Long-term fish assemblages of the Ohio River: altered trophic and life history strategies with hydrologic alterations and landuse modifications

Abstract

17Long-term monitoring of species assemblages provides a unique opportunity to test 18 hypotheses regarding environmentally-induced directional trajectories of freshwater species 19 assemblages. We used 57 years of lockchamber fish rotenone and boat electrofishing survey data 20 collected by the Ohio River Valley Water Sanitation Commission (ORSANCO) to 21 test for directional trajectories in taxonomy, trophic classifications, and life history strategies of 22 freshwater fish assemblages in the Ohio River Basin. We found significant changes in taxonomic 23 and trophic composition of freshwater fishes in the Ohio River Basin. Annual species richness 24 varied from 31 to 90 species and generally increased with year. Temporal trajectories were 25 present for taxonomic and trophic assemblages. Assemblage structure based on taxonomy was 26 correlated with land use change (decrease in agriculture and increase in forest). Taxonomic 27 assemblage structure was also correlated with altered hydrology variables of increased minimum 28 discharge, decreased fall rate, and increased rise rate. Trophic composition of fish catch 29 correlated with land use change (decrease in agriculture and increase in forest) and altered 30 hydrology. Altered hydrology of increased minimum discharge, increased fall discharge, 31 decreased base flows, and increased number of high pulse events was correlated with increased 32 counts of herbivore-detritivores and decreased counts of piscivores and planktivores. We did not 33 find directional changes in life history composition. We hypothesized a shift occurred from 34 benthic to phytoplankton production throughout the basin that may have decreased secondary 35 production of benthic invertebrates. This may also be responsible for lower trophic position of 36 invertivore and piscivore fishes observed in other studies. 37 38 3 39 Introduction 40 Anthropogenic threats to freshwater ecosystems are numerous and globally widespread. 41 Rivers are altered by multiple factors including watershed land use, hydrologic alterations, 42 municipal and industrial effluent, and water withdrawals [1]. Conservation of water resources 43 and increased water demands requires understanding historical and current effects of water and 44 land use to help inform potential solutions via restoration or intervention [2]; key to this is the 45 scale at which human activities affect biodiversity, and the patterns detectable across scales. 46 Long-term monitoring data of biotic and abiotic factors, such as fish assemblages, provide an 47 opportunity to test hypotheses regarding how environmental modifications affect the taxonomic, 48 trophic, and life history compositions of aquatic organisms [3,4]. 49 Land use changes from natural ecosystems to those dominated by intense agriculture, 50 deforestation, or urbanization can dramatically alter fish biodiversity [5-7]. Modification from 51 forest, grasslands, or wetlands to tillable agricultural land on a global scale provides numerous 52 benefits to humans. However, these activi...

Temporal dynamics of freshwater fish assemblages, their background and methods of quantifications—A synthesis

“…Choosing the appropriate time scale on which assemblage organization is interpreted is thus a key factor. Since many freshwater fishes are considered to be long-lived, long-term studies and monitoring programs are especially important for a more complete understanding of their temporal dynamics (Comte et al, 2021;Pyron et al, 2019). Matthews et al (2013) supported…”