9509

• UCREFRP Catalog Number: 9509
• Author: Hill, C. G.
• Title: Dynamics of Northern Pike Spawning and Nursery Habitat in the Yampa River, Colorado.
• USFW Year: 2004.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

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backwater spawmng habitats during the period when we observed northern pike
spawning. During 2003, water temperatures in the Yampa River near Hayden did not
reach 4.40 C until late March and did not consistently reach 7.80 C until early April.

An examination ofthe 1999 aerial photographs of the river indicated the existence
of more than 100 potential backwaters between Steamboat Springs and Craig. During
our on-the-ground investigations between Steamboat Springs and Craig, only 52 possible
spawning backwaters were identified. Some presumed backwaters in the 1999 photos
probably no longer existed, were active side channels or dry, or were misidentified from
irrigation ditches. During sampling for age-O pike in 2002 and 2003, backwaters smaller
than 557 m2 had few fish and never more than 10 age-O pike on a single sampling
occasion. Therefore, backwaters that were smaller than this size were deemed
unproductive sites for northern pike recruitment. Nineteen of the 52 sites were smaller
than 557 m2 and would be expected to contribute very few age-O pike. Of the remaining
33 larger sites, 8 showed signs of flushing flow effects from spring runoff, 13 showed
some signs of flow effects, and 12 showed no signs of flushing flow impacts (Figure 4).
The 12 backwaters larger than 557 m2 that showed no signs of flushing flow impacts
from spring runoff and the 5 backwaters larger than 557 m2 that showed some signs of
flow effects and were "perpendicular" to the main channel with only one point of
connection to riverine flows were considered to be the best backwater spawning habitats
available.

Regressions of depth vs. flow were based on 9 to 14 data points depending on the
site, which resulted in r2 values between 0.94 and 0.99. Analysis of contour maps and
depth vs. flow information for each study site revealed that wetted area showed only a
small change between 2002 and 2003 during early April (April 1-15) even though the
spring runoff was dramatically different in the two years (Table 1). The site at river mile
155 was the only site that showed a dramatic change in wetted area, but this site had a
low floodplain separating the backwater from the river, which allowed for a large change
in area from a small change in water depth. Contour maps for this site during the peak
spring flow of 2002 and 2003 showed that this was the only site connected to the main
channel during both years. Two sites showed possible connection and the rest did not
show connection to the main channel during the peak spring runoff of 2002. During the
higher peak spring runoff in 2003 one site showed no connection, one site showed
possible connection and the rest were connected to the main channel during the spring
runoff.

Age-O northern pike were sampled at 11 sites during 2002 and 12 sites during
2003. The first sampling period was June 25-28, 2002 and June 24-27, 2003. The
second sampling period was July 10-11, 2002 and June 30-July 2, 2003. The third
sampling period was July 20-23, 2003. Five sites were dewatered before sampling began
in 2002, but age-O northern pike were found in the river adjacent to one dry site. Also
during 2002, most backwaters were dry by the end of July so the third period samples
were not collected. During 2003, one site was not sampled and one site dewatered during
the second sampling period and two additional sites dewatered before the third sampling
period. The CPUE information in 2002 shows a wide range in CPUE for backwater

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