Responses of fish assemblages to changing environmental conditions in the Neversink River and Rondout Creek

Problem

The Neversink River and Rondout Creek are historic trout fishing and recreational streams in the heart of the Catskill Mountains of southeastern NY. Waters throughout upper reaches of both rivers currently range from neutral to severely acidic due to deposition of acid rain throughout their watersheds. Fish surveys conducted by the USGS during the late 1980s and early 1990s found that some fish species and entire assemblages were absent or depressed in many tributaries and second and third order reaches of both rivers. Recent decreases in acidity of atmospheric deposition and changes in hydrologic and thermal regimes are now affecting water chemistry (e.g., pH, acid neutralizing capacity, dissolved organic carbon, and inorganic Al concentrations) and habitat quality which govern the distributions of resident fish species. Warmer stream temperatures and more extreme high and low flow events may also threaten stream ecosystems in the future. Shifts in thermal and hydrologic regimes will obviously favor some fish species, adversely affect others, and strongly influence local fish communities across both rivers. For example, competitive interactions between the native eastern brook trout and non-native, naturalized brown trout (less tolerant of low pH than brook trout) are expected to increase and will likely further reduce the local distributions of brook trout. Unfortunately, the current status of resident species populations and fish communities, the key factors which regulate the distribution of important species, the extent to which fish assemblages have recovered from decreases in acidification, and the potential impacts that changing hydrologic and thermal regimes might have on fish assemblages throughout both rivers is largely unknown. 

 Objectives

The U.S. Geological Survey (USGS), in cooperation with the New York City Department of Environmental Protection (NYCDEP) and the Sullivan County Soil & Water Conservation District (SCSWCD), proposes to survey fish assemblages across both rivers during 2017-19. The main objective of this study is to increase our understanding of present-day fish resources and the factors which regulate species distributions in the Neversink River and Upper Rondout Creek. Specific goals of this investigation are to: (a) develop a contemporary baseline for fish resources in order to gauge future trends and changes, (b) quantify the spatial and temporal variability in local fish populations and communities, (c) assess the current interrelations among fish metrics and acid-base chemistry, and (d) document the extent that fish assemblages may have recovered from recent reductions in acid deposition and stream acidification.

Approach 

Fish assemblages will be quantified and base-flow (summer) water quality (chemistry) will be analyzed annually at approximately 20 sites (total) in the two rivers during a 3-year study period. The same sites sampled during the late 1980s and early 1990s will be targeted where possible to enable an analysis of potential recovery in fish assemblages associated with decreases in stream acidification. Two comparable fish survey techniques will be used to quantify fish assemblages at small- and large-channel study sites (reaches), respectively. In narrow channels (<15 m), blocking seine nets will be placed completely across the channel at the upstream and downstream end of study reaches. At sites with wide channels (>15 m), three replicate surveys will be conducted in smaller near-shore sub-reaches blocked with one 30 m-long longitudinal seine and perpendicular upper and lower blocking seines. Fish will be collected with a backpack electroshocker using a 3-pass depletion method, and three to four people netting all stunned fish. A maximum likelihood population estimator will be used to estimate population sizes and biomass. These values will be standardized by area to produce estimates of density and biomass (and 95% confidence intervals about each) for each species and the entire community. Within each reach and sub-reach, dominant substrate, depth, velocity, and width will be measured across 10 transects as well as the total reach length (in order to calculate reach area). A stream discharge measurement will also be taken at all ungaged sites. Water chemistry samples will be collected once each summer at all study sites and will be analyzed for pH, acid-neutralizing capacity (ANC), SO₄^2-, NO₃^-, NH₄⁺, chlorine (Cl^-), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), silica (Si), potassium (K⁺), dissolved organic carbon (DOC), total Al (Alt), total monomeric Al (Al_tm), and organic monomeric Al (Al_om); at the USGS laboratory in Troy, NY. Concentrations of inorganic monomeric Al (Al_im) will be calculated as the difference between Al_tm and Al_om concentrations. Chemistry data will be used to (a) characterize present-day water quality, (b) provide a foundation for assessing changes from past conditions, and (c) analyze and interpret relationships between acid-base chemistry and fishery metrics.

 Project Location by County

Ulster County, NY, Sullivan County, NY, Delaware County, NY