WSP01460

• File Number: 8240.300.02
• Description: San Juan River Recovery Implementation Program - Recovery Plans & Information
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 9/1/2000
• Author: Paul Holden - Bio/We
• Title: San Juan River Recovery Implementation Program Biology Committee - Program Evaluation Report - for the 7-Year Research Period 1991-1997
• Water Supply Pro - Doc Type: Report/Study

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and juveniles were found in secondary channel-associated backwaters and low-velocity habitats (Propst
and Hobbes 2000, Trammell and Archer 2000). Secondary channels are also common in portions of the
river with high habitat richness, such as the Mixer, another indication of their importance to the native fish
community.

Late summer and autumn studies of secondary channels were generally comparable with studies of
backwaters in the Green and Colorado rivers, and the studies by Gido and Propst (1999) provided data
that showed how the small fish portion of the San Juan River fish community varied with flow and other
factors, such as late summer storm events. These studies helped to show that, even if the main channel San
Juan River was dominated by run and riffle habitats, a considerable amount ofIow-velocity habitat existed
for smaIl fish in secondary channels.

The question of whether a rare, key habitat type is limiting remains unanswered. For the present low
population levels of both endangered species in the San Juan River, there does not appear to be a shortage
of key habitats. The YOY Colorado pikeminnow stocking study (Tranunell and Archer 2000) showed
that habitat for this age class was common, as shown by the large portion of river where the fish were
retained, and sufficient for a high level of retention in the river. Archer and Crowl (2000b) compared the
amount of nursery (backwater) habitat available in the San Juan River with that available in the Green and
Colorado rivers using similar sampling techniques (Table 3.4). They concluded that the amount of habitat
in Reach 1, near the Lake Powell confluence, was the highest in any reach studied in any of the three rivers,
and that other San Juan Riverreaches had amounts of backwater habitat similar to the Green and Colorado
rivers. Lamarra (1999) compared San Juan River backwaters as a percent of TW A (Figure 3.5) with
similar data from the Colorado River. He concluded that, even in Reach I, backwater habitat was three
times less in the San Juan River. The difference in results is likely because of different habitat definitions
(Archer and Crowl used nursery habitats of which backwaters, under Lamarra's definition, are only a part),
and comparisons of different sections of the various rivers. Although rare, nursery habitats (backwater,
low-velocity, and slackwater) do not appear to be limiting in the San Juan River for the numbers of
Colorado pikeminnow in the river during the 7-year research period.

Table 3.4.

Total area (square meters) of low-velocity habitats per mile in nursery habitat
study sections ofthe San Juan, Green, and Colorado rivers, September 1994
to 1997 (Source: Archer and CrowI2000b). Flows in the San Juan River were
generally 900 to 1,080 cfs during 1994 to 1996 and varied from 3,100 to 5,260
cfs during 1997.

1994
1995
1995
1997

NA
496.6
743.2
464.6

62.0
349.2
568.2
1.282.4

214.2
371.0
807.0
332.8

1861.6
661.6
1.968.0
1028.2

1572.4
359.9
596.8
NA

1.426.3
307.4
1,047.6
NA

September 2000

3-29

Program Evaluation Report