Have Adirondack Stream Fish Populations Changed in Response to Decreases in Sulfate Deposition?

Fish populations in 36 Adirondack headwater streams were surveyed by electrofishing in fall 1979 and 1999; water chemistry samples were collected during spring 1980 and 2000. The surveys were designed to evaluate impacts of acidity on stream fish populations and also to document any changes that had occurred between the two studies. The acid‐neutralizing capacity and pH of the streams were not significantly different between 1980 and 2000, although in a different grouping of 37 Adirondack streams, calcium levels were significantly lower in spring 2000 than in spring 1982. More fish and fish species were collected in 1999 than 1979. However, because changes occurred in streams with relatively high pH (>6.0) as well as in low‐pH streams, increases in fish caught may have been partly the result of improved electrofishing efficiency in 1999. In both 1999 and 1979, streams with spring pH less than 5.0 supported fewer fish, fewer salmonids, and fewer fish species than streams with higher pH. No young‐of‐year brook trout Salvelinus fontinalis were found in streams with a spring pH less than 4.98. Sensitive and acid‐impacted streams continue to exist in the Adirondack region even though sulfate deposition has decreased since the 1990 Clean Air Act Amendments.