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Last modified
7/14/2009 5:02:35 PM
Creation date
5/22/2009 5:19:10 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
9463
Author
Badame, P. V. and J. M. Hudson.
Title
Reintroduction and Monitoring of Hatchery-reared Bonytail in the Colorado and Green Rivers; 1996-2001.
USFW Year
2001.
USFW - Doc Type
03-13,
Copyright Material
NO
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<br />, <br /> <br />long smaller bonytail (< 150 mm) have been in the river. A final electrofishing trip in August <br />yielded four bonytail with a mean TL of 124.0 mm (Table 6). <br /> <br />2002 - During the second year ofCPM estimates on the Green River, 12 bonytail were captured. <br />These fish ranged in size from 140 to 351 mm. One additional CWT bonytail (TL=370 mm) was <br />captured in Gray Canyon at RM 148 on June 21, the presence of the CWT indicates that the fish <br />was from a 1998-2000 cohort. The specific cohort of origin could not be determined for any of <br />the 2002 recaptures. <br /> <br />Recaptures by size class <br /> <br />Regressions of the mean TL of a cohort at release and the electrofishing RCR for that cohort, <br />within six months of stocking, were examined for the Colorado and Green rivers. Separate <br />regressions were made for the Colorado and Green due to significant differences in RCR. To <br />utilize all available data, the cohort of origin was estimated based on TL at the time of stocking <br />for recaptures occurring after the spring of 1999. A positive relationship (R2 = 0.85, Figure 7) <br />was observed on the Colorado, while no relationship (R2 = 0.08, Figure 7) was found on the <br />Green River. The strength of the relationship found on the Colorado is based on the high RCR <br />values from one small stocking of large fish (mean TL=316.2 mm) in 1998. When this cohort is <br />removed from analysis, no relationship (R2 = 0.01) is observed. The obvious problem with these <br />regressions is a lack of fish stocked at sizes greater than 160 mm. <br /> <br />Further evidence of this dilemma is seen by looking at the length frequencies of stocked and <br />recaptured fish between 1996 and 1998, when all fish were individually marked and measured <br />before release (Figure 2). During this time period, 46.5% of the bonytail stocked were 80-120 <br />mm, 50.8% were 120-160 mm, 1. I % were 160-200 mm, and 1.6% were over 260 mm (Figure <br />2). For individuals recaptured from these cohorts, the TL at the time of stocking was distributed <br />as follows: 57.4% were 80-120 mm, 36.1% were 120-160 mm, 1.6% were 160-200 mm, and <br />4.9<<>>10 were 300-340 mm (Figure 2). The increase in return rate observed for the cohort oflarge <br />bonytail released in 1998 was consistent with the results reported during razorback monitoring in <br />the upper Colorado and Gunnison rivers (Burdick 2002). Unfortunately, this was the only cohort <br />of fish over 300 mm released. <br /> <br />In 2000, both the Colorado and Green rivers received a large release ofbonytail with mean total <br />lengths greater than 160 mm (19,000 and 9,962, respectively; Table 2). The largest number of <br />long-term recaptures for both rivers occurred the following year in 2001 (Table 4). However, <br />because multiple cohorts were released in 2000 it was not possible to attribute the long-term <br />recaptures to a specific cohort of origin. Overall, the lack of fish stocked at larger sizes and the <br />switch to coded wire tags greatly reduced the ability to assess any relationship between size and <br />survivability . <br /> <br />12 <br />
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