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MDFRC item.1. One of the greatest threats to lotic ecosystems is flow regulation. The impacts of flow regulation on native fish are often mitigated using periodic water allocations, termed environmental flows. The effectiveness of environmental flows has been studied in some systems, but the role of flow conditions prior to water allocation (i.e. antecedent conditions) has rarely been quantified. 2. We evaluated the effects of floodplain inundation due to variable river flows on fish abundance in wetlands of the mid-Murray River, Australia, using a hierarchical multi-species model parameterized to estimate fish abundance while accounting for variable detection. We evaluated the effects of antecedent conditions on three time-scales, including patterns in long-term (5 years prior), medium-term (1 year prior) and short-term (3 months prior) wetland inundations. 3. While species-specific responses to antecedent conditions varied, we found a general divergence in the responses of native and non-native species. Native fish tended to respond positively to consistent frequent inundation of wetlands, while non-native fish tended to respond positively to long- or medium-term dry periods and short-term wet periods. 4. Fish detection probability varied among species, sampling gears, wetland areas and wetlands, indicating that accounting for variable detection can be critical when evaluating patterns in fish abundance. 5. Synthesis and applications. We found that antecedent conditions can be important for determining environmental water allocation policies. Our results indicated that native fish generally responded positively to frequent inundation of wetlands, while non-native species generally responded positively to long dry periods followed by short-term inundation events. For some non-native species, long dry periods not only generated a positive response in abundance, but enhanced the positive response to short-term inundation events. The divergence between native and non-native fishes' responses to antecedent conditions provides opportunities for managers to allocate water to favour native fish assemblages. Future research of environmental flows for managing fish assemblages should consider antecedent conditions and apply models that account for incomplete detection, such as the one developed here, to better inform the management process.

Salmon populations harvested in mixed-stock fisheries can exhibit genotypic, behavioral, and life history diversity that can lead to heterogeneity in population productivity and size. Methods to quantify this heterogeneity among populations in mixed-stock fisheries are not well-established but are critical to assessing harvest–biodiversity trade-offs when setting harvest policies. We developed an integrated, age-structured, state-space model that allows for more complete use of available data and sharing of information than simpler methods. We compared a suite of state-space models of varying structural complexity to simpler regression-based approaches and, as an example case, fitted them to data from 13 Chinook salmon (Oncorhynchus tshawytscha) populations in the Kuskokwim drainage in western Alaska. We found biological and policy conclusions were largely consistent among state-space models but differed strongly from regression-based approaches. Simulation trials illustrated our state-space models were largely unbiased with respect to spawner–recruit parameters, abundance states, and derived biological reference points, whereas the regression-based approaches showed substantial bias. These findings suggest our state-space model shows promise for informing harvest policy evaluations of harvest–biodiversity trade-offs in mixed-stock salmon fisheries.

Accounting for population diversity can be critical to the sustainable management of mixed-stock fisheries because harvest rates that can be sustained by productive populations may come at the cost of overfishing less productive ones. While these harvest–diversity trade-offs are well-recognized, their consequences for harvest policy performance are not often explicitly evaluated in contemporary fisheries management. We use closed-loop simulations to evaluate the ability of alternative harvest policies to meet population diversity and fishery objectives for one of the largest subsistence Chinook salmon (Oncorhynchus tshawytscha) fisheries in the world (Kuskokwim River Basin in western Alaska). We found clear evidence of population diversity that resulted in asymmetric trade-offs among fishery and conservation objectives whereby policies that forgo relatively small amounts of harvest result in relatively large increases in equitable access to Chinook and elimination of risk of weak stock extirpation. The performance of alternative harvest policies, and the magnitude of trade-offs, were sensitive to regime shifts and uncertainty in the drivers of recruitment variation. However, we found that harvest policies that prioritized meeting minimum subsistence needs were unlikely to jeopardize long-term sustainability.

