Effects of coalbed natural gas development on fish assemblages in tributary streams in the Powder River Geologic Basin, Wyoming and Montana

Coalbed natural gas (CBNG) development in the Powder River Geologic Basin (PRGB) has resulted in disposal of large quantities of product water, which may affect aquatic ecosystems. We used treatment and control, historical comparisons, surveys of CBNG product-water streams, and in-situ survival approaches to determine if CBNG development affected fish assemblages in the PRGB. Certain results suggested that CBNG development had not had a negative effect on fish assemblages. Species richness, biotic integrity, and habitat were similar in streams with and without CBNG development. Fish species richness did not differ significantly from 1994 to 2006 in historical comparisons of CBNG-developed and undeveloped streams. Although overall biotic integrity declined from 1994 to 2006, declines occurred at most sites, likely as a result of long-term drought. Fish occurred in streams that were composed largely or entirely of CBNG product water. Other evidence suggested that CBNG may negatively affect fish assemblages over time. Conductivity was on average higher in treatment streams and was negatively related to biotic integrity. Bicarbonate, the primary salt in product water, was higher in developed streams and may have limited abundance of longnose dace. Our study was limited by a paucity of pre-development data, unquantifiable product-water discharges, and drought.