Niobrara-Missouri River Fishery Investigations

The Niobrara River heads in the table lands of eastern Wyoming and flows 786 kilometers (km) eastward across Nebraska joining the Missouri River near the town of Niobrara, Nebraska. The Niobrara is the largest Missouri River tributary between the last two mainstem impoundments (Lake Francis Case and Lewis and Clark Lake). Fish movement up the Niobrara is prevented by Nebraska Public Power District\u27s (NPPD\u27s) Spencer Hydroelectric Dam, 63.3 km upstream from the river mouth. The lower reach of the river is turbid and carries a considerable load of sand, silt, and organic debris into the Missouri River. The mean annual flow is 49.5 m3/s. The mean annual flow through Spencer Dam for the period September 1976 through September 1977 was 37.7 m3/s. Silt, sand, and debris settle into the reservoir behind Spencer Dam. Periodic flushing is needed to prevent damage to the turbines. Quarterly flushings have resulted in significant fish kills downstream from Spencer Dam (Hesse 1976, Hesse 1977, Wallace 1976). Niobrara River fish populations have not been studied previously. In contrast, the fishery of the Missouri River-L.ewis and Clark Lake system was studied by the U.S. Fish and Wildlife Service from 1962- 1974 (Walburg 1976). Walburg alluded to the beneficial relationship that potentially exists between the Niobrara and Missouri river systems. The fishery in Lewis and Clark Lake has been declining since 1959 for reasons that are well defined (Walburg 1964, Walburg 1976). The Niobrara is a major tributary and may offer a better spawning and nursery environment than the Missouri-Lewis and Clark system. This study was designed to distinguish the relationship existing between the fisheries of these two systems and establish a baseline of life history data for Niobrara fishes for future reference. This information is especially valuable, since proposals by the U.S. Bureau of Reclamation would create an impoundment on the Niobrara (O\u27Neill-Norden Dam Irrigation Project) approximately 208 km upstream from the mouth of the river. Should this project become reality, flows in the Niobrara at Norden, Nebraska, would be reduced from the 21.9 m3/s mean annual flow for the period 1964-73 (Nebraska Natural Resources Commission 1976). Projected flow through Norden Dam would be 5.7 m3/s for 60% of the time {personal communication with Roger Andrews, U.S. Bureau of Reclamation). Reduced flow will surely restrict fisheries habitat in the lower Niobrara. If the Niobrara River is a significant contributor to the fishery of the Missouri River - Lewis and Clark Lake system, a loss of fish habitat in the Niobrara could have a detrimental effect on the fishery of the larger system. Collection of data at this time will aid in the assessment of such losses if they occur