The invasive Burmese python (Python molurus bivittatus) is causing declines in the numbers and diversity of native mammals in the Greater Everglades Ecosystem (GEE). However, limited evidence suggests that some species may be less susceptible to pythons than others. This difference in susceptibility may be a function of different life-history traits. We analysed incidence data with a multi-species hierarchical occupancy model to evaluate the influence of pythons on native mammals and examine the association between python’s influence on species occurrence and life-history traits. We also used our traits-based model to predict the effects of pythons on occupancy probabilities of five mammalian species of conservation or management concern known to occur in the GEE but not detected in our study. Ten of 18 observed mammals showed significant negative effects from pythons, while one responded positively. We found that three of the six species traits evaluated (mass, fecundity, and habitat breadth) moderated the negative effects of pythons on mammal occurrence and were, thus, useful for predicting species responses. Our results suggest larger, fecund and/or species with wide habitat breadths were less susceptible to increasing relative densities of pythons. Our results also suggest a positive and neutral associations between rodents and relative python density, likely due to wide habitat breadths, high fecundity rates, and the reduction of mammalian predators in areas with higher relative python densities. These trait relationships predicted a negative response of all five unobserved species of management concern included in our analysis. Our study provides a broader understanding of wildlife community vulnerability to invasive predators and demonstrates how trait-based models can be used to elucidate generalizable patterns and generate predictions for rare and/or undetected species.

Estimating the size selectivity of fishery users and sampling methods can be difficult to achieve due to data limitations. However, these limitations can be moderated by borrowed information from other sources such as other systems, times, and species. Here we develop a model that integrates an externally sourced boat electrofishing length–vulnerability model with internally sourced boat electrofishing and angling catch data to estimate length-dependent vulnerability of fish to angling in a data-limited situation. We apply the model to Murray cod (Maccullochella peelii) as an example and show that angling for Murray cod selectively captures a narrow range of sizes that includes medium to large size fish. Although boat electrofishing also followed a similar pattern, the range of fish sizes vulnerable to capture was much broader, including a more uniform vulnerability of all size classes evaluated. Understanding the length selectivity to capture has key implications for effective determination of fisheries regulations, as well as interpreting monitoring data. Thus, we see this modelling approach as a good option when more informative data are not available to support the estimation process.

Movement and migration of fish are critical for sustaining riverine fish populations. Water resource development alters natural flow regimes and can disconnect habitats and interfere with hydrological cues for fish movement. Environmental flow releases can counter these impacts, but to be effective they must be based on quantitative flow–biota relationships. We used radio‐telemetry to investigate the association between flow and movement of Tandanus bostocki, a plotosid fish endemic to south‐western Australia. Movement was assessed for 15 adult fish at three temporal scales: weekly, daily and bihourly to reveal seasonal patterns in movement, movement around individual flow pulses, and to describe changes in home range respectively. We used a predictive modelling approach to assess the importance of discharge and other covariates on the directional distance travelled or linear home range size. Our seasonal and flow pulse study revealed that T. bostocki undertook larger downstream movements during higher flows and smaller upstream movements during lower flows. Daily movements tended to be downstream on the ascending limb of flow pulses and upstream on the descending limb. Flow‐dependent movements at weekly or daily time scales were relatively modest (typically hundreds of metres) and were moderated by time of year and gender; however, fish underwent a synchronised 1‐km movement upstream during the known reproductive period in October. The home range study revealed that T. bostocki had larger home ranges (night‐time foraging) when baseflow was elevated. These results can assist the design of customised environmental flows in the study river and other flow‐regulated rivers.

he relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using standardised methods to test the hypothesis that detritivore diversity enhances litter decomposition in streams, to establish the role of other characteristics of detritivore assemblages (abundance, biomass and body size), and to determine how patterns vary across realms, biomes and climates. We observed a positive relationship between diversity and decomposition, strongest in tropical areas, and a key role of abundance and biomass at higher latitudes. Our results suggest that litter decomposition might be altered by detritivore extinctions, particularly in tropical areas, where detritivore diversity is already relatively low and some environmental stressors particularly prevalent., This study was part of the DecoDiv project conducted by the GLoBE network (www.globenetwork.es), which is coordinated by L. B. Most research was based on crowdfunding (details on specific funding sources at each region are given in Supplementary Information). Project coordination was funded by Basque Government funds (Ref. IT951-16) to the Stream Ecology Group (UPV/EHU, Spain).

