9641

• UCREFRP Catalog Number: 9641
• Author: Hedrick, T. N., K. R. Bestgen and K. D. Christopherson.
• Title: Entrainment of Semi-Buoyant Beads and Razorback Sucker, Xyrauchen texanus, Larvae into Flood Plain Wetlands of the Middle Green River, Utah.
• USFW Year: 2009.
• USFW - Doc Type: C-6/RZ-ENTR,
• Copyright Material: NO

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were released upstream of Breach 3 at Thunder Ranch (Figure 4), which nearly coincided with

the location of the Escalante spawning bar. Four drift nets were set in Breach 3, four in Breach 5

(which has a slightly higher river stage connection than 3), and four downstream from Breach 5

on the near shore. Drift nets sampled all or nearly the entire breach water column because

breach depths were typically shallow; depth of flow sampled was noted for all net sets. All drift

nets were again equipped with a GO Model 203 OR mechanical flow meter suspended in the

center of the net to determine flow velocity and ultimately, the amount of flow being sampled. If

flow readings appeared incorrect (i.e., the end number was less than the beginning number),

crews noted the inaccuracy on the data sheet and replaced the flow meter. Depth and flow

measurements were also taken across a breach transect to estimate flow entrainment rates. If the

water stage in the breach was more than 1.5 cm different from the start to the finish of sampling

(generally a two to three hour timespan), depth and velocity measurements were taken again at

the end of the sampling period.
Due to difficulties noted in 2005 with the GO flow meters, crew members also took flow

readings at the mouth of each net using the Marsh-McBirney flow meter on most sampling

occasions (13 of 18 occasions at all sites, breaches, and dates; net readings were taken at both

breaches on all Thunder Ranch sampling dates [n = 7] except on 21 May in Breach 3). Because

of the overwhelming number of problematic GO readings, we used only Marsh-McBirney meter

readings when available or transect-estimated net velocities (explained below) to calculate water

velocity at drift net mouths and the amount of water sampled. Where Marsh-McBirney meter

readings were taken to replace GO meter readings, they were taken only once at each net per

sampling occasion; that velocity was assumed to be the mean velocity of water flowing into the

net over the sampling period.

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