Culvert Replacement and Stream Habitat Restoration: Implications from Brook Trout Management in an Appalachian Watershed, U.S.A

Mitigation bank applications for freshwater systems: Control mechanisms, project complexity, and caveats

Biodiversity and mitigation banking has become a popular alternative offsetting mechanism, especially for freshwater species and systems. Central to this increase in popularity is the need for sound control mechanisms to ensure offset functionality. Two commonly used mechanisms are monitoring requirements and staggered release of bank credits over time. We used data from 47 banks in the United States, targeting freshwater systems and species. Based on the 47 banks meeting our criteria we showed that control mechanisms generally scale with increased project complexity and that banks release most of their total credit amount within the first 3 years. We further showed that advance credits are common and can increase the potential for credit release without providing tangible ecological benefits. Physical and biological assessment criteria commonly used by banks let us identify three main bank types focusing on connectivity, physical aspects, and habitat and species and their application possibilities and caveats to provide different ecosystem benefits for freshwater species and systems affected by anthropogenic development.

What Makes A Bank A Bank? Differences and Commonalities in Credit Calculation, Application, and Risks in Mitigation Banks Targeting Freshwater Fish Species and Associated Ecosystems

Mitigation banking is part of the ever-expanding global environmental market framework that aims to balance negative approved anthropogenic impacts versus third-party provided ecosystem benefits, sold in the form of credits. Given the need to conserve freshwater biodiversity and habitat, banking has received great traction for freshwater species and systems. While extensive reviews and studies have been conducted on evaluating if equivalency between impacts and offset can be achieved, there is almost no research being done on the way credits are being generated and banks are managed to inform future best practice and policy. Synthesizing banking data through cluster analyzes from 26 banks in the United States generating credits for freshwater species and associated systems, we show two generalizable approaches: removing barriers and targeting whole communities. Both address crucial freshwater conservation needs but come with their risks and caveats. Using common characteristics and management practices founded in federal and district level guidance within these two groups, we showcase and conclude that credit generation via barrier removal can be at risk of granting credit generation for too large of an area, leading to over-crediting. Banks targeting whole freshwater communities and accounting for landscape-level interactions and influences can potentially be detrimental for species on an individual level and large-scale credit availability as well as transfer can incentivize non-compliance with the mitigation hierarchy.

Urban buried streams: Abrupt transitions in habitat and biodiversity

Stream burial, the rerouting of streams into underground culverts, is common in industrialized and densely populated urban areas. While stream burial is common in urban environments, direct characterization of the within-culvert environment is rare and it is unclear if buried reaches reflect neighboring open reaches regarding habitat, biota, and water chemistry. Additionally, for a buried stream, the entrance and exit of the culvert are abrupt habitat transitions within the stream channel, and it is unknown if these transitions lead to similarly abrupt responses in biotic and abiotic characteristics or if responses are gradual. Quantifying the within-culvert environment and transitions upon entering/exiting the culvert has rarely been done but can help inform management practices regarding how these systems are impacted and establish a baseline for evaluating daylighting or stream restoration projects. To understand how culverts affect longitudinal biotic and abiotic characteristics of urban streams, we evaluated longitudinal patterns of physical habitat characteristics, stream water physiochemistry, periphyton biomass, and macroinvertebrate density and diversity in two urban streams that included long (>100 m) culvert reaches. Abrupt transitions in a suite of abiotic and biotic variables were observed at the entrances and exits of the culverts whereas some variables showed no response to the culvert presence. Periphyton biomass and macroinvertebrate density were reduced by 98% and 92%, respectively, by culverts in the two streams. Within the culverts, we observed greater water depths (average of 10 cm outside vs 26 cm within the culvert), finer benthic substrate, and diversity of macroinvertebrates was reduced by 50%. Nutrient concentrations, in contrast, showed no response to the presence of a culvert. Within 60-90 m downstream of the culvert exits, most of the measured parameters returned to levels similar to those observed upstream of the culvert, suggesting that the ecosystem impacts of urban culverts, though dramatic, may be spatially constrained.

