. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. STURGEON SPAWNING 39. I I I I I I I I I I I I I I I 16 18 20 22 « 26 28 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 I 3 5 / 9 II 13 15 17 19 21 23 25 2f 29 I 5 5 1 9 II 13 15 If 19 21 23 25 21 29 FEBRUARY | MARCH | APRIL | MAY FIGURE 7. Sturgeon spawning periodicity in the Sacramento River in 1973, estimated from larval ages interpolated from Figure 6. Berg 1962; Geibel 1966; Mag^nin 1966). Such conditions mainly occur upstream from Colu
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. STURGEON SPAWNING 39. I I I I I I I I I I I I I I I 16 18 20 22 « 26 28 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 I 3 5 / 9 II 13 15 17 19 21 23 25 2f 29 I 5 5 1 9 II 13 15 If 19 21 23 25 21 29 FEBRUARY | MARCH | APRIL | MAY FIGURE 7. Sturgeon spawning periodicity in the Sacramento River in 1973, estimated from larval ages interpolated from Figure 6. Berg 1962; Geibel 1966; Mag^nin 1966). Such conditions mainly occur upstream from Colusa in the Sacramento River. Below Colusa the river has a mud and sand bottom and moderate current. Since the spawning area apparently did not extend far above Colusa in 1973, my study dis- agrees with published descriptions. Sturgeon probably spawn farther upstream in the Sacramento River than my study suggests. Between Jime 17 and July 10, 1974, 12 youug sturgeon about 25-60 mm ( inches) were collected at the intake of the Glenn-Colusa Canal near Hamilton City (rkm 330 [rm 205]) (Jerry AVise and. Ronald Decoto, Calif. Fish and Game, pers. commun.). Therefore, either sturgeon spawned farther upstream in 1974 than in 1973, or the 1973 survey techniques were inefficient for catching larvae in that section of the river. The sturgeon nursery is apparently formed by both the river near and below the spawning area and the Delta and bays do-wnstream. Many lar^'ae are flushed to the Delta and Suisun Bay in years with high runoff, but they are scarce there in years with low runoff (Stevens and Miller 1970). Hence, immigration age to these areas must vary with spring river flow. Spring 1974 flows were high, so the collection of juveniles near Hamilton City that summer and the scarcity of larvae in the Delta, when flows are low suggests the river is an important nursery in all years. Although I did not catch sturgeon older than about 16 days, my stationary nets probably did not f
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