9314

• UCREFRP Catalog Number: 9314
• Author: Wick, E. J. and J. A. Hawkins.
• Title: Colorado Squawfish Winter Habitat Study.
• USFW Year: 1989.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

temporal, or behavioral integrity from other randomly breeding groups of
that same species (Kutkuhn 1981). This stock definition applies to multiple
stocks within an individual river or a single stock comprising fish from
various rivers within a basin (Philipp et al. 1993). The biological
uniqueness resulting from isolation or geographic separation is an
evolutionary one and such stocks have been referred to as "evolutionary
significant units" (Dizon et al. 1992).
Criteria considered to identify and characterize fish stocks include:
distribution and abundance, spawning, migration, and genetic information
Dizon et al. 1992, Ihssen et al. 1981). Spawning behavior and physiology
may be important to survival in a particular environment (Larkin 1981). The
criteria used to identify and characterize endangered and candidate fish
stocks will be:
Geographic Distribution and Abundance. The basic criterion used to
separate fish stocks are distribution and abundance of each species.
Some disjunct stocks are geographically separated from others and do not
appear to exhibit interchange between them. For example, the humpback
chub is found as relatively small concentrations of fish that are widely
separated and confined to short reaches of deep canyon areas (Valdez and
Clemmer 1982; Tyus and Karp 1989: Tyus and Karp 1991).
2. Identified or Suspected Spawning Sites. Spawning sites and time of
spawning must be determined. This will be accomplished by collecting
ripe fish in specific river reaches, and, for some species, collecting
of larval fishes downstream from documented or suspected spawning sites.
In the Upper Colorado River Basin all major tributaries have been
sampled to determine the distribution and abundance of endemic and
introduced fishes (Bestgen 1990; McAda et al. 1993: Miller et al. 1982:
U.S. Fish and Wildlife Service 1990a, 1990b, 1991). Additional work of
this type needs to be done in the other major river systems in Region 6.
3. Migration. Movement and Interchange between Stocks. Some endangered and
candidate fishes are known to migrate to specific spawning areas but
return to a home area during the remainder of the year. The Colorado
squawfish migrates long distances to spawning sites and is considered
the most mobile of the endangered Colorado River fishes (Tyus 1991).
The razorback sucker exhibits moderate migrational movements (Tyus and
Karp 1991). Some humpback chub stocks (e.g., the stocks in Black Rocks
and Westwater Canyons in the Colorado River) do not migrate for spawning
(Kaeding et al. 1990) but a lower basin humpback chub stock spawns in
the Little Colorado River and uses the mainstem Colorado River in the
Grand Canyon during the remainder of the year (Kaeding and Zimmerman
1983). The greenback cutthroat trout returns to a specific spawning
site.
Dams have fragmented habitat preventing free movement of fishes.
Therefore, some of the geographic separation among stocks is due to
altered habitats. In most cases, fish are known to move between
different river reaches during the spawning season. A small amount of
interchange among stocks is a natural phenomenon that provides for