Biologist Brad Anderson observes a flooded wetland from his canoe

Tildon Jones, Upper Colorado River Endangered Fish Recovery Program
February, 2020

Over the last decade, floodplain wetlands have become an essential part of endangered species management. It has long been suspected that warm, food-rich floodplain wetlands were key to certain life stages of razorback sucker. Larval, or baby, fish in the wetland are protected from large-bodied predators and have plenty of food to eat. Floodplain wetlands are only accessible by fish during the spring runoff period when the river swells with snowmelt and floods the wetlands. Since the construction of Flaming Gorge Dam, an on-channel reservoir located on the Utah-Wyoming border, the Green River experienced fewer years when wetlands connected to the river. In an attempt to reconnect these habitats for endangered fish, the Bureau of Reclamation released flows out of Flaming Gorge Dam to match the peak of the Yampa River, but fish were still not routinely found in those wetlands. That changed in 2012 with the Larval Trigger Study Plan (see Milestones in Recovery on pages 22-23). Using annual monitoring data, scientists developed a hypothesis that flows were not being released at the right time because razorback sucker larvae were not yet present in the river when flows increased.

Dam releases are now delayed until razorback sucker larvae are found in the river channel. This simple change has produced dramatic results. Stewart Lake, managed by Utah Division of Wildlife Resources (UDWR), became the first gated wetland to regularly produce fingerling razorback sucker. Over the last few years, UDWR biologists have documented the survival of four Stewart-raised razorback sucker to three years of age – the first documentation of natural recruitment to an adult life stage in the upper Colorado River basin. The floodplains also seem to benefit other endangered species. In 2015, bonytail spawned in Stewart Lake, the first documented occurrence of reproduction for that species in the Basin. Prior to 2015, wild reproduction of bonytail had not been documented for decades. Bonytail reproduction has been observed in wetlands four more times since 2015.

After the success at Stewart, the Upper Colorado Program continues to develop floodplain wetlands that are gated and screened to make sure that we can manage both flow and nonnative predators. Capital construction funds are essential to build the gate structures that keep out large-bodied fish and keep water in the wetlands. There are currently four such wetlands in operation along the banks of the Green River, including: Johnson Bottom, Old Charley, and Sheppard Bottom. The Nature Conservancy and UDWR just completed construction on Matheson Wetland, the first wetland of this kind on the Colorado River. In addition, there are several more wetlands along the Green River that can provide habitat, but are not intensively managed.