WSP07867

• File Number: 8240.300.31.J
• Description: San Juan River - Environmental Studies
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 2/1/2000
• Title: Ichthyofaunal Surveys of Tributaries of the San Juan River - NM
• Water Supply Pro - Doc Type: Report/Study

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CONCLUSIONS

The following are general conclusions that are supported by fish surveys on tributaries of
the San Juan River:
. Most fish surveys have occurred since 1970,
. In most reaches of San Juan River tributaries native fish are still the dominant
speCies,
. Populations of roundail chub in the Animas River may have substantially declined
following the introduction of non-native fish species,
. Self-sustaining populations of non-native fish species currently exist in all major
tributaries of the San Juan River.
. The white sucker is established in the Animas River, but has not yet been reported
from the La Plata River.

Historical studies of fish in tributaries of the San Juan River provide an account of native
and non-native species composition during a period of non-native introduction. The
Animas River has been the site of more historical fish surveys and earlier sampling
events than other tributaries, The earliest recorded sampling events (and other
unconfirmed early reports) in the Animas River included only records of native fish
species, By the I 950s, non-native fish had been detected in a reach of the Animas River
upstream ofthe Colorado border. Non-native species have persisted in the Animas River
since they were first reported; however, the composition and number of species have
changed.

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Because there are few records of fish surveys in other tributaries prior to 1970, it is likely
that some non-native fish were already established in various tributaries before they were
reported, However, one of the earliest surveys from the La Plata River (1966) only
provided evidence of the existence of native fish. Although some non-native species had
been stocked in the La Plata River prior to this time, most non-native species were
probably not established over a widespread area,

The expansion of non-native fish in tributaries of the upper San Juan River has been
concurrent with a decline in certain native fish species. There have been several
historical reports that suggest that native fish may have been relatively abundant in areas
where recent surveys indicated they were rare or nonexistent (Jordan 1891, Koster 1957,
Dean 1961, Olson 1962a). Several researchers have also conunented on the decline of
certain native speCies (Sublette 1977, Platania and Bestgen 1988, Platania and Young
1990). In fact, the data presented here suggests that roundtail chubs may have been
common in some reaches of the Animas River, A review of historical fish surveys
suggests that the establishment of species (and species composition) is a dynamic
process. Future surveys will be necessary answer more questions regarding the balance
of native and non-native fish fauna in tributaries ofthe upper San Juan River.

Draft Final Tributary Report
Miller Ecological Consultants, Inc.

January 31, 2000
Page 26