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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In general, wetlands with single breaches (Stirrup, L-7, Stewart Lake with the outlet

closed) entrain water only during increasing flow stage, compared to multiple breach wetlands

such as Thunder Ranch, Bonanza Bridge, and Above Brennan, which entrain flow at all river

stages when breaches are inundated. Entrainment of razorback sucker larvae is likely much

higher over a season in a flow-through wetland because water is flowing through at all times.

Single breach wetlands receive inflow only when filling, so relatively fewer razorback sucker

larvae would be entrained. The sporadic, pulsed, and unpredictable nature of razorback sucker

reproduction suggested that wetlands that entrain water throughout the reproductive period for

razorback suckers would have highest entrainment rates of larvae.

It is possible that larvae, once entrained into a flow-through wetland, could be transported

through it and back to the river, thereby resulting in reduced net entrainment rates. We did not

sample outflows of flow-through wetlands during this study so we can not directly estimate exit

rates of beads or larvae. However, we think loss oflarvae to the flood plain outflow following

entrainment is low because flood plain wetlands likely act as a filter and depositional area for

particles (flood plains are depositional by definition), including beads and larvae. This is

because breach sites are long distances from outflows, and the intervening area, the main body of

the wetland, is typically large, structurally complex with vegetation and other velocity breaks,

and has very low current velocity. In the main wetland area, fish larvae are likely capable of

finding low velocity refuges and are able to remain there even during higher flows, because the

wetland area and low velocity channel margin and benthic areas also expand. Velocity tube

swimming experiments have shown that razorback sucker larvae the size of individuals that are

typically available for entrainment into flood plain wetlands (9-12 mm TL) are capable of

swimming up to 15 cm/sec for 5-15 sec, and are capable and persistent swimmers at lower water

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