7799

• UCREFRP Catalog Number: 7799
• Author: Modde, T. and D. Irving.
• Title: Conceptual Management Plan for Habitat Enhancement In Old Charley Wash.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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the density of planktonic crustaceans (cladocerans and copepods) averaged about 36 organisms per liter

during the summer of 1993 (Cooper and Severn 1994a). Cooper and Severn reported a mean of 2

organisms per liter for backwater sites and a mean of 36 organisms per liter for open water wetlands.

Samples of planktonic crustaceans (c1adocerans and copepods) from the Escalante Ranch site on the

middle Green River, upstream from Jensen, Utah, contained 0 organisms per liter for the main channel, a

mean of 41 organisms per liter for backwaters, and a mean of 71 organisms per liter for an open water

wetland (Cooper and Severn 1994b). The mean number of cladocerans and copepods from a backwater

of the Gunnison River at the Escalante State Wildlife Area, about 5 miles downstream from Delta, Colorado,

was 11 organisms per liter of water and the mean number from an open water wetland was 25 organisms

per liter (Cooper and Severn 1994c). Zooplankton (cladocerans and copepods) samples from a bottomland

(Old Charlie Wash) on the Ouray National Wildlife Refuge contained a mean of 31 organisms per liter of

water (Cooper and Severn 1994d). Samples taken from the middle Green River and a backwater on the

refuge did not contain any c1adocerans or copepods.

C. Maior limitinG Factor Affecting EndanGered Colorado River Fish Pooulations. The major limiting factor
affecting the populations of endangered Colorado River fishes is the lack of successful recruitment (U.S. Fish
and Wildlife Service 1987, 1990a, 1990b, 1991). In the Lower Colorado River Basin, studies have
demonstrated that predation by non-native fishes and the lack of food may be limiting the survival of larval
and juvenile endangered fishes (Marsh and Langhorst 1988; Papoulias and Minckley 1990, Papoulias and
Minckley 1992). Similar conclusions have been reached for the endangered Colorado River fishes in the
upper basin (Miller et al. 1982; Maddux et al. 1993).

D. Relation of Food to Larval Fish Survival. Year-class strength of marine fisheries is often related to the

Match or Mismatch Principle where environmental conditions such as water temperature as well as the

quality and quantity of food organisms must match the hatching of larval fishes to realize high survival (Hjort

1914, 1926). In other words, the density, size, time and duration of availability of zooplankton must "match"