8105

• UCREFRP Catalog Number: 8105
• Author: Haines, G. B., D. W. Beyers and T. Modde.
• Title: Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
• USFW Year: 1998.
• USFW - Doc Type: Recovery Program Project 36,
• Copyright Material: NO

Methods

Capture-Recapture Population Estimates
Fish capture and marking. - The abundance of young- of-year Colorado squawfish in
autumn and the following spring was estimated using capture-recapture population estimation
methods (Otis et al. 1978; Seber 1982; Haines and Modde 1996). Study sites were sampled on
three occasions (passes) for each population estimate. A pass consisted of seining all backwaters
with surface area 2: 3 m2 within each study reach. Seines were 4.5-m long x 1.9-m deep with 4.0-
mm bar mesh. The area seined was generally between 70 and 100% of the of the total surface
area. In the Jensen reach, however, a few backwaters were large and deep and only about 50% of
the total area could be seined. The number of seine hauls per backwater averaged 2-3 for the
Canyonlands reach and ranged from 1 to 6; the backwaters in the Jensen reach were somewhat
larger and the number of seine hauls per backwater averaged 3-5 and ranged from 1 to 23. The
backwaters were not blocked prior to seining. Colorado squawfish were marked on the first two
passes but not on the third, with one exception: in autumn 1992 fish were marked only on the
first pass. Dates of each sampling pass are given in Appendix 1.
Captured Colorado squawfish < 100-mm total length (TL) were anesthetized with 0.1 g/L
MS-222 and marked with syringe-injected elastomer (Northwest Marine Technology, Shaw
Island, Washington). Approximately 100 fish (if available) were selected at random and
measured (TL) during each population estimate. Fish were allowed to recover in a 20-L pail of
river water for 20 to 30 min while seining, marking, and data collection were completed.
Marked fish were released into backwaters where they were captured. On seven occasions
postmarking survival was estimated by retaining marked fish ovemight (18 to 19 h) in a floating
enclosure.

Captur~d Colorado squawfish > 100 mm TL were not considered part of the age-O cohort.
These fish were measured (TL), marked with intemally implanted passive integrated transponder
(PIT) tags (Prentice et al. 1990) and released back into the same backwater.
Parameter estimates. - Population estimates were calculated using the computer
program CAPTURE (White et al. 1982) assuming closed capture-recapture models (Otis et al.

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