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Dam, That’s A Lot of Crayfish: Assessing the Effects of Impoundments on Northern New York Streams
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Fall 2025
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2025-12-11
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Stream impoundments shape habitat structure, water quality, and biodiversity. We aimed to evaluate the impact of impoundments and subsequent changes in stream substrate structure on crayfish communities. In fall 2025, we surveyed crayfish communities in both the Salmon and Little Ausable Rivers. At both sites, crayfish were identified and measured along with water quality (e.g., pH, conductivity, and temperature). Crayfish communities were similar along the Salmon and Little Ausable Rivers, while eastern crayfish (Cambarus bartonii) were unique to the former. Above the Salmon River impoundment (lentic), large rocky substrate resulted in a dominant species of big water crayfish (C. robustus) (S=1) who were larger and had symbiotic (Branchiobdellida) on their carapaces. Below the dam (lotic), species richness was highest (S=3) consisting of northern clearwater (Faxonius propinquus), spinycheek (F. limosus), and smaller eastern crayfish. Upstream on the Little Ausable River, crayfish were higher in abundance and dominated by big water with some clearwater crayfish (S=2), while the downstream community contained only a few spinycheek crayfish (S=1). Conductivity and pH on the impounded Salmon River increased downstream; however, on the Little Ausable River (unimpounded) the conductivity and pH were similar up and downstream. Crayfish communities differ along river gradients, which supports our findings that communities up and downstream along both rivers were unique. Crayfish are robust to changes in water quality; however, changes in habitat structure can be more consequential. At the Salmon River impoundment, stream substrate was primarily large rocks creating deep water reducing predation risk. Big water crayfish are large and often live in fast flowing rocky streams which explains their absence at the dammed site. Crayfish observed below the dam were smaller, possibly due to low stream depth and reduced substrate size. There was a greater abundance upstream at the Little Ausable, where spinycheek crayfish are more adaptable to microhabitats. Crayfish abundance was higher on an unimpounded stream which suggests impoundment-induced changes may limit their abundance. Dams are both essential infrastructure that reduce rusty crayfish (F. rusticus) invasion risk, while at the same time they can change riverine conditions that displace sensitive crayfish species.