Missing Compensation: A Study of Compensatory Mitigation and Fish Passage in Georgia

Thousands of permit applications are filed annually with the U.S. Army Corp of Engineers, requiring significant review efforts to ensure that applications conform to regulations, and that proposed activities avoid, minimize, and compensate for stream and wetland impacts. However, the effectiveness of this approach remains uncertain. We evaluated the effectiveness of those regulatory efforts using newly installed stream–road crossings as a case study because crossings are pervasive on the landscape and many U.S. Army Corp of Engineers jurisdictions have requirements that are aimed at minimizing crossing-induced impacts to fish passage. Specifically, we assessed whether requirements intended to facilitate fish passage were implemented, whether requirements resulted in fish-passable stream–road crossings, and whether the amount of construction-related stream impact that was authorized by permits corresponded to the amount of compensation that was required. Our analysis is devoted solely to stream–road crossings in Georgia that are permitted under nationwide permits, the permit type commonly used to authorize activities in streams throughout the United States. We found that no new crossings conformed entirely to the requirements intended to avoid and minimize impacts to fish passage. The measured total stream impact length in this study was 46.0% higher than the amount of impact proposed in permit applications for perennial streams, and 23.7% higher for intermittent and ephemeral streams. Only 30.6% of the perennial stream length affected in this study received compensation for impacts even though 90.9% of impacts qualified. Collectively, these results indicate that regulations and mitigation policies are not having their intended effects of providing fish passage or preventing net loss of streams in Georgia as required under the Clean Water Act. We recommend that decision makers undertake a more geographically comprehensive evaluation of stream impacts that are authorized by permits to thoroughly evaluate regulatory effectiveness and impacts to fish passage.

Telemetry-Determined Habitat Use Informs Multi-Species Habitat Management in an Urban Harbour

Widespread human development has led to impairment of freshwater coastal wetlands and embayments, which provide critical and unique habitat for many freshwater fish species. This is particularly evident in the Laurentian Great Lakes, where such habitats have been severely altered over the last century as a result of industrial activities, urbanization, dredging and infilling. In Toronto Harbour, extensive restoration efforts have been directed towards improving the amount and quality of aquatic habitat, especially for fishes. To evaluate the effectiveness of this restoration work, use of the restored area by both target species and the fish community as a whole must be assessed. Individuals from four species (Common Carp, Largemouth Bass, Northern Pike and Yellow Perch) were tagged and tracked continuously for 1 year using an acoustic telemetry array in Toronto Harbour area of Lake Ontario. Daily site fidelity was estimated using a mixed-effects logistic regression model. Daily site fidelity was influenced by habitat restoration and its interactions with species and body size, as well as season and its interactions with species and body size. Daily site fidelity was higher in restored sites compared to non-restored sites for Yellow Perch and Northern Pike, but lower for Largemouth Bass and Common Carp. For all species, daily site fidelity estimates were highest during the summer and lowest during autumn. The approach used here has merit for evaluating restoration success and informing future habitat management activities. Creating diverse habitats that serve multiple functions and species are more desirable than single-function-oriented or single-species-oriented designs.

More than a corridor: use of a main stem stream as supplemental foraging habitat by a brook trout metapopulation

Coldwater fishes in streams, such as brook trout (Salvelinus fontinalis), typically are headwater specialists that occasionally expand distributions downstream to larger water bodies. It is unclear, however, whether larger streams function simply as dispersal corridors connecting headwater subpopulations, or as critical foraging habitat needed to sustain large mobile brook trout. Stable isotopes (δ(13)C and δ(15)N) and a hierarchical Bayesian mixing model analysis was used to identify brook trout that foraged in main stem versus headwater streams of the Shavers Fork watershed, West Virginia. Headwater subpopulations were composed of headwater and to a lesser extent main stem foraging individuals. However, there was a strong relationship between brook trout size and main stem prey contributions. The average brook trout foraging on headwater prey were limited to 126 mm standard length. This size was identified by mixing models as a point where productivity support switched from headwater to main stem dependency. These results, similar to other studies conducted in this watershed, support the hypothesis that productive main stem habitat maintain large brook trout and potentially facilitates dispersal among headwater subpopulations. Consequently, loss of supplementary main stem foraging habitats may explain loss of large, mobile fish and subsequent isolation of headwater subpopulations in other central Appalachian watersheds.

Connectivity and conditional models of access and abundance of species in stream networks

