8031

• UCREFRP Catalog Number: 8031
• Author: U.S. Department of the Interior.
• Title: Fish and Wildlife Service Final Biological and Conference Opinion on Lower Colorado River Operations and Maintenance - Lake Mead to Southerly International Boundary.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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BIOLOGICAL OPINION

Status of the Species

Habitat needs of larval razorback suckers are not well known. Warm, shallow water appears to
be important. Shallow shorelines, backwaters, inundated bottomlands and similar areas have been
identified (Sigler and Miller 1963, Marsh and Minckley 1989, Tyus and Karp 1989, 1990,
Minckley et al. 1991). For the first period of life, larval razorbacks are nocturnal and hide du ring
the day. Diet during this period is mostly plankton (Marsh and Langhorst 1988, Papoulias 1988).
Young fish grow fairly quickly with growth slowing once adult size is reached (McCarthy and
Minckley 1987). Little is known of juvenile habitat preferences.

Population Dynamics

The razorback sucker is adapted to the widely fluctuating physical environment of the historical
Colorado River. Adults cari live 45-50 years and, once reaching maturity between two and seven
years of age (Minckley 1983), apparently produce viable gametes even when quite old. The ability
of razorback suckers to spawn in a variety of habitats, flows and over a long season are also
survival adaptations. In the event of several consecutive years with little or no recruitment (due
to either too much or too little water), the demographics of the population as a whole might shift,
but future reproduction would not be compromised. Average fecundity recorded in studies ranged
from 100,800 to 46,740 eggs per female (Bestgen 1990). With a varying age of maturity and the
fecundity of the species, it would be possible to quickly repopulate after a catastrophic loss of
adults.

Rangewide Present Status

The razorback sucker was listed as an endangered species due to declining or extirpated
populations throughout the range of the species. The causes of these declines are changes to
biological and physical features of the habitat. The effects of these changes have been most clearl y
noted by the almost complete lack of natural recruitment to any population in the historic range of
the species. Populations are generally small and composed of aging individuals. A recovery plan
is being drafted for this species. Recovery efforts under the Recovery Implementation Program
in the Upper Basin have begun, but significant recovery results have not been achieved for this
species. In the Lower Basin, efforts to reintroduce the species in the Gila, Salt and Verde rivers
have not been successful in establishing self-sustaining populations. Reintroduction efforts are
currently ongoing only in the Verde River. Augmentation efforts along the LCR propose to
replace the aging populations in Lakes Havasu and Mohave with young fish from protected-rearing
site programs. This may prevent the imminent extinction of the species in the wild, but appears
less capable of ensuring long term survival or recovery. Overall, the status of the razorback sucke r
in the wild continues to decline.

Bony tail chub and razorback suckers were key components of the sparse fish fauna that historically
occupied the LCR. Spawning and nursery areas were provided largely during spring floods that
provided space, food and protection during early life stages of both species. Initiation of spawning

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