Threats to Wildlife and the Platte River

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p. 38 WILDLIFE believing it inadequate because some fish kills have occurred when flows at gauging stations were as high as 500 or 600 cfs (R. Lock 1988, pers. comm.). New models for fish suggest that summer flows of 750 cfs may be required to maintain fish populations during all phases of their life stages. In these preliminary models, 750 cfs yields highest suitability. In other words, the most habitat occurs at that flow during the summer. S J. VanDerwalker (1987, pers. comm.) emphasizes that these are relatively "soft" estimates, pending further results. It has been noted that Least Terns require braided river morphology for successful nesting. They may also require the shallow water areas, which are present in a braided river, to allow them adequate access to fish. These fish may be unavailable to them in deeper channels and pools. "Lentic systems, such as sandpits, apparently are little -used by foraging terns" (USFWS 1987b, p 25). T A balance is sought that would allow the birds to nest without flooding of their sandbars, while at the same time allowing the existence of a maximized water barrier to terrestrial predators and humans. "Most of the human- caused losses of both eggs and chicks were attributed to all- terrain vehicles... Recreational disturbances of a nesting colony [occurred while nearby flows were gauged at] 633, 564, 636, and 715 cfs... Attempts to deter human disturbance at nesting colonies involving posting... patrol... personal contact..., and newspaper notices, have generally been ineffective..., and efforts to apprehend perpetrators have been unsuccessful. The most effective method to reduce or prevent disturbance of nesting piping plovers and least terns appears to be providing the necessary flows that will allow for isolated and protected nesting habitat... Predation at sandbar colonies... has been observed during flows as high as 1,810 cfs. Predator disturbance to river colonies can be expected to increase as flows are reduced and as access to the river channel increases... All of the instances related above involving human disturbance of nesting sites occurred when flows levels were below 800 cfs. Therefore, the Service believes that a flow level of at least 800 cfs should be maintained in the central Platte River system each year between the dates May 15 and September 15" (USFWS 1987b, p 24). Tern nesting has been initiated at flows between 2,370 cfs and 3,500 cfs, while inundation of nest sites has occurred at flows between 3,000 and 4,700 cfs. "Therefore, the Service believes that maximum daily flows of 2,500 cfs should not be exceeded in the central Platte River during the principal nesting period from June 1 to August 25" (USFWS 1987b, p 25)." U "The Service has accepted the determination of the NGPC that a minimum flow of 400 is needed during non - summer periods to sustain and provide for the reproduction and survival of forage fish populations" (USFWS 1987b, p 26). The rationale for accepting different flows for summer and non - summer is not explained, although it is briefly mentioned that temperature extremes, low flows and accompanied "changes in physical, chemical, or biological factors, can adversely impact fish populations... A recent fish kill occurred when summer flows ranged between 400 and 800 cfs. Therefore, a minimum flow of 800 cfs is considered necessary to sustain fish habitats during the period June 1, to September 15" (p 26). Whether the low flow or seasonal factors such as temperature contributed more to this die -off is not addressed.