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

Species' General Response to Proposed Action - Bonytail Chub
and Razorback Sucker

This discussion looks, in a general way, at the types of changes that have occurred in the LCR and
what the effects to the historic habitats were. It is intended to be an introduction to the types of
effects that have impacted these species in the past, and it is neither detailed nor does it specificall y
analyze the action under consultation.

Historically, the Colorado River and its tributaries possessed a remarkable degree of variance of
physical conditions which created fish habitats. Extremes in flows of both seasonally and yearly
cycles, water quality, velocity of flows, distribution of types of habitats and geographic factors of
distance and elevation were the defining features of the river. The native fish species, including
the bony tail chub and razorback sucker, had evolved in and with that variance and had strategies
to maintain their place in the system. Both species live to 45-50 years of age and maintain
fecunditY and fertility well into old age. A long-lived and fertile species can ride out periods of
too much or too little water in the system to allow for successful recruitment to the population. Th e
age structure of the population might change, but even that might be within the normal pattern of
the species. Adults also avoid areas of highest velocity waters and take refuge in flooded areas,
lessening risk of injury, death or removal from the local population during the danger period.
Avoiding seasonal low water or drought-related mortality was more difficult, but the fecundity of
the survivors would enable a short time to recovery of population size. In the event of local
extirpation of a population, the interconnected tributaries provided access throughout the basin for
migrants.

The LCR now has experienced actions that have changed the historical patterns of variance and
have greatly altered the system as a whole. A general chronology of these actions within the action
area and their effects can be found in the section of this BO describing the environmental baseline.
Specific areas have been more or less affected, some completely changed, others only somewhat
changed. In only a very few places have the bony tail chub and razorback sucker persisted.

River shores and floodplains are often developed for agriculture, recreational activities, residential
and other urban/suburban facilities. Such development results in losses to riparian, marsh and
backwater habitats in the floodplain. Placement of levees and bank stabilization struc tures to keep
the river from flooding out these developments is an associated impact. Destabilized shores may
be altered by placement of beaches, boat launch facilities, docks, and construction right at waters I
edge. Losses of habitats within the floodplains and along shorelines can be sign ificant and further
compound problems associated with native fish habitat.

The placement of dams, large or small, inundates riverine habitats and creates reservoirs or ponded
areas and blocks migration upstream from the location. Depending on the type and size of the
dam, downstream movements are also affected. Creation of reservoirs and ponded areas drowns

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