. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. STURGEON SPAWNING 35 25 20 15- COLUSA. 1 10- 5 - I I RIVER KILOMETER .X. ABOVE THE MOUTH OF THE FEATHER RIVER I I M I I I I I I I II I I I I I I I I IIIN I I I I I I I I I I I I I I I I I I I I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I n I 11 I I I I I I I I M I M I I I I I I I I 5 10 15 20 25 31 5 10 15 20 25 30 5 10 15 20 25 51 5 10 15 20 MARCH I APRIL I MAY I JUNE FIGURE 2. Temporal distribution of larva
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. STURGEON SPAWNING 35 25 20 15- COLUSA. 1 10- 5 - I I RIVER KILOMETER .X. ABOVE THE MOUTH OF THE FEATHER RIVER I I M I I I I I I I II I I I I I I I I IIIN I I I I I I I I I I I I I I I I I I I I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I n I 11 I I I I I I I I M I M I I I I I I I I 5 10 15 20 25 31 5 10 15 20 25 30 5 10 15 20 25 51 5 10 15 20 MARCH I APRIL I MAY I JUNE FIGURE 2. Temporal distribution of larval sturgeon caught during the sturgeon spawning survey in the Sacramento River in 1973. Size Mean length of the 206 sturgeon larvae measured was mm ( inch). One larvae was mm ( inch) long; the rest were between and mm ( inch). Length frequency distributions were about the same for the three stations and differences in mean lengths be- tween stations were not significant (F = , P = ) (Figure 3). Length frequencies in different months were basically similar, but mean size increased slightly each month (F'= , P < ) (Figure 4), possibly reflecting a direct relationship between growth rate and water temperature. Spawning Time, Temperature, and River Flow Larval catches did not provide a direct measure of spawning time due to variable time lags between spawning and capture. To estimate spawn- ing time, I assumed Sacramento River sturgeon developed at rates re- ported for European and Asiatic species (Cherfas 1956; Nikolskii 1961; Geibel 1966). These rates depend on temperature and are known for the incubation period and for the interval from hatching to active feeding. Only three of the 206 larvae I measured were shorter than 8 mm ( inch) (Figure 4), so I assumed that was the approximate length at hatching. Larvae longer than 18 mm ( inch) had well- developed mouthparts, had absorbed their yolk sacs, and had probably begun to fe
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