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

actually captured the fish. Seine captures were excluded because seines targeted
smaller fish that were not equally susceptible to electrofishing.
Rate of recapture was defined as the proportion of fish initially captured by either
electrofishing or non-electrofishing gears that were recaptured at least once. Based on
the assumption that potential acute mortality attributable to the sampling gear would
occur within 30 days post capture, only fish recaptured after 30 days were included in
the analysis. Achi-square test was used to detect statistical differences in recapture
rates. Biological significance was based on the magnitude of differences in rates of
recapture.
Growth was measured for the interval between initial capture and first recapture
and growth rate was calculated for each fish by the equation:
(length at recapture -length at initial capture) / (recapture interval / 30).
Length was measured as total length (mm). Recapture interval was a count of days
from initial capture to recapture but only included days between 1 April and
30 September when mast growth typically occurs (Hawkins 1992). Each growth season
consisted of this 6-months period. Any part of the interval that a fish spent outside of
the growth season (1 October to 31 March) was not counted in the recapture interval to
reduce the influence of non-growth periods on growth rate. Growth rate was
standardized as a monthly (30 days) interva! and was examined separately for the first
and second growing seasons after initial capture. The first season included recaptures
1-5 months (31-182 days) after initial capture and the second season included
4