Oncorhynchus tshawytscha

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General Information
Common Name: 
Central Valley late fall Chinook salmon
FID: 
SOT07
Status: 

Conservation Status in California: Class 2, Vulnerable (Moyle et al. 2011).
The relatively small population size and limited area for spawning and rearing make the single population exceptionally vulnerable to changes in water quality and flow in the Sacramento River.

Life History: 

Life History: The basic life history of Central Valley (CV) late-fall Chinook is similar to that of other Chinook salmon runs (see CV fall Chinook salmon account, Moyle 2002, Williams 2006), although it is much less well known in its details because of its comparatively recent recognition and its tendency to ascend and spawn at times when the Sacramento River is most likely to be high, cold, and turbid, making the fish hard to study. In the past, these migrating fish were a mixture of age classes, ranging from two to five years old. At the present time a majority of the fish are probably three-year olds. Late-fall Chinook mostly migrate upstream in December and January as mature fish, although they have been recorded from November through April (Williams 2006). Spawning occurs mainly in late December and January, shortly after the fish arrive on the spawning grounds, although it may extend into April in some years (Williams 2006). Emergence from the gravel starts in April and all fry have usually emerged by early June. The juveniles may hold in the river for 7-13 months before moving out to sea. Peak migration of smolts appears to be in October. However, there is evidence that many migrate out at younger ages and smaller sizes. Williams (2006) indicates that if DFG size criteria are used, downstream migrating late-fall Chinook can be found in most months of the year.

Habitat Requirements: 

Habitat Requirements: The specific habitat requirements of late-fall Chinook have not been determined, but they are presumably similar to other Chinook salmon runs and optimal conditions fall within the range of physical and chemical characteristics of the unimpaired Sacramento River above Shasta Dam. See the CV fall Chinook salmon account for details on temperature and other requirements. For a more specific summary of Central Valley Chinook salmon requirements see Stillwater Sciences (2006) and Moyle (2002).

Distribution: 

Distribution: Currently, CV late-fall Chinook are found mainly in the Sacramento River, where most spawning and rearing of juveniles takes place in the reach between Red Bluff Diversion Dam (RBDD) and Redding (Keswick Dam). However, varying percentages of the total run spawn downstream of RBDD in some years. In 2003, for example, 3% of the fish spawned below the dam, while in 2004 no fish spawned below the dam (Kano 2006a, b). R. Painter (DFG, pers. comm., 1995) indicated that late-fall Chinook have been observed spawning in Battle Creek, Cottonwood Creek, Clear Creek, Mill Creek, Yuba River and Feather River, but these are presumably at best a small fraction of the total population. The Battle Creek spawners are likely derived from fish that originated from the Coleman National Fish Hatchery. The historic distribution of CV late-fall Chinook is not well documented, but they most likely spawned in the upper Sacramento and McCloud rivers in reaches now blocked by Shasta Dam, as well as in sections of major tributaries where there was adequate cold water in summer. There is also some evidence they once spawned in the San Joaquin River in the Friant region and in other large San Joaquin tributaries (Yoshiyama et al. 1998).

Abundance Trends: 

Trends in Abundance: The historic abundance of CV late-fall Chinook is not known because it was recognized as distinct from fall Chinook only after Red Bluff Diversion Dam (RBDD) was constructed in 1966. In order to get past the dam, salmon migrating up the Sacramento River ascend a fish ladder in which they could be counted with some accuracy for the first time. The four Chinook salmon runs present in the river (fall, late-fall, winter, spring) were revealed as peaks in the counts, although salmon passed over the dam during every month of the year. In the first 10 years of counting (1967-1976) the late-fall run averaged about 22,000 fish; in the next 10 years (1982-1991) the run averaged about 9,700 fish (Yoshiyama et al. 1998). Since 1991, estimates of abundance are less accurate but in 1992-2007, total numbers were estimated to have averaged 20,777 fish, with a wide range in annual numbers, including a 1998 production total of over 80,000 fish. The less accurate counts were the result of opening the gates at Red Bluff for free passage of the listed winter Chinook salmon from September 15 to May 15 starting in 1992. This made estimation of late-fall Chinook spawner numbers more difficult because most of the fish could not be counted while ascending the fish ladders as they had been previously. In 1992-1996, estimates were made by extrapolating from counts of only part of the run. These numbers are extremely low and unreliable (Figure 1). In 1998, DFG initiated surveys based on carcass and redd counts from airplanes and estimated that over 35,000 late-fall Chinook had spawned above Red Bluff Diversion Dam. Subsequent surveys have resulted in lower estimates (e.g. 5,000 in 2003) but with variability from year to year. The numbers seem to indicate that measures taken to benefit winter Chinook salmon have probably also benefited late-fall run. It is possible that fish from Coleman National Fish Hatchery on Battle Creek are contributing to the spawning population in the main stem Sacramento River (Figure 2).

Description: 

Description: Central Valley late-fall Chinook salmon are morphologically similar to other Chinook salmon (see Central Valley fall Chinook account). They tend to be larger than other Central Valley Chinook salmon, reaching 75-100 cm TL and weighing up to 9-10 kg or more.