Is the Yellowstone-Sakakawea paddlefish population increasing or decreasing?

The paddlefish population in the Yellowstone and Missouri rivers prior to construction of Garrison Dam was much smaller than the booming population which developed during the years when Lake Sakakawea first filled. Initial flooding of productive uplands released many nutrients into the newly formed reservoir, resulting in excellent rearing conditions and high survival of young paddlefish. In the years since the late 1960s after the reservoir filled, however, the population has gradually declined because of lower productivity (a natural process in reservoirs), and harvest and natural mortality of fish produced during the filling period.

Population estimates indicate that the adult population has declined from more than 100,000 fish in the late 1970s to somewhat less than 50,000 in recent years. Studies have shown that although paddlefish reproduction is occurring, the overall recruitment of young fish hasn’t been high enough to offset mortality of adult fish. Fortunately, the 1995 year-class has reversed the downward population trend. This robust year-class was produced under ideal conditions of high Yellowstone River flows and rising water levels in Lake Sakakawea. From 1999 through 2007, drought and water depletions greatly reduced Yellowstone River flows, negatively affecting paddlefish spawning and reproduction. The lower than normal inflows, coupled with excessive rates of water discharge by the U.S. Army Corps of Engineers, consequently lowered Lake Sakakawea’s water level far beyond that desired for good paddlefish recruitment and growth. Greatly improved water flows and lake levels since 2008 have provided better conditions for successful reproduction and recruitment, especially in 2011, which appears to be providing the next large year-class of paddlefish.