nets and Gill Nets in Lentic Systems of Nebraska http://digitalcommons.unl.edu/ncfwrustaff/96 http://digitalcommons.unl.edu/ncfwrustaff/96 Tue, 13 Sep 2011 11:53:46 PDT Twenty-six Nebraska water bodies representing two ecosystem types (small standing waters and large standing waters) were surveyed during 2008 and 2009 with tandem-set hoop nets and experimental gill nets to determine if similar trends existed in catch rates and size structures of channel catfish Ictalurus punctatus captured with these gears. Gear effi ciency was assessed as the number of sets (nets) that would be required to capture 100 channel catfish given observed catch per unit effort (CPUE). Efficiency of gill nets was not correlated with effi ciency of hoop nets for capturing channel catfish. Small sample sizes prohibited estimation of proportional size distributions in most surveys; in the four surveys for which sample size was sufficient to quantify length-frequency distributions of captured channel catfish, distributions differed between gears. The CPUE of channel catfi sh did not differ between small and large water bodies for either gear. While catch rates of hoop nets were lower than rates recorded in previous studies, this gear was more efficient than gill nets at capturing channel catfish. However, comparisons of size structure between gears may be problematic.

]]> Lindsey K. Richters et al. Influence of Throat Configuration and Fish Density on Escapement of Channel Catfish from Hoop Nets http://digitalcommons.unl.edu/ncfwrustaff/95 http://digitalcommons.unl.edu/ncfwrustaff/95 Tue, 13 Sep 2011 11:48:46 PDT In recent years, several state agencies have adopted the use of baited, tandemset hoop nets to assess lentic channel catfish Ictalurus punctatus populations. Some level of escapement from the net is expected because an opening exists in each throat of the net, although factors infl uencing rates of escapement from hoop nets have not been quantified. We conducted experiments to quantify rates of escapement and to determine the infl uence of throat configuration and fish density within the net on escapement rates. An initial experiment to determine the rate of escapement from each net compartment utilized individually tagged channel catfish placed within the entrance (between the two throats) and cod (within the second throat) compartments of a single hoop net for overnight sets. From this experiment, the mean rate (±SE) of channel catfish escaping was 4.2% (±1.5) from the cod (cod throat was additionally restricted from the traditionally manufactured product), and 74% (±4.2) from the entrance compartments. In a subsequent experiment, channel catfish were placed only in the cod compartment with different throat configurations (restricted or unrestricted) and at two densities (low [6 fish per net] and high [60 fish per net]) for overnight sets to determine the infl uence of fish density and throat configuration on escapement rates. Escapement rates between throat configurations were doubled at low fish density (13.3 ± 5.4% restricted versus 26.7 ± 5.6% unrestricted) and tripled at high fish density (14.3 ± 4.9% restricted versus 51.9 ± 5.0% unrestricted). These results suggest that retention efficiency is high from cod compartments with restricted throat entrances. However, managers and researchers need to be aware that modification to the cod throats (restrictions) is needed for hoop nets ordered from manufacturers. Managers need to be consistent in their use and reporting of cod end throat configurations when using this gear.

]]> Mark T. Porath et al. Status of the Common Snook (<i>Centropomus undecimalis</i>) in Texas http://digitalcommons.unl.edu/ncfwrustaff/94 http://digitalcommons.unl.edu/ncfwrustaff/94 Mon, 11 Apr 2011 14:03:58 PDT Catch data are summarized for common snook (Centropomus undecimalis) from 1975 through 2004 from the lower Laguna Madre, the only area along the Texas coast where common snook are routinely captured. Catch rates of common snook were low < 1 common snook per gill net set) and varied among years, as did size structure. Based on the catch rate and size structure data, the adult common snook population is characterized by low abundance and erratic recruitment (i.e., missing or extremely weak year-classes are common). Additional comments on the status of common snook in Texas are provided.

]]> Kevin L. Pope et al. Avian Conservation in the Prairie Pothole Region, Northern Great Plains: Understanding the Links between Climate, Ecosystem Processes, Wetland Management, and Bird Communities http://digitalcommons.unl.edu/ncfwrustaff/93 http://digitalcommons.unl.edu/ncfwrustaff/93 Fri, 18 Mar 2011 12:35:49 PDT Historically, the Prairie Pothole Region (PPR) of North America was characterized by myriad semi-permanent, seasonal, and temporary wetlands interspersed among rivers in a context of prairie uplands. These wetlands have supported millions of en route and breeding wetland-dependent birds. Today, expanses of the PPR landscape are dominated by intensive agriculture, and many of the remaining habitats have been impacted by altered water regimes, increasing sedimentation, and changes in plant communities. Climate change is likely to cause further alterations by shifting the seasonal availability and distribution of water and vegetation communities. Climate change will also affect the phenology (annual recurrence of phenomena) of vegetation green-up, seed production, and insect emergence. In concert, these changes could alter the capacity of PPR habitats to support waterbirds. Consequently, natural-resource managers and conservation planners in the PPR have an immediate need for effective tools that can evaluate the effects these changes would have on wetland-dependent bird communities.

To that end, a team of U.S. Geological Survey (USGS) scientists and cooperators with expertise in the sciences of climate, hydrology, and ecology has convened to address the potential impacts of climate change on wetland-dependent bird species in the PPR. This team is developing a set of products, including: (1) a synthesis of current knowledge on the interrelationships of climate, wetlands condition, and bird communities; and (2) data on historical and future projections of climate (these projections will be formatted for use in standard mapping software). We will develop models to: (1) forecast effects and biological outcomes of climate change on water quality and quantity in wetlands and riverine ecosystems of the PPR; (2) elucidate relationships between climate, streamflow, water management, and wetland plants; and (3) understand and forecast bird responses to changing habitat conditions and to the timing of resource availability. The outcomes of this research will inform and assist managers and conservation professionals tasked with conserving populations of wetland-dependent birds.

]]> Susan K. Skagen et al. Yellow Jackets May Be An Underestimated Component Of An Ant-Seed Mutualism http://digitalcommons.unl.edu/ncfwrustaff/92 http://digitalcommons.unl.edu/ncfwrustaff/92 Thu, 03 Mar 2011 11:39:04 PST Yellow jackets (Hymenoptera: Vespidae) are attracted to the typically ant-dispersed seeds of trilliums and will take seeds from ants in the genus Aphaeogaster. To determine if yellow jacket, Vespulla maculifrons (Buysson), presence interferes with seed foraging by ants, we presented seeds of Trillium discolor Wray to three species (A. texana carolinesis Wheeler, Formica schaufussi Mayr, and Solenopsis invicta Buren) of seed-carrying ants in areas where vespids were present or excluded. We found that interspecific aggression between yellow jackets and ants is species specific. Vespid presence decreased average foraging time and increased foraging efficiency of two of the three ant species studied, a situation that might reflect competition for a limited food source. We also found that yellow jackets removed more seeds than ants, suggestive that vespids are important, albeit underestimated, components of ant-seed mutualisms.

]]> Megan T. Bale et al.