Above-average fluctuations in rainfall, snowmelt and runoff in the lower Missouri River are complicating U.S. Fish and Wildlife Service efforts to recover endangered pallid sturgeon, one of the continent’s largest freshwater fish. Unusually low water levels in 2004 and 2006 have been followed by record high levels since 2007, say scientists. The Service is working with the U.S. Geological Survey (USGS) through the National Climate Change Wildlife Science Center and Science Support Partnership Program to anticipate how a range of such changes may impact pallid sturgeon recovery efforts throughout the region, encompassing Missouri, Nebraska, Iowa, Kansas and South Dakota.
“Essentially we are trying to build a more comprehensive picture of how the fish may react [to changes in water level and temperature that might be associated with a changing climate],” said Mark Wildhaber, USGS research ecologist.
For centuries, rivers in the West and Midwest teemed with these great fish, which can weigh as much as 60 pounds, and have distinctive long, flat snouts. Then engineers dammed and straightened the Missouri, eliminating tree snags where sturgeon would feed, hide and spawn. Overharvesting by commercial roe fishermen further stressed the species, listed as endangered in 1990. Scientists have only recently begun to factor climate change into the recovery equation.
Wildhaber is working with researchers from the University of Missouri and Iowa State University to build complex computer models that examine the potential impacts of varying precipitation, water flow and water temperature on the watershed, river hydraulics and fish populations.
For sturgeon, some potential changes are double-edged swords. Higher water temperatures, for example, would raise fish metabolism, spurring growth and reproduction — as long as adequate food is available. If food is scarce, however, fish growth and reproduction would likely slow in warmer water.
High water flow can likewise help or hinder sturgeon recovery. In spring, high flow benefits the fish, triggering migration and conditioning spawning sites. But in summer, high flow washes fry downstream, reducing survival and recruitment into the adult population.
Service biologists are trying to rebuild the pallid sturgeon population through captive breeding. Since 2002, the Neosho National Fish Hatchery has produced more than 27,000 pallid sturgeon and stocked them in the lower Missouri.
The Service and USGS tag all hatchery-raised fish and monitor their survival. But so far, pallid sturgeon populations aren’t bouncing back.
“The million-dollar question is why do we come across hundreds of shovelnose sturgeon [a sister species] and only a single pallid when we are out on the river sampling?” said Tracy Hill, project leader of the Service’s Fish and Wildlife Conservation Office in Columbia, Missouri.
The pallid’s feeding habits could be partly accountable. While shovelnose sturgeon feed primarily on silt plankton and small invertebrates, pallid sturgeon depend on larger organisms, such as other fish, for food. Changes to river habitat and water flow have reduced the availability of those organisms, a situation that could be exacerbated by a changing climate.
Commercial roe fishing is also still a threat. Shovelnose caviar is more sought after, but pallid sturgeon have also been harvested for their eggs. The Service’s recent listing of shovelnose sturgeon as threatened may help protect both species. The listing permits law enforcement actions in portions of the Missouri and Mississippi River basins where pallid and shovelnose sturgeon co-exist.
Recovery scientists meanwhile are trying to plan for an uncertain future. “There isn’t one answer,” Wildhaber said. But he and his colleagues think computer modeling offers them their best shot at adapting wildlife management practices to changing climate conditions.
This story was written by Ashley Spratt for the U.S. Fish & Wildlife Service and is reprinted with permission here.