Rivers around the world are threatened by altered flow due to water resource development. Altered flow can change food webs and impact riverine energetics. The Fitzroy River, in northern Australia, is targeted for development but uncertainty remains about the sources of carbon supporting the food web, particularly in the lowlands—the region most likely to be impacted by water extraction. This study used stable isotopes to investigate if algal biofilm is the main carbon source sustaining fish in lowland habitats. We also sought evidence that large-bodied migratory fish were transporting remote carbon around the system. Our results revealed that local algal biofilm carbon was the dominant source of energy sustaining fish in wet season floodplain habitats, but that fish in main-channel pools during the dry season were increasingly dependent on other carbon sources, such as leaf litter or phytoplankton. We found no evidence that large-bodied fish were transporting remote carbon from the floodplain or estuary into the lower main-channel of the river. We recommend that water planners take a precautionary approach to policy until sufficient food web evidence is amassed.

In grasslands across the world, woody species are replacing grass cover. This bush encroachment can alter available food, cover, and space resources for most mammalian species; however, the specific responses of mammals to bush encroachment in African savannas remain largely unknown. We examined the fine-scale response of mammals across a gradient of bush encroachment using camera traps and a Bayesian hierarchical multi-species abundance model that estimates local relative abundance and species richness while accounting for imperfect detection. Additionally, we simulated species-specific relative abundances and species richness responses to differing bush encroachment management actions. Contrary to our expectations, the relative abundance of only one species showed a negative relationship to shrub cover and another to tree cover. However, the relative abundance of eight out of twenty-one species showed a positive association with grass cover. Mammal species richness increased with grass cover, decreased with shrub cover, and showed no clear pattern with increasing tree cover. Furthermore, our simulations suggest reducing and increasing shrub and grass cover respectively by 50% would increase species richness and local abundances for the mammal community of the area. Our results indicate grass cover exerts a strong influence on habitat use, relative abundances and species richness in bush encroached areas. Our study shows that mammal's positive response to grass cover is more important than potential negative impacts of increasing shrub cover. Consequently, recovering and maintaining adequate grass cover in savannas subject to bush encroachment is an indispensable condition to maximize mammalian diversity and abundances.

Summary 1. Environmental flows are a key restoration technique for conserving ecological function in flow-degraded rivers. Species-specific, flow–biota relationships are increasingly being used to determine environmental flow needs and manage their use; however, many of these relationships are poorly described. 2. We evaluate relationships between environmental variables and spawning intensity for a fish assemblage from the Murray River, Australia, over a ten-year period. We developed a hierarchical multispecies model that accounted for incomplete detection to compare spawning outcomes of native and non-native species using realistic, alternative, water management scenarios. 3. Temperature was an important predictor of spawning intensity for all seven species studied, while both concurrent and antecedent flow conditions were important for many species. Our water management scenario testing accounted for these relationships and indicated that increasing the magnitude of smaller floods following lower antecedent flow conditions, at water temperatures of 18–20C, achieves the greatest spawning outcome for native fish. 4. Synthesis and applications. Our results indicate that principally temperature, and flow as a secondary variable, influence the timing and strength of fish spawning. The synthesis of these spawning relationships predicts that managers will achieve the greatest spawning return per unit of environmental water when flows are applied on top of an existing flow pulse. This study highlights the importance of considering a range of abiotic factors and the use of modelling scenarios to improve environmental flow outcomes.