Barriers to passage of aquatic organisms at stream road crossings are a major cause of habitat fragmentation in stream networks. Accordingly, large investments have been made to restore passage at these crossings, but often without estimation of population-level benefits. Here, we describe a broad-scale approach to quantifying the effectiveness of passage restoration in terms interpretable at population levels, namely numbers of fish and length of stream gained through restoration, by sampling abundance in a study design that accounts for variable biogeographic species pools, variable stream and barrier configurations, and variable probabilities of capture and detectability for multiple species. We modified an existing zero-inflated negative-binomial model to estimate the probability of site access, abundance conditional on access, and capture probability of individual fish. Therein, we modeled probability of access as a function of gradient, stream road-crossing type, and downstream access by fish simultaneously with a predictive model for abundance at sites accessible to fish. Results indicated that replacement of barriers with new crossing designs intended to allow for greater movement was associated with dramatically higher probability of access for all fishes, including migratory Pacific salmon, trout, sculpin, and lamprey. Conversely, existing non-replaced crossings negatively impacted fish distributions. Assuming no downstream constraints on access, we estimated the potential length of stream restored by the program ranged between 7.33 (lamprey) and 15.28 km (small coastal cutthroat and rainbow trout). These contributions represented a fraction of the total length available upstream (187 km) of replaced crossings. When limited ranges of species were considered, the estimated contributions of culvert replacement were reduced (1.65-km range, for longnose dace to 12.31 km for small coastal cutthroat and rainbow trout). Numbers of fish contributed ranged from less than 500 (longnose dace) to greater than 100 000 (sculpin). Although our framework can address the question of effectiveness in a broad array of stream and crossing configurations, much stronger inferences would be possible if future restoration efforts were designed to address the limitations we encountered in this study, particularly the lack of available information on crossings and species presence prior to restoration, and nonrandom selection of crossings to be replaced.

Macrobenthos habitat potential mapping using GIS-based artificial neural network models

This paper proposes and tests a method of producing macrobenthos habitat potential maps in Hwangdo tidal flat, Korea based on an artificial neural network. Samples of macrobenthos were collected during field work, and eight control factors were compiled as a spatial database from remotely sensed data and GIS analysis. The macrobenthos habitat potential maps were produced using an artificial neural network model. Macrobenthos habitat potential maps were made for Macrophthalmus dilatatus, Cerithideopsilla cingulata, and Armandia lanceolata. The maps were validated by compared with the surveyed habitat locations. A strong correlation between the potential maps and species locations was revealed. The validation result showed average accuracies of 74.9%, 78.32%, and 73.27% for M. dilatatus, C. cingulata, and A. lanceolata, respectively. A GIS-based artificial neural network model combined with remote sensing techniques is an effective tool for mapping the areas of macrobenthos habitat potential in tidal flats.

Culverts in paved roads as suitable passages for Neotropical fish species

Improperly installed or poorly maintained culverts can pose a serious threat to fish by disrupting their habitat and endangering spawning success. Road culverts that are not designed for fish passage frequently can become obstacles. This can be especially problematic for migratory species, but can lead to fragmentation of resident populations as well. This study evaluated 40 culverts of 29 sites within a 25-km radius from Toledo city, Paraná State, southern Brazil, with respect to their likely effects on movement of the local ichthyofauna. We collected data on the shape and length of culverts, culvert material, waterfall height, water column depth, slope, and estimated flow velocity. Culverts were categorized by level of barrier risk for upstream migration: high, medium, low, and impassable, as well as the type of barrier posed (fall height, depth, length and velocity). Most of culverts analyzed were considered potential barriers to fish movement, with 45% classified as impassible, 45% as high risk, 10% as medium risk, and no culverts as low risk. Brazilian culverts as fishways will require additional monitoring and studies to corroborate the premises proposed in the present study. Road culvert projects that are properly built and maintained will be able to simultaneously improve function of roadways and protect fish populations.

Fish dispersal in fragmented landscapes: a modeling framework for quantifying the permeability of structural barriers

Dispersal is a key determinant of the spatial distribution and abundance of populations, but human-made fragmentation can create barriers that hinder dispersal and reduce population viability. This study presents a modeling framework based on dispersal kernels (modified Laplace distributions) that describe stream fish dispersal in the presence of obstacles to passage. We used mark-recapture trials to quantify summer dispersal of brook trout (Salvelinus fontinalis) in four streams crossed by a highway. The analysis identified population heterogeneity in dispersal behavior, as revealed by the presence of a dominant sedentary component (48-72% of all individuals) characterized by short mean dispersal distance (<10 m), and a secondary mobile component characterized by longer mean dispersal distance (56-1086 m). We did not detect evidence of barrier effects on dispersal through highway crossings. Simulation of various plausible scenarios indicated that detectability of barrier effects was strongly dependent on features of sampling design, such as spatial configuration of the sampling area, barrier extent, and sample size. The proposed modeling framework extends conventional dispersal kernels by incorporating structural barriers. A major strength of the approach is that ecological process (dispersal model) and sampling design (observation model) are incorporated simultaneously into the analysis. This feature can facilitate the use of prior knowledge to improve sampling efficiency of mark-recapture trials in movement studies. Model-based estimation of barrier permeability and its associated uncertainty provides a rigorous approach for quantifying the effect of barriers on stream fish dispersal and assessing population dynamics of stream fish in fragmented landscapes.