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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instead wait for appropriate spawning temperatures to initiate migration into these areas.
The water temperatures and the presence of large numbers of adults congregating in the
backwaters in early April suggest that the primary spawning period in the Yampa River
occurs during this period. We continued to collect sexually mature northern pike
throughout May, which was similar to the findings of Nesler (1995). These results
suggest that the entire spawning period may last for about a month, as has been reported
elsewhere (Farrell 2001; Miller et al. 2001). The presence of more males than females
during the primary spawning period is consistent with other studies of northern pike
spawning activity (Billard 1996).
The dynamic nature of lotic systems makes identifying spawning habitats
challenging. For example, spawning habitat that may look suitable during April may be
negatively affected by the spring runoff in May and areas that look good during May
might not have water during the early April spawning period. From year to year the
quality of nursery habitat can change because of different spring runoff levels. Initial
counts of backwater habitats in the river indicated that they were widespread, but closer
observation revealed that good spawning and nursery habitat is limited. Backwater
orientation to the river was a major indicator of whether the backwater would be
protected or not from spring runoff flows and thus serves as good nursery habitat.
Backwaters that are parallel to the main river channel have the possibility of experiencing
direct flow through the backwater if it connects to the main channel during spring runoff,
thus lowering the value of these areas as nursery habitat. In contrast, backwaters that are
more or less perpendicular to the main channel are less likely to receive direct flow
through them during spring runoff. Large backwaters of this type were relatively
uncommon in our study area.

The amount of spawning habitat available does not seem to differ greatly from
year to year, regardless of the magnitude of spring runoff, but spring runoff could
seriously impact the recruitment of age-O northern pike during the nursery period. Our
analysis of backwaters indicated that a large majority showed signs of being connected to
the main channel during a typical spring runoff. During a runoff of large magnitude,
similar to 2003, we observed that most backwater nursery habitats became part of the
main channel or at least experience increased flows. During a spring runoff of low
magnitude, as in 2002, backwater nursery habitat is less likely to connect to the main
channel, but has the added threat of being dewatered. On these occasions some age-O
pike are able to find suitable nursery habitat in low velocity areas of the main channel,
which can serve as de facto backwater habitat. While the spring runoff appears to create
abundant backwater nursery habitat, these habitats may in fact be unsuitable for age-O
pike because of flushing flows.

Based on our observations, the primary spawning period on the Yampa River is
from April 1-15. Egg incubation may last between 12 and 17 days at water temperatures
between 7.80 and 100 C (Swift 1965) at which point larvae attach to vegetation for 5-12
days (Billard 1996) after which they become free-swimming (Figure 6). Based on this
age-O northern pike timeline for development, we suspect that spring runoff flows in May
and June could be detrimental to age-O northern pike recruitment. Most backwaters
available for spawning and nursery habitat experience strong currents during spring flows

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