Summary Relationships between river flow characteristics and fish community/population dynamics (i.e. flow–ecology relationships) underpin methods to determine and monitor environmental water allocations. Quantifying these relationships can be difficult, and consequently, most environmental flow strategies for fish conservation in Australian rivers are based on general flow–ecology relationships as opposed to statistical predictions. Of those studies that have investigated relationships between flow and fish, most have not accounted for incomplete and variable detection of fish by the sampling methods, thus making the implicit assumption that sampling efficiency is invariant. This important assumption is rarely met, leading to inconsistent research findings and spurious results, and a reliance on generic flow–ecology principles for defining flow management strategies. We illustrate how and when detection probability varies when sampling freshwater fish and the consequences to scientific inference about fish–flow relationships. Methods for accounting for imperfect detection of fish are identified and tools to increase the efficiency of experimental designs while reducing sampling cost are discussed. These tools include methods for borrowing information among experimental components and simulation techniques to optimise sampling designs. We argue that, due to the very nature of sampling designs to quantify flow–ecology relationships (e.g. sampling at different flow magnitudes/regimes), the challenge of imperfect detectability is particularly relevant to environmental flow science. We encourage the broader adoption of methods that account for imperfect detection to improve inference about fish–flow relationships and increase the successful application of environmental flows for managing fish communities.

Summary The performance of species richness estimators can be highly variable. Evaluating the accuracy and precision of different estimators for different assemblages is common in the ecological literature, but estimator performance is rarely measured in terms of research goals such as detecting patterns in diversity. We evaluated the efficacy of nonparametric richness estimators to detect changes (i.e. type-I and type-II error rates) in species richness using two experimental designs: a block design and a trend analysis. We also evaluated estimator efficacy across a variety of species-abundance distributions, species number and sample sizes. The evaluation was performed using simulated data that mimicked the qualities of real data to ensure real-world relevance. We found that the bias and precision of all estimators evaluated had high sensitivity to sample size and shifts in the species-abundance distribution. Importantly, all estimators demonstrated elevated type-I error rates when the species-abundance distribution varied. These inflated type-I error rates resulted in spurious conclusions about patterns in species richness. Results suggest that caution should be taken when using nonparametric estimators to detect pattern in species richness. Furthermore, estimator evaluations should always include measures of type-I and type-II error rates. These quantities can reveal the inference consequences of the dependency of estimator bias and precision on community and sampling characteristics.

Reduction in transmitter size used in telemetry studies have allowed researchers to tag and track fish that are much smaller than could have been tagged previously. Researchers seek information on juvenile or small fish movement, behavior, and survival to better understand recruitment processes. Juvenile or small-bodied fish that have been tagged have an increased risk of predation, which results in transmitters being consumed. Knowledge about radio transmitter accumulation in a predator's gut and evacuation times are critical for interpreting locations of radio-tagged fish and their predators. Our objective was to determine what factors influenced the evacuation time of transmitters (0.3 g), implanted in juvenile Largemouth Bass Micropterus salmoides through the digestive system of adult Largemouth Bass that had preyed upon those tagged juveniles. All transmitters ingested by the predators were evacuated within 84 h. A Poisson regression model showed that transit time decreased significantly with...

The degradation of streams caused by urbanization tends to follow predictable patterns; however, there is a growing appreciation for heterogeneity in stream response to urbanization due to the local geoclimatic context. Furthermore, there is building evidence that streams in mildly sloped, permeable landscapes respond uncharacteristically to urban stress calling for a more nuanced approach to restoration. We evaluated the relative influence of local-scale riparian characteristics and catchment-scale imperviousness on the macroinvertebrate assemblages of streams in the flat, permeable urban landscape of Perth, Western Australia. Using a hierarchical multi-taxa model, we predicted the outcomes of stylized stream restoration strategies to increase the riparian integrity at the local scale or decrease the influences of imperviousness at the catchment scale. In the urban streams of Perth, we show that local-scale riparian restoration can influence the structure of macroinvertebrate assemblages to a greater degree than managing the influences of catchment-scale imperviousness. We also observed an interaction between the effect of riparian integrity and imperviousness such that the effect of increased riparian integrity was enhanced at lower levels of catchment imperviousness. This study represents one of few conducted in flat, permeable landscapes and the first aimed at informing urban stream restoration in Perth, adding to the growing appreciation for heterogeneity of the Urban Stream Syndrome and its importance for urban stream restoration.

