Relationships between environmental variables and fish functional groups in impounded reaches of the Upper Mississippi and Yangtze Rivers

Large rivers throughout the world have been transformed by anthropogenic stressors that are known to influence the structure and composition of fish assemblages.Management of large rivers requires balancing socio-economic and political considerations with biodiversity conservation efforts.By exchanging best management practices between rivers,management efforts can be improved.However,data limitations have largely prevented comparative analyses among fish assemblages in large rivers,potentially limiting the effectiveness of shared management strategies.To improve understanding of the similarities and differences between the Upper Mississippi and Yangtze Rivers,we(1)compared environmental variables and functional traits of fish assemblages between the two systems,(2)identified traits responsible for distinguishing functional groups from one another,and(3)investigated relationships between similar functional groups of fishes and environmental variables to establish expectations for how fish assemblages in large rivers might respond to anthropogenic stressors.Regional species pools in the Upper Mississippi and Upper Yangtze Rivers were characterized by a similar composition of functional traits;the majority of species were omnivorous,had affinities for gravel or sand substrates,and produced sinking eggs.Few species were pelagic,planktivorous,or herbivorous.Functional groups in both rivers were primarily distinguished according to species'trophic habits and substrate preferences,with secondary contributions from species’water column positions and life history characteristics.Pelagic planktivores and smallbodied guarders with an affinity for structural habitat complexity tended to increase downriver in both systems,in direct association with total phosphorus concentrations,agricultural land use,and temperature.In contrast,proportions of lithophilic species with affinities for gravel or cobble substrates were highest in segments located furthest upriver.By highlighting the sensitivity of different groups of fishes to anthropogenic stressors,we provide insights into the functional ecology of fishes inhabiting the Mississippi and Yangtze Rivers.

Fish diversity reduction and assemblage structure homogenization in lakes:A case study on unselective fishing in China

Unselective fishing involves activities that target the entire assemblage rather than specific fish species,size classes,or trophic levels.This common fishing approach has been in practice for decades in inland waters in China but its implications for biodiversity remain unclear.We addressed this issue by studying fish assemblages in freshwater lakes(five fishing lakes,one reference lake,and a total of 51 sampling sites)between pre-and postfishing time-periods in Eastern China during 2017–2019.The effects of lake,fishing period,and their interactions on fish abundance,biomass,and diversity indices were assessed.Multivariate analysis was conducted to test for differences in fish assemblages among lakes and between fishing periods.After the implementation of fishing activities,significant reductions in fish species richness,abundance,biomass,and all three life-history strategies(opportunistic,equilibrium,and periodic)were observed in fishing lakes,whereas opposite trends were observed in the reference lake.Compositional similarity of fish assemblages among fishing lakes increased over the threeyear monitoring period.Our results suggest that unselective fishing reduces fish diversity and homogenizes fish assemblage structure in lakes.These findings have important implications for protecting both biodiversity and fisheries in inland waters in China and are applicable to other countries or regions that rely on fish as a major food source.

Assemblage-based biomonitoring of freshwater ecosystem health via multimetric indices:A critical review and suggestions for improving their applicability

Freshwater biota are more comprehensive and direct indicators of biological impacts,and more meaningful to the public than water quality or physical habitat surrogates.Freshwater biotic data and the multiple biological indicators developed from them offer a much richer array of data for assessing the impacts of pollution controls than a limited set of physical or chemical measures.In recent decades,assemblage-based assessments by ecologists,environmental scientists,and water quality agencies have been employed globally for determining the condition of,and threats to,freshwater ecosystems.A key step in this advance has been the development of multimetric indices(MMIs)or indices of biotic integrity(IBIs)based on quantitative assessments of algae,macrophyte,macroinvertebrate,fish or riparian bird assemblages.In Europe,where biological assemblages are mandated for assessing freshwater ecosystem health,many indices are multimetric.However,the proliferation of MMIs globally has not always occurred through the application of rigorous study designs and monitoring protocols,nor have they always effectively incorporated functional metrics,stressor assessments,and statistical analyses.Therefore,in this review,we discuss eleven major concerns with the development and application(including logistical limitations)of multimetric indicators based on freshwater biota to encourage more rigorous and widely applicable(transferable)MMI use and implementation.Specifically,our concerns focus on reference conditions;sampling effort,methods,and season;trophic guild definition;metric comprehensiveness,options,screening and scoring;and MMI validation.MMIs could also benefit from increased attention to ecological mechanisms and metric development,to further improve our understanding of anthropogenic impacts as well as rehabilitation effects on freshwater ecosystems globally.Paying closer attention to study designs,ecological mechanisms and metric development should further improve our understanding of anthropogenic impacts and better facilitate rehabilitation of degraded freshwater ecosystems,as well as aiding in the conservation of healthy freshwater ecosystems globally.