Stamp Falls fishway counts, adipose clip/CWT recovery and biological sampling of chinook salmon escapements in Stamp River and Robertson Creek Hatchery, 1993 / by T.C. Nelson for Department of Fisheries...: Fs97-4/2255E-PDF

"Estimates of salmon escapement were derived for the Stamp River for 1993 using visual counts at the Stamp Falls Fishway. After adjusting for observer error, the total escapement of adult chinook salmon (Oncorhynchus tshawytscha) to the Stamp River was estimated at 96,254 ± 4707; the total escapement of jack chinook was estimated at 1806 (confidence limits are not presented due to the low number of observations of jack chinook during verification tests). Escapement estimates for adult and jack coho salmon are also presented, as well as partial estimates for sockeye. This study is part of the Chinook Key Stream Program. The age, size, sex, and hatchery contributions for chinook salmon in the upper Stamp River are also described using data from carcass recovery operations and live returns to Robertson Creek Hatchery. The dominant male age groups for the in-river chinook population were age 4 and age 3, respectively, and the dominant male age groups for the hatchery chinook population were age 3 and age 4, respectively. The dominant female age groups for both the in-river and hatchery populations were age 4 and age 5, respectively. For both the in-river and hatchery populations, the mean lengths of all age groups of female chinook were larger than the corresponding mean lengths of males. Escapement of adipose-clipped chinook to the entire Stamp River system (hatchery plus upper river returns) was 3,126 and represented 3.4% of the entire population. This estimate was further stratified by age, sex, and tag code. The total hatchery contribution (marked and unmarked) to the escapement was estimated by expanding the number of observed adipose clips by the adipose-clip mark rate at release. In 1993, Robertson Creek Hatchery contributed 82.0% of the total chinook escapement to the Stamp River. This hatchery contribution estimate was compared with a contribution estimate calculated using the Mark Recovery Program (MRP) method of coded wire tag expansions (Kuhn et al. 1988). Using the MRP method, the total contribution of Robertson Creek Hatchery to the 1993 chinook escapement was 74.7%. Reasons for the differences between hatchery contribution estimates using the two methods are discussed"--Abstract, page viii.

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