Altered flow regimes in lakes can change macrophyte habitats from dynamic, species-rich communities to dense, monotypic communities that can change the physicochemical environment available to fish. We tested whether fish community composition, fish density, fish species richness, and fish species diversity changed across a range of dissolved oxygen concentrations (DO; mg/L) in dense stands of several macrophyte species that are commonly the target of macrophyte control efforts in Florida lakes. We sampled fish communities within growths of 5 emergent macrophyte species including cattail (Typha spp.), pickerelweed (Pontedaria cordata), smartweed (Polygonum spp.), torpedograss (Panicum repens), and water primrose (Ludwigia spp.) at lakes Kissimmee and Istokpoga, Florida. Fish communities were sampled using 3 different enclosure gears treated with rotenone, and DO was measured in mid-water column at each site. Macrophyte biomass and DO concentrations were inversely related. Poeciliids accounted for ...

Indices of abundance are commonly used in fisheries stock assessment models to represent trends in population size over time; however, an index can misrepresent such trends when catchability varies, sampling gears change or spatial sampling frames shift. Here we develop a state-space model in a Bayesian framework that combines both chevron trap catches and video counts into a single integrated index. The modeling approach accounts for variation in sampling efficiency (catchability) of both sampling gears and adjusts for aspects of changes in the spatial sampling frame (sampling intensity and spatial coverage) through time due to monitoring program development. We validate the model using a simulation study and then demonstrate its utility using data on vermilion snapper Rhomboplites aurorubens from the period 1990–2016. The index suggests high variation in the abundance of vermilion snapper, particularly for years previous to 2000 and a systematic decline in abundance between the early 1990s and 2016. This pattern culminates (2016) with vermilion snapper at about 16% of their average early 1990s abundance which is a stronger decline than is indicated by the current index used for stock assessment of the species.

Managing fisheries using length-based harvest regulations is common, but such policies often create trade-offs among conservation (e.g. maintaining natural agestructure or spawning stock biomass) and fishery objectives (e.g. maximizing yield or harvest numbers). By focusing harvest on the larger (older) fish, minimumlength limits are thought to maximize biomass yield, but at the potential cost of severe age and size truncation at high fishing mortality. Harvest-slot-length limits (harvest slots) restrict harvest to intermediate lengths (ages), which may contribute to maintaining high harvest numbers and a more natural age-structure. However, an evaluation of minimum-length limits vs. harvest slots for jointly meeting fisheries and conservation objectives across a range of fish life-history strategies is currently lacking. We present a general age- and size-structured population model calibrated to several recreationally important fish species. Harvest slots and minimum-length limits were both effective at compromising between yield, numbers harvested and catch of trophy fish while conserving reproductive biomass. However, harvest slots consistently produced greater numbers of fish harvested and greater catches of trophy fish while conserving reproductive biomass and a more natural population age-structure. Additionally, harvest slots resulted in less waste in the presence of hooking mortality. Our results held across a range of exploitation rates, life-history strategies and fisheries objectives. Overall, we found harvest slots to represent a valuable option to meet both conservation and recreational fisheries objectives. Given the ubiquitous benefits of harvest slots across all life histories modelled, rethinking the widespread use of minimum-length limits is warranted.

Fisheries assessments often rely on age composition data to infer information about growth, mortality, and the outcome of various management policies. To reduce the costs of estimating the age of all fish collected (i.e., via direct aging), an age–length key (ALK) is often developed by directly aging only a subsample of fish and estimating the ages of the remaining fish based on observed lengths. Although this approach is common, there is little guidance in the literature for determining the appropriate total sample size and numbers of fish needed to directly age for each length bin. We developed a stochastic simulation to evaluate the sample-size requirement for using ALKs to estimate von Bertalanffy growth parameters and the instantaneous rate of total mortality (Z). The simulations accounted for variation in life history characteristics of stocks and exploitation rates of fisheries. Our simulations suggested that for overfished populations, aging more fish per bin provides negligible benefits ...

