WSP11103

• File Number: 8240.300.10
• Description: San Juan Recovery Implementation Program
• Basin: San Juan/Dolores
• Date: 2/1/1995
• Author: SJRIP
• Title: San Juan River Basin Recovery Implementation Program - Program Document
• Water Supply Pro - Doc Type: Publication

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subsequently they become prey for piscivorous native fishes. In
a few instances, native predatory fish may utilize introduced
forms (e.g., rainbow trout) when native prey are absent or
greatly diminished in abundance.

In the San Juan River sub-basin, 23 non-native fish species have
been reported. In comparison to other Upper Colorado River Basin
drainages, the San Juan has few common or widely distributed non-
native fish species. Of these, only common carp and channel
catfish are common in main channel habitats within warmwater
reaches and red shiner and fathead minnow are the most common
non-natives in associated low-velocity habitats. Other non-
native species in warmwater reaches are uncommon or occur
sporadically. In main channel habitats, native fish species
remain numerically dominant, but non-natives numerically dominate
many low-velocity habitats.

Although the impact of non-native fishes upon the native fish
fauna has been known for some time, and means to eliminate or
reduce problem species are limited, expensive, and usually not
feasible,the potential to conduct such actions in this
Implementation Program will be evaluated. An essential element
of any control effort is accurate definition of the problem.
Among non-native fishes inhabiting the San Juan, the mode of
interaction of particular non-native species with specific native
species (or life stages of each) is not clearly defined. For
example, adults of channel catfish consume a variety of food
items, including fish. However, the relative impact of their
foraging habits upon particular life stages of Colorado squawfish
or other natives is not known. In low-velocity habitats, young
of Colorado squawfish may compete for food and habitat with
several non-natives. The effect of this presumed competition
upon recruitment of young of Colorado squawfish to larger size-
classes is unknown.

Although the San Juan River drainage is occupied by several
warmwater non-native fish species, additional stocking of these
species or introduction of new species will only exacerbate
problems. In this sense, the best control is prevention of
potential problems by eliminating stocking of non-native
warmwater species.

The high flows of 1987 demonstrated an effective method of
control of non-native species. That year, successful
reproduction by channel catfish was markedly lower than in
subsequent years when spring run-off was much lower and of
shorter duration.

Other controls, such as chemical treatment, are biologically and
logistically infeasible in almost all situations on the San Juan
River. Some actions, while not strictly control, may be
warranted in particular instances. Such actions might include