A two-event mark-recapture experiment was used to estimate the abundance of Chinook salmon Oncorhynchus tshawytscha that returned to spawn in the Unuk River in 2009.
Abundance of large Chinook salmon (³660 mm MEF) was estimated to be 3,157 (SE = 354) in 2009. The estimates were made from 287 marked and 56 recaptured fish out of 624 examined upstream. Using indirect methods, abundance of fish 555–659 mm MEF was estimated to be 1,346 (SE = 180) and the abundance of fish <555 mm MEF was estimated to be 238 (SE = 45).
As part of a stock assessment program that began in fall 1993 (1992 brood year), coded wire tags (CWTs) were implanted in juvenile Chinook salmon on the Unuk River each fall and spring from 2005 to 2009. Harvest, harvest distribution, incidental harvest mortality, and total fishing mortality were estimated for the 1992–2006 brood year returns through 2009. Estimates of spawning abundance derived from the inriver mark-recapture studies (1994 and 1997-2009), escapement age-sex-length data (1995–2009), and CWT study results were used to estimate total production, marine survival, and exploitation rates for the 1992–2006 broods, through 2009.
The adipose fins of CWT-tagged fish were also excised as the first event in a two-event mark recapture study to estimate smolt abundance for the 1992–2006 broods. Smolt abundance and CWT release and recovery information were used to estimate parr abundance and the overwinter survival rate of Chinook salmon parr from the 1992–2006 broods.