Electrofishing CPUE data are commonly used to index temporal trends in abundance in fish monitoring programs, but the reliability of this index requires the assumption that the fraction of fish stock caught per unit effort (catchability, q) is relatively precise and constant through time. We evaluated how fish species, season, and lake affected electrofishing catchability in Florida lakes using a field study. We used the field study results to simulate how variable electrofishing q affects statistical power and type I error rate (i.e., the probability of detecting a difference when in fact no difference occurred). Model selection showed that electrofishing catchability varied by species, season, and lake, and submodels showed that catchability varied by lake for Largemouth Bass Micropterus salmoides and by season for Lake Chubsucker Erimyzon sucetta, and was constant across season and lake for Bluegill Lepomis macrochirus. Our results revealed that statistical power decreased and the type I error...

Predation risk can impact population dynamics and ecosystem structure. Changes in key habitats, such as shifts between types of submersed aquatic vegetation, may affect predation risks experienced by certain organisms that use vegetation as a predation refuge. Relative predation risks experienced by Lucania parva (Baird & Girard) were assessed among three habitats in a Florida coastal stream using tethering experiments. Relative predation risks were highest in bare substrate, intermediate in a rooted macrophyte, Vallisneria americana Michx, and lowest in filamentous macroalgae. These results suggest that L. parva predation risk may decline following shifts from macrophytes to filamentous macroalgae, potentially leading to increased L. parva population size. These findings counter a widely held perception that such habitat shifts yield exclusively negative faunal effects, and are useful for assessing implications of habitat change and guiding restoration activities.

Macquarie perch, Macquaria australasica Cuvier, is an endangered Australian freshwater fish that has historically supported popular recreational fisheries, but since the 1980s, it has experienced a decline in both distribution and abundance. This study investigated whether a marked decline in the population size of Macquarie perch has occurred at Lake Dartmouth between the mid-1980s and 2000 and the likelihood of the current legal minimum length (LML) of 350 mm TL protecting the population from recruitment overfishing. Recreational angler survey data showed strong evidence for a temporal population decline. Sampling of the population and construction of a simulation model indicated that the current LML would protect the population from recruitment overfishing. This study highlights the value of specifically investigating suspected threats to endangered fish populations to allow the instigation of effective fisheries management.

Throw traps are commonly used to assess small fish and macroinvertebrate (SFI) communities in aquatic habitats. Traditionally, numerous passes with a bar seine are used to remove all SFIs from within the throw trap, providing density estimates that are comparable across habitat types. However, similar information can be gathered with fewer seine passes than are traditionally used, thus allowing more sampling in a given field effort. The appropriate number of seine passes to meet study objectives can be determined if habitat-specific recovery probabilities are estimated. We investigated how SFI recovery probabilities within throw traps varied among five submerged aquatic vegetation habitat types and how these recovery probabilities can be used to determine the number of seine passes necessary to assess and detect differences in SFI relative abundance. Using a 1-m2 throw trap and bar seine, we found that estimates of SFI recovery probability were high (75–80%) and similar across habitats. Because o...

Size-selective fish sampling can strongly bias von Bertalanffy growth parameter estimates. Bias-correction methods have been developed, but they often require previous knowledge of selectivitypattern, capture–recapture data or intensive age-growth sampling over multiple consecutive years.When corrective measures are not feasible, investigators have attempted a number of biologically basedprocedures to reduce this bias. We evaluated several existing biologically based procedures that couldpotentially remove bias from growth parameter estimates. We built an age and length structured popu-lation model and tested the utility of four procedures to remove bias: 1) fixing t 0 at zero, 2) deleting dataassociated with ages that are not fully vulnerable to sampling, 3) deleting less than fully vulnerable agesand fixing t 0 at zero, and 4) fixing L ∞ at the maximum value observed in the data. We considered sam-pling gears that had no size selectivity, asymptotic selectivity, and dome-shaped selectivity patterns forall procedures. Results suggested that none of these procedures would eliminate bias in growth param-eters across all three gear selectivity patterns. Investigators should attempt to use methods to correctgrowth parameters for size selectivity of sampling gears (e.g., mark recapture methods). If such correc-tions are not feasible, prior information about the size selectivity pattern of sampling gears is necessaryfor informed selection of biologically based von Bertalanffy fitting procedures.© 2010 Elsevier B.V. All rights reserved.

