. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 178 CALIFORNIA FISH AND CAME mouth) on February 17, 1977. This location is above Robles Diversion Dam, completed in 1959, which prevents upstream migration of fish under most flow conditions. Otoliths were removed, stored in 100% glycerin, and measured using an ocular microscope (see McKern, Norton, and Koski 1974 and Rybock et al. 1975 for details of the procedure). Despite clearing in glycerin, 20% (11 /54) of the otoliths were unre
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 178 CALIFORNIA FISH AND CAME mouth) on February 17, 1977. This location is above Robles Diversion Dam, completed in 1959, which prevents upstream migration of fish under most flow conditions. Otoliths were removed, stored in 100% glycerin, and measured using an ocular microscope (see McKern, Norton, and Koski 1974 and Rybock et al. 1975 for details of the procedure). Despite clearing in glycerin, 20% (11 /54) of the otoliths were unreadable. All but two fish, however, had at least one readable otolith. ON measurements recorded for the Ventura River trout were within resident and steelhead trout ON width and length ranges reported from other Pacific coastal streams (McKern et al. 1974, Rybock et al. 1975). Only ON widths were consistently distinct enough to accurately measure in all readable otoliths. The comparison of ON widths showed distinct distributions for unmarked trout taken from above Robles Diversion Dam and marked steelhead trout taken from the middle Ventura River (Figures la and 1c). The ON width distribution for unmarked trout taken from the middle Ventura River, however, spanned nearly the entire range of both marked and unmarked trout (Figure 16). Differ- ences in the mean ON widths of the three groups were analyzed by the "t" test for small samples (Alder and Roessler 1968). The differences between the 0) E 3 5 4 h 3 2 0 0 5 r 4 3 2 I h 5 r 4 3 2 I h .225 n = 7 w= ± (A) n = 10 w= ± (B). n = 8 w= + (C) J 258 .290 .322 .354 .386 .419 .451 Otolith Nuclei ( mm ) Figure 1. Frequency distributions and means (±1 ) of ON widths (millimeters) representing: (A) unmarked rainbow trout above Robles Diversion Dam, Ventura River, (B) un- marked rainbow trout from below Robles Diversion Dam, and (C) marked steelhead rainbow trout from below Robles Dive
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