Quantifying Flows Through the Fort Peck Dam Project Was Easy, What about the Fish?

Fort Peck Reservoir is known for its trophy walleye Sander vitreus fishery, while the fishery in the Missouri River downstream of the dam is dominated by sauger S. canadensis.  Historic flows in the upper Missouri River during 2011 forced water to be released over the Fort Peck spillway for the first time since 1997. At its peak, 53,000 cfs was bypassed over the spillway, while an additional 13,700 cfs was passed through the powerhouse, which is situated 8 river miles upstream.  In addition, historic flows occurred in the Milk River, a large tributary to the Missouri River that enters the Missouri River one mile downstream of the spillway.    Sampling regimes have been in place on both the reservoir and river with the objective to monitor trends in relative abundance and size structure of walleye and sauger, as well as other game and non-game fishes.  However, due to the complex nature of the system as a whole in a water year like 2011, understanding the extent of fish entrainment through Fort Peck Dam and how entrainment might affect both fisheries is exceedingly difficult.  Traditional sampling regimes are likely sufficient to detect entrainment, but may not be suitable for quantifying its extent. Therefore, a specific study design may need to be in place prior to a spill event if managers are going to fully understand entrainment and its effects on the fishery.