Impacts of dewatering and cold on freshwater mussels (Unionidae) in B. A. Steinhagen Reservoir, Texas

This study examined mortality among freshwater mussels (Family Unionidae) associated with dewatering and cold temperatures in B. A. Steinhagen Reservoir of the Neches River drainage of southeast Texas. This reservoir, which supports one of the largest and most diverse mussel assemblages in the state, was examined during normal pool levels in May of 1993. The area was reexamined following partial drawdowns (used to control noxious growths of aquatic macrophytes) in December 1993, January and February 1996, and January 1999. Immediately following the January 1996 examination, record cold air temperatures, while water levels were about 2 m low, resulted in air temperatures at or below freezing for six consecutive nights and four overcast days, including two nights below -5°C. When the site was examined several days later, all unionids above the water line were dead. Only those individuals which followed the declining water line or remained in deeper waters survived. A survey during the subsequent drawdown in 1999 found overall mussel abundance reduced, but confirmed nearly all taxa originally documented were still present and most had successful reproduction since the 1996 mussel losses.