A Meta-analysis on the Effectiveness of Offsetting Strategies to Address Harm to Freshwater Fishes.

Offsetting aims to compensate for negative impacts due to authorized anthropogenic impacts associated with development. While anchored into legislation, residual or chronic impacts can occur after offset establishment. Advice and best practice on how to approach these impacts is rare. To address this, we reviewed 30 projects based on a systematic review and meta-analysis in freshwater ecosystems dealing with residual or long-term negative impacts to provide application advice for: habitat creation, habitat restoration, and biological and chemical manipulation. Project information was obtained through Boolean search terms and web-scraping. Habitat creation projects had a pooled effect size of 0.8 and offsetting ratios of 1:5 with high biomass increases of >140% compared to pre-establishment, associated with them. Habitat restoration projects targeted a wide range of species and communities with a pooled effect size of 0.66, offset ratios ranging from 1:1.2 to 1:4.6, and biomass increases generally > 100% compared to pre-restoration. Biological manipulation had the lowest effect size (0.51) with stocking being highly variable both in terms of biomass benefits and project outcomes pointing towards being mostly applicable in cases of direct fish harm not related to habitat aspects. We conclude that (1) all three assessed approaches have a potential application use for offsetting residual or chronic harm with approach-specific caveats. (2) Implementation costs differ across offset methods, with connectivity and side-channel projects having the lowest biomass gain per area costs (3) Time to first benefits required one to two years with time lags needing to be accounted for in the implementation and monitoring process.

Compliance with and ecosystem function of biodiversity offsets in North American and European freshwaters.

Land-use change via human development is a major driver of biodiversity loss. To reduce these impacts, billions of dollars are spent on biodiversity offsets. However, studies evaluating offset project effectiveness that examine components such as the overall compliance and function of projects remain rare. We reviewed 577 offsetting projects in freshwater ecosystems that included the metrics project size, type of aquatic system (e.g., wetland and creek), offsetting measure (e.g., enhancement, restoration, and creation), and an assessment of the projects' compliance and functional success. Project information was obtained from scientific and government databases and gray literature. Despite considerable investment in offsetting projects, crucial problems persisted. Although compliance and function were related to each other, a high level of compliance did not guarantee a high degree of function. However, large projects relative to area had better function than small projects. Function improved when projects targeted productivity or specific ecosystem features and when multiple complementary management targets were in place. Restorative measures were more likely to achieve targets than creating entirely new ecosystems. Altogether the relationships we found highlight specific ecological processes that may help improve offsetting outcomes.

Cumplimiento y Función Ambiental de las Compensaciones por Biodiversidad en las Aguas Dulces de América del Norte y Europa Resumen El cambio del uso de suelo causado por el desarrollo humano es un causante fundamental de la pérdida de biodiversidad. Para reducir estos impactos se gastan miles de millones de dólares en las compensaciones por biodiversidad. Sin embargo, todavía son raros los estudios de evaluación de la efectividad de los proyectos de compensación que examinen componentes como el cumplimiento general y la función de los proyectos. Revisamos 577 proyectos de compensación en ecosistemas de agua dulce que incluyeran las medidas del tamaño del proyecto, el tipo de ecosistema acuático (p. ej.: arroyo, humedal), la medida de compensación (p. ej.: mejoramiento, restauración, creación) y una evaluación del cumplimiento y el éxito funcional del proyecto. La información sobre los proyectos se obtuvo de bases de datos científicas y del gobierno y de la literatura gris. A pesar de la inversión considerable que existe para los proyectos de compensación persistieron problemas cruciales. Aunque el cumplimiento y la función estuvieron relacionados entre sí, un nivel alto de cumplimiento no garantizó un nivel alto de función. Sin embargo, los proyectos grandes en relación con el área tuvieron una mejor función que los proyectos pequeños. La función incrementó cuando los proyectos se enfocaban en la productividad o en características específicas del ecosistema y cuando los objetivos complementarios de manejo estaban en orden. Las medidas de restauración tuvieron mayor probabilidad de lograr los objetivos que la creación de un ecosistema totalmente nuevo. En general, las relaciones que encontramos resaltan los procesos ecológicos que podrían ayudar a mejorar los resultados de la compensación.

Biological Factors Moderate Trace Element Accumulation in Fish along an Environmental Concentration Gradient.

Trace elements can accumulate in aquatic food webs, becoming potentially hazardous to wildlife and human health. Whereas many studies have examined mercury dynamics in freshwater environments, evidence for the bioaccumulative potential of other trace elements (e.g., arsenic) is conflicting. Trace element concentrations found in surface water of the Red Deer River, Alberta, Canada, have raised concern for potential accumulation in aquatic biota. We investigated fish from this river to better understand the influence of biological and environmental factors in trace element bioaccumulation. We analyzed 20 trace elements, and stable nitrogen (δ15 N) and carbon (δ13 C) isotopes, in the muscle tissue of 8 species. Zinc, selenium, arsenic, chromium, and nickel were detected in the majority of fish at low concentrations. However, mercury was detected in all fish and often exceeded criteria for the protection of consumers. Body size was often positively correlated with trace element concentrations. In addition, δ15 N and δ13 C were correlated to mercury and arsenic concentrations, indicating that mercury biomagnifies whereas arsenic biodiminishes. Spatial patterns of fish trace element concentrations did not reflect differences in surface water concentrations. These findings indicate that fish trace element concentrations are primarily moderated by biological factors, such as trophic position and body size, and are not locally restricted to areas of relatively high environmental concentrations in the Red Deer River. Environ Toxicol Chem 2021;40:422-434. © 2020 SETAC.