Many aquatic systems worldwide have experienced significant changes in littoral macrophyte communities from altered hydrology in the form of water controls structures (e.g., dams). Water level stabilization for flood control can cause persistent occurrence of dense stands of emergent macrophytes, which can affect the physicochemical environment for fishes. We evaluated dissolved oxygen (DO) concentrations in five emergent macrophyte species (cattail Typha spp., pickerelweed Pontedaria cordata, smartweed Polygonum spp., torpedograss Panicum repens, and water primrose Ludwigia spp.) at three levels of macrophyte coverage (i.e., 50–64, 65–79, and 80–95%) at Lake Istokpoga, Florida during July–August (summer) and October–November (fall) 2007. Dissolved oxygen exhibited substantial spatial and temporal variability at small scales (i.e., meters and hours), with the lowest DO and highest probability of hypoxia occurring in smartweed and water primrose habitats relative to other macrophyte types. The probability of hypoxia increased with macrophyte coverage for all macrophyte species tested. Dissolved oxygen was influenced by the structural differences (e.g., stem density and size) and spatial orientation (e.g., proximity to open water) associated with the individual macrophyte habitats. Restoration efforts that create open water pathways and maximize edge areas might improve DO concentrations and habitat quality and quantity for freshwater fishes.

We used an age-structured model to evaluate the impacts of recreational angling during spawning on populations of largemouth bass Micropterus salmoides and the potential benefits of seasonal fishing closures. We simulated fisheries with average and high capture rates (i.e., fractions of the stock caught by anglers). We manipulated mortality rates to mimic the effects of various regulations, including (1) an open fishery with no closures, (2) a full fishery closure during the spawning season, (3) a catch-and-release fishery during the spawning season, and (4) a year-round catch-and-release fishery. We simulated two hypothetical populations: a high-productivity, low-latitude population and a low-productivity, high-latitude population. Spawning season closures produced the largest relative increases in adult abundance when applied to low-productivity populations and when capture rates were high (e.g., 70%) and harvest rates were relatively low (20%). This resulted because very high capture rates imp...

Assessing the Potential for the Angling of Nesting Males to Influence Largemouth Bass Recruitment Should Consider the Quality of Nesting Individuals: Response to Comment Michael S. Allen a , Mark W. Rogers a , Matthew J. Catalano a , Daniel C. Gwinn a & Stephen J. Walsh b a School of Forest Resources and Conservation, University of Florida, 7922 North West 71st Street, Gainesville, Florida, 32653, USA b U.S. Geological Survey, Southeast Ecological Science Center, 7920 North West 71st Street, Gainesville, Florida, 32653, USA Published online: 01 Feb 2013.

Field surveys and field experiments have previously documented adverse effects of solid byproducts from coal incineration (coal combustion wastes (CCW)) on larval amphibians inhabiting aquatic habitats. However, a definitive link between CCW-exposure and developmental abnormalities has not been established because no studies have addressed the direct effects of prolonged exposure to CCW on larval amphibian development under controlled laboratory conditions. In the laboratory we exposed green frog (Rana clamitans) and wood frog (Rana sylvatica) larvae to either clean sand or CCW-contaminated sediment to investigate the direct effects of CCW exposure on trace element accumulation, growth, developmental rate, malformations, survival, and metamorphic success. While both species accumulated significant (P0.05) concentrations of at least six trace elements (As, Cd, Fe, Se, Sr, and V), effects of exposure to CCW varied between species, with R. clamitans larvae experiencing more severe effects including a 26% reduction in survival and a 45% reduction in metamorphic success. Furthermore, exposure to CCW decreased growth and developmental rates among larvae of both species that successfully completed metamorphosis. Larval period duration was increased by 10 and 11%, and size at metamorphosis was decreased by 10 and 39% in R. clamitans and R. sylvatica exposed to CCW, respectively. Rates of malformations were/= 4%, and were not dependent on species or sediment treatment. Our results confirm the direct effects of CCW on aquatic amphibian larvae suggested by previous field studies, and indicate that considerable variation may exist in sensitivity among species exposed to CCW. These findings have important implications for the management of CCW since50 million t are discharged annually to surface impoundments in the US, which are often used by breeding amphibians.

