8155

• UCREFRP Catalog Number: 8155
• Author: Minckley, W. L.
• Title: Executive Summary
• USFW Year: 1985.
• USFW - Doc Type: Native Fishes and Natural Aquatic Habitats in U.S. Fish and Wildlife Service Region II West of the Continental Divide.
• Copyright Material: NO

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then stocked wi th native species. Dry cuts across oxbows are further a
major method of channel ization in the Region, and seepage through porous
.:illuvium fills depre~.sions e:<c:ivated deeper than the local !,lIater table.

Planning prior to river modifications would al low developmen~ of ma~or
habitat-:. in this manner. Spoil from dredging operations could be u~.t?d to
product? berms to protect isolated water areas from potential flooding and
escape of native fishes or invasion by non-native forms. Securi ty already
existing on many such lands would further assist in maintaining an
uncont~minated native fauna. Water rights for indirect losses through
evaporation could be negotiated or otherwise compensated for by removal of
less desirable (fer example shallower) habitats from use by NWR or other
management entities. Direct costs for such operations could be recovered
as mitigation for river modifications that effect changes in wildl ife and
fish habitats, and additional water areas would benefit waterfowl and other
organisms alrea.dy managed for b:,' the Refuge system.

Such habitats could be large and self-sustaining, or might be designed
smaller and more amenable to direct management such as periodic eradication
of undesirable fishes if they became establ ished. Although these are
obviously habitats of Category VI (artificial refugia), a strong case may
be made for former occupation of oxbows and other cutoff aquatic habitats
along the Colorado River by species now I isted as endangered. The only
differences between excavated and natural depressions are in the mode of
formation. Relatively small ponds or other aquatic habi tats constructed
adjacent to the mainstream or isolated bays of reservoirs as discussed
above could further double as grow-out systems to produce fingerl ing or
larger individuals of native species for periodic release into the river.
Such a combination of semi-natural refuge and production facil ity would be
no more expensive than the second possible alternative, and should be
strongly considered. If a decision is made to maintain Desert pupfish
along the lower Colorado River, alternatives 2 or 3 are highlY appl icable
since that species reproduces pro I ifically in small habitats if no other
species are present.

Any attempts to re-establ ish native fishes should be accompanied by
studies geared toward evaluation and documentation of introduction
successes or failures. Experimental stocKings should be made and studied
to determine interactions of reintroduced natives and resident non-native
species. Some important questions to be answered include the following.
What is the pattern of dispersal and survivorship of young native species
upon stocKing and over a time period after introduction? What is the
relative survivorship of introduced native fishes in the presence and
absence of potential predators and competitors? What species prey on
introduced young of natjve species and what are the predation rates and
overall pressures? And, do competitive interactions such as red shiner and
young of native species feeding on the same ~oods comprise a significant
problem, or is .!ood:-.bunc~ant ~nough for 2111"

Mainstream and Tributaries in the Grand Canyon Reach

Al ~:-:o!...:ghst j 1 ~ flor,'Jing in a natu:=.~ channel, th~ re:-.c:-, of Col()r.o..do
River from La);;e !:J:d..\!e~1 t~r:,ugh Granc Can/on ~htional Park to head',~~.~0;'= .Jf

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