Development of Field Sampling Methods to Estimate Rates of Fish Stranding Caused by Operational Flow Ramping
Flow reductions from dams can strand fish and other aquatic organisms along the shoreline or in side channels. This research will determine if sampling methods can be developed to precisely estimate rates of fish stranding in stream reaches affected by Reclamation projects. Such methods could be used to assist managers in developing operational procedures that minimize stranding of protected species.
Need and Benefit
Reclamation operations frequently change the water level near dams and diversions, which can strand fish along the shoreline or in backwaters. Because threatened or endangered species reside in many streams affected by Reclamation operations, state and federal regulatory agencies have sometimes mandated the maximum rates at which Reclamation can change water levels (i.e., ramping rates). However, no applicable data exist with which to set ramping rates for some projects, and Reclamation is being required to develop scientifically justifiable ramping procedures to avoid interruptions in water delivery.
For example, Reclamation will be required to develop appropriate ramping rates for the Yakima River Basin to avoid placing federally threatened Middle Columbia River steelhead _Oncorhynchus mykiss_ populations in jeopardy. Because previous studies of fish stranding were designed to answer slightly different research questions, they provide relevant information but do not provide appropriate designs for studying ramping rates at Reclamation projects.
Most studies reported in the literature have taken one of two approaches to quantifying fish stranding. First, some studies have used laboratory or flume experiments to quantify the effects of specific factors such as temperature, light level, or ramping speed on stranding rates. These studies are useful to determine the relative importance of the factors tested but are too artificial to be compared directly to natural streams affected by Reclamation operations. Second, some field surveys have used simple counts of fish stranded along dewatered reaches. Although these studies provide an index to the number of fish stranded, they underestimate the number because fish that are trapped in interstitial spaces in the gravel are not observed. Furthermore, this type of stream survey provides no estimate of the uncertainty of the index. This research will develop methods quantify stranding rates in natural streams that are affected by Reclamation operations, and also provide valid estimates of precision (i.e., confidence intervals).
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