Invasive fish species can present difficult management problems, particularly when the species has recreational value. One such case is redfin perch in Lake Purrumbete, Australia, which have recreational value but have become invasive in the lake. In this study we evaluated removal strategies for redfin perch in Lake Purrumbete with the aim of improving the quality of the recreational fishery. We evaluated removal scenarios for redfin perch with a population model and conducted a sensitivity analysis to determine the robustness of our general results. The results suggest that removal scenarios that direct exploitation, on an annual time scale, at fish ≤150-mm total length, with high levels of exploitation, will result in the greatest reduction in small undesirable fish and the greatest increase in large desirable fish in the lake. This was consistent across most assumptions about life-history characteristics, density-dependent processes and population dynamics rates, suggesting that this management strategy is robust to most relevant biological uncertainties. Furthermore, exploiting redfin perch on an annual time scale would result in the lowest annual variation in the population because of disruption of the age and size structure. These results can help managers choose strategies to manipulate the fishery of Lake Purrumbete to achieve more desirable characteristics.

Sampling designs for effective monitoring programs are often specific to individual systems and management needs. Failure to carefully evaluate sampling designs of monitoring programs can lead to data that are ineffective for informing management objectives. We demonstrated the use of an individual-based model to evaluate closed-population mark–recapture sampling designs for monitoring fish abundance in open systems, using Murray cod (Maccullochella peelii (Mitchell, 1838)) in the Murray–Darling River basin, Australia, as an example. The model used home-range, capture-probability and abundance estimates to evaluate the influence of the size of the sampling area and the number of sampling events on bias and precision of mark–recapture abundance estimates. Simulation results indicated a trade-off between the number of sampling events and the size of the sampling reach such that investigators could employ large sampling areas with relatively few sampling events, or smaller sampling areas with more sampling events to produce acceptably accurate and precise abundance estimates. The current paper presents a framework for evaluating parameter bias resulting from migration when applying closed-population mark–recapture models to open populations and demonstrates the use of simulation approaches for informing efficient and effective monitoring-program design.

In a longitudinal study of two streams whose lower reaches received unattenuated urban stormwater runoff, physical disturbance by stormflow was less important than the persistant unidentified chemical impacts of urban stormwater in limiting the distribution of Chironomidae, and Ephemeroptera, Trichoptera and Plecoptera (EPT). A hierarchical spatial analysis showed that chironomid density did not decrease from rural to urban stream reaches. Instead, the taxonomic composition of chironomid assemblages was significantly altered in urban versus rural reaches; chironomid assemblages in urban reaches exhibited higher average pollution tolerance scores. In contrast, the density of EPT was significantly lower in urban reaches. Despite higher values of stormflow tractive force in urban reaches, streambed stability tended to be greater in urban reaches. Modeling of temporal variation in chironomid density showed similar patterns in both rural and urban reaches: chironomid density had a unimodal relationship to rainfall index (RI), with highest densities at intermediate values of RI. Models of EPT density over time in rural reaches showed no significant relation to RI, and temporal variation in EPT density in urban reaches was not predictable. The abundance of fine particulate organic matter, including periphyton (FPOM), on cobbles was greater in urban reaches and showed a much greater degree of temporal variation than in rural reaches. In urban reaches, a negative relation between FPOM and RI indicated the importance of stormflow abrasion.