Mercury bioaccumulation in stream fish from an agriculturally-dominated watershed.

Bioaccumulation of mercury in freshwater fish is a complex process driven by environmental and biological factors. In this study, we assessed mercury in fish from four tributaries to the Red Deer River, Alberta, Canada, which are characterized by high surface water mercury concentrations. We used carbon (δ13C) and nitrogen (δ15N) stable isotopes to examine relationships between fish total mercury (THg) concentrations, food web dynamics and patterns in unfiltered THg and methylmercury (MeHg) concentrations. We found that THg concentrations exceeded the tissue residue quality guideline for the protection of wildlife consumers in 99.7% of fish sampled. However, while the surface water THg concentration was highest in Michichi Creek and the MeHg concentration was consistent across streams, patterns of fish THg concentrations varied depending on species. Furthermore, body size and trophic level were only correlated with THg concentrations in white sucker (Catostomus commersoni) and Prussian carp (Carrasius gibelio). The results of this study suggest that mercury poses a risk to the health of piscivorous wildlife in the Red Deer River watershed. Despite high THg concentrations in these streams, mercury bioaccumulation is not driven by environmental inorganic mercury concentrations. Additionally, commonly cited factors associated with mercury concentrations in fish, such as body size and trophic level, may not strongly influence bioaccumulation in these stream ecosystems.

Native freshwater species get out of the way: Prussian carp (Carassius gibelio) impacts both fish and benthic invertebrate communities in North America.

Prussian carp (Carassius gibelio) are one of the most noxious non-native species in Eurasia. Recently, Prussian carp, a non-native freshwater fish species, were genetically confirmed in Alberta, Canada and have been rapidly expanding their range in North America since establishment. Given their rapid range expansion, there is an increasing need to determine how Prussian carp may impact native species. We assessed the severity of the Prussian carp invasion by (i) determining their impact on fish communities, (ii) assessing their impact on benthic invertebrate communities, (iii) evaluating if Prussian carp alter abiotic conditions, and (iv) identifying where we find higher abundances of Prussian carp. When Prussian carp were established, we found significant changes to the fish community. Correspondingly, the degree of impact to benthic invertebrate communities was related to the stage of invasion (none, early or recent), where changes in fish communities were significantly concordant with changes in benthic invertebrate communities. Finally, we found that higher abundances of Prussian carp were significantly associated with lower abundances of a majority of native fish species. Altogether, using three lines of evidence, we determine that Prussian carp can have wide-ranging impacts on freshwater ecosystems in North America, pressing the need for management intervention.

Climate change risks, extinction debt, and conservation implications for a threatened freshwater fish: Carmine shiner (Notropis percobromus).

Climate change is affecting many freshwater species, particularly fishes. Predictions of future climate change suggest large and deleterious effects on species with narrow dispersal abilities due to limited hydrological connectivity. In turn, this creates the potential for population isolation in thermally unsuitable habitats, leading to physiological stress, species declines or possible extirpation. The current extent of many freshwater fish species' spatio-temporal distribution patterns and their sensitivity to thermal impacts from climate change - critical information for conservation planning - are often unknown. Carmine shiner (Notropis percobromus) is an ecologically important species listed as threatened or imperilled nationally (Canada) and regionally (South Dakota, United States) due to its restricted range and sensitivity to water quality and temperature. This research aimed to determine the current distribution and spatio-temporal variability in projected suitable habitat for Carmine shiner using niche-based modeling approaches (MaxEnt, BIOCLIM, and DOMAIN models). Statistically downscaled, bias-corrected Global Circulation Models (GCMs) data was used to model the distribution of Carmine shiner in central North America for the period of 2041-2060 (2050s). Maximum mean July temperature and temperature variability were the main factors in determining Carmine shiner distribution. Patterns of projected habitat change by the 2050s suggest the spatial extent of the current distribution of Carmine shiner would shift north, with >50% of the current distribution changing with future projections based on two Representative Concentrations Pathways for CO2 emissions. Whereas the southern extent of the distribution would become unsuitable for Carmine shiner, suitable habitats are predicted to become available further north, if accessible. Importantly, the majority of habitat gains for Carmine shiner would be in areas currently inaccessible due to dispersal limitations, suggesting current populations may face an extinction debt within the next half century. These results provide evidence that Carmine shiner may be highly vulnerable to a warming climate and suggest that management actions - such as assisted migration - may be needed to mitigate impacts from climate change and ensure the long-term persistence of the species.