9449

• UCREFRP Catalog Number: 9449
• Author: Hawkins, J. A.
• Title: Recapture and growth rates of three Colorado River endangered fish species
• USFW Year: 2003.
• USFW - Doc Type: a comparison between electrofishing and non-electrofishing.
• Copyright Material: NO

capture were not analyzed by ANCOVA because most fish comprised two distinct size
groups with little overlap in length (Figure 3). To adjust for size differences, mean
growth rate was calculated separately for small fish (x400-mm total length) and large
fish (>400-mm total length) and mean growth rates of razorback sucker in each length
group were similar and not significantly different (Table 3). Growth rates of razorback
sucker captured in the second growing season overall were low and similar between
gear types (Tables 3, 5 and 7; Figure 3).
DISCUSSION
If a sampling gear caused higher mortality compared to another gear, then the
expectation would be lower recapture rates of fish captured by the former gear due to
the increased mortality. For all three species, recapture rates of fish initially captured
by electrofishing were similar to rates of fish captured by non-electrofishing gears and
did not suggest substantially higher mortality due to gear type. Although the recapture
rate of Colorado pikeminnow initially captured with electrofishing was lower and
statistically different (P=0.04) than the recapture rate of Colorado pikeminnow captured
by non-electrofishing gears, the difference was small (2.4%) and statistical significance
was likely due to the extremely large sample size providing high statistical power to
detect small differences. The biological significance of this small difference is likely
minimal. In contrast, razorback sucker initially caught by electrofishing were recaptured
at a higher rate than those caught by non-electrofishing gears; however, the difference
was also relatively small (2.7%) and not statistically different.
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