9508

• UCREFRP Catalog Number: 9508
• Author: Valdez, R. A. and P. Nelson.
• Title: Green River Subbasin Floodplain Management Plan.
• USFW Year: 2004.
• USFW - Doc Type: Lakewood, Colorado.
• Copyright Material: NO

3.0 Scientific Basis And Underlying Principles

3-15

April 2004

The geomorphic and hydrologic characteristics of given floodplains that maximize larval
entrainment are not well understood. It is assumed that drifting larvae are randomly mixed in the
river water column and that those floodplains that receive the greatest water volume entrain the
greatest numbers of larvae. Studies of drifting surrogate species and artificial beads indicate that
these assumptions may not be correct. Numbers of drifting larvae of flannelmouth sucker and
bluehead sucker in the Upper Colorado River were greater along shorelines than in the central
channel (Valdez et al. 1985). Preliminary studies with artificial beads also indicate that particle
distribution may not be random (Personal communication, Kevin Christopherson, Utah Division
of Wildlife Resources), and that larval entrainment at a given floodplain may be a function of
local geomorphic features (e.g., sand bars, position of floodplain in river bend, number and
position of levee openings) and river hydraulics (e.g., local currents, diel river surges). Studies
may be necessary to better understand drift and entrainment characteristics of larvae in order to
better design floodplain sites.

3.7.3 Sufficient Food Production

Most floodplains produce an abundance of food for fish in the first few months of
inundation, although the amount of food produced may vary with floodplain site (Crowl et al.
2002; Gourley and Crowl 2002). Timing of inundation and chronology of food production is
critical to growth and survival of entrained larvae. Production in floodplains occurs as a
chronology of communities that begins with inundation of dry floodplains and the appearance of
rich detrital loads, diatoms, and algae. This is followed by emergence of various zooplanktors,
such as rotifers and copepods, that transition into larger forms including cladocerans and various
insect larvae (Mabey and Shiozawa 1993; Modde 1997; Crowl et al. 2002; Gourley and Crowl
2002). Rich detritus and invertebrates are important food sources for young fish (Papoulias and
Minckley 1990, 1992), and the timing of their appearance with the entrainment of larvae in these
floodplains is critical to larval survival (Wydoski and Wick 1998). Larval razorback sucker pass
through a "critical period" when nutrition shifts from endogenous (yolk) to exogenous
(zooplankton) sources at between 8 and 19 days of age, and they require immediate sources of
moderate to high food densities to avoid starvation (Papoulias and Minckley 1990, 1992; see
section 3.5).

3.7.4 Suitable Quantity and Quality Of Water

Depression floodplains must have sufficient depth to maintain suitable water quantity and
quality for fish to survive during hot summer days and cold winters for at least 1 year. Some
depression floodplains may be perched (i.e., elevation higher than the river bed) and maintaining
water in these will require excavation to offset evaporative losses, high water temperatures, low
oxygen, and complete ice formation in winter. Other depression floodplains may receive surface
inflow or seepage that will help to freshen water quality, moderate temperatures, and prevent
total freezing. Suitable water quality in these floodplains is critical to insure maximum fish
growth and survival.