9694

• UCREFRP Catalog Number: 9694
• Author: Hawkins, J., C. Walford, and A. Hill
• Title: Smallmouth bass control in the middle Yampa River, 2003-2007.
• USFW Year: 2009
• USFW - Doc Type: Contribution 154 Larval Fish Laboratory, Colorado State University.
• Copyright Material: NO

downstream directions and distance between release site and final capture site
increased with time. Emigration was observed from both study sites, but the detection
probability of marked fish was lower in reaches outside of our two study sites because
smallmouth bass were not consistently netted in those reaches, especially during the
first three years. We did not observe tag loss during the short (11-19 days) mark-
recapture period based on double tagging of fish in 2007. This suggests that Floy tags
were adequate for mark-recapture methods used to estimate abundance. Mortality of
fish to anglers was also not a concern during the short time interval of mark-recapture
sampling because environmental conditions (high, cold, turbid flow) were unsuitable for
fishing and we never observed fishermen during that time. Tagging mortality was not
studied, although there were no apparent deaths attributed to tagging during 12 hour
holding periods before translocation. Long-term tag loss is a well documented problem
for smallmouth bass in streams (Walsh and Winkelman 2002). However, we observed
minimal tag loss (40 fish) during the study period, but we probably underestimated long-
term tag loss because it was based on observations such as injury or scar tissue at the
tag site. A more reliable evaluation will require a durable second mark.

Although we documented escapement from Elkhead Reservoir using Floy-tagged fish,
the number of fish that escaped could be biased low if fish are losing tags or if anglers
at the reservoir are intentionally removing tags. If more refined estimates of
escapement are needed then a tamper resistant tag (e.g. PIT tag) is required to prevent
angler removal that could confound results. Because those types of tags typically
require additional handling time and could reduce the time that field crews spend doing
fish removal, we recommend a reassessment of our tagging objectives to determine
whether current tags are suitable. To reduce the potential for unintentional removal of
tags we suggest signs at reservoirs to encourage anglers not to remove tags and to
explain the benefits that tagged fish provide for reservoir management.

We observed biological and environmental differences between Little Yampa Canyon
and Lily Park that may provide insight into the interactions and population dynamics of

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