9299

• UCREFRP Catalog Number: 9299
• Author: Anderson, R. and J. Mumma.
• Title: Aspinall Studies
• USFW Year: 1999.
• USFW - Doc Type: Annual assessment of Colorado Pikeminnow Larval Production in the Gunnison and Colorado Rivers, Colorado 1992-1996.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

two high flow years (1993 and 1995) summer (post-runoff) densities were less than in the
spring, presumably because the runoff flooded preferred NNC habitats (backwaters) which
reduced habitat availability during high flows. In the other three years (1992, 1994 and
1996) NNC density increased in the summer indicating peak flows of those years did not
negatively impact habitat availability and/or temperatures suitable for reproduction were
reached sooner. The reduced NNC density in 1993 and 1995 is therefore attributed to
runoff conditions. The high spring NNC density in 1995 after the low year of 1994
indicates there can be a large range in variability between years.

Table 7. Average ofNNC densities (number/100m3 seined) from the
upper (near Moab) and lower (below Potash mine) stations on
Colorado River (Trammel and Chart 1999a).

MER
m3
NNC
943
1075
1866
4065
3570
2304
1009
2965
3507

Non Native Cyprinid-Backwater Density. Colorado (ISMP)

.

Backwaters in Colorado are sampled every year during the fall using the ISMP
methodology (McAda, 1998). ISMP Reach 2 is 30 miles of the Colorado River from the
confluence of the Colorado and Gunnison Rivers downstream to RM 139 (Mee Canyon).
The Reach 2 NNC backwater density was highly correlated with drift density measured at
Loma, Colorado (R2 == 0.776) (Table 8). The relationship between NNC drift abundance
and density in backwaters was positive with 1992 the highest and 1996 the lowest for both
larval drift and backwater abundance.

Fall NNC densities in backwaters in Reach 2 were higher in the two low flow years
than in the two high flow years, but the intermediate flow year (1996) had the lowest
density of the period. Fall NNC density in Reach 2 was not strongly correlated with
Reach 1, located between River Mile 0 to 110 (Table 8). The coefficient of determination
for NNC densities between Reach 1 and 2 was only 0.042.

17