7796

• UCREFRP Catalog Number: 7796
• Author: Burdick, B. D.
• Title: Conceptual Management Plan for Habitat Enhancement in Flooded Bottomlands, Escalante State Wildlife Area, Gunnison River Downstream of Delta, Colorado.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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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" the timing of the swim-up stage of fish
larvae. After the yolk sac absorbs, food organisms of the right size must be
available to fish larvae or they will starve. This principle was suggested by
Marsh and Langhorst (1988) for wild razorback sucker larvae in Lake Mohave and
documented for the razorback sucker larvae in the laboratory (Papoulias and
Minckley 1990). Razorback sucker larvae of about 10 mm total length were
maintained in the laboratory at 18°C. Unfed razorback larvae died in 10 to 30
days. Razorback larvae must find food of the right size and density in 8 to 19
days to survive. The "point of no return" when the fish died even though
sufficient food of the right size was available was between 19 and 23 days for
razorback sucker larvae. Papoulias and Minckley (1990) reported that the
quantity of food required for survival of the razorback larvae was 20 brine
shrimp nauplii per fish or high mortality occurred.
Food Availability for Larval Endangered Fishes in the Uaper Colorado River
Basin. The larvae of all endangered Colorado River fishes feed on zooplankton
early in life (USFWS 1987, 1990a, 1990b, 1991). The first foods of larval
razorback suckers in ponds were diatoms, detritus, algae, and rotifers (Papoulias
and Minckley 1992). Soon afterward, the razorback larvae began to select larger
organisms such as zooplankton (primarily cladocerans). The density of
zooplankton needed for larval razorback sucker survival (20 organisms per liter
of water; Papoulias and Minckley 1990) occurred in flooded bottomland habitats
along the Green River but rarely reached that density in backwaters, and never
reached it in the river (Mabey and Shiozawa 1993). The decline in razorback
sucker and the near extirpation of the bonytail (G. elegans) in the upper basin
may be linked directly to low or lack of larval survival in these species.
Therefore, flooded bottomland habitats are important to some, if not all, of the
endangered Colorado River fishes in the upper basin. Zooplankton produced in
productive off-channel habitats such as flooded bottomlands also provide food of
the proper quantity and size at the right time needed for larval survival of
endangered fishes that occupy main channel habitats such as the Colorado
squawfish and humpback chub (G. cypha).
PROPOSED DEVELOPMENT/ACTION
General
The CDOW, a member of the Recovery Program, has agreed to participate and
assist in developing habitat restoration strategies that will aid the recovery
of endangered fish species in the upper Colorado River basin. The overall
strategy at the Escalante SWA must include habitat restoration that benefits
other aquatic as well as terrestrial fauna that utilize riparian corridors.
Although CDOW personnel are supportive of this endeavor, they have emphasized
that the original management objectives of the property cannot _be adversely
impacted by proposed development. Their requirements are:
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