342 
Fishery Bulletin 113(3) 
Figure 1 
Map of the central California coastline, with the northern boundaries of 
the San Francisco (SF) and Monterey (MO) management areas denoted 
by dashed lines. 
how exploitation has varied historically. This general 
condition applies to both target stocks in fisheries, as 
well as ESA-listed stocks that are taken in fisheries 
as incidental catch. 
Sacramento River winter Chinook salmon (On- 
corhynchus tshawytscha) (SRWC), named for the season 
of freshwater spawning return, were first listed under 
the ESA in 1989 as threatened and then as endangered 
in 1994 (Federal Register, 1994). The Sacramento River 
winter Chinook Evolutionarily Significant Unit, cur- 
rently composed of a single population that spawns in 
the Sacramento River downstream from Keswick and 
Shasta dams near Redding, California, has experienced 
a heavy decline in abundance (Fisher, 1994; Yoshiyama 
et al., 1998). Fisher (1994) reported a potential maxi- 
mum spawning run size of 200,000 before dam con- 
struction and a spawning stock estimate of more than 
100,000 fish in the late 1960s (after dam construction). 
Estimates published by the Pacific Fishery Manage- 
ment Council (PFMC) (PFMC 2 ) indicate a run size of 
more than 30,000 fish in the early 1970s and run sizes 
below 1000 fish for several years since 1980. 
The time series of exploitation rates estimated for 
SRWC is much shorter than the time series for escape- 
ment. O’Farrell et al. (2012a) used cohort reconstruc- 
tion methods (Hilborn and Walters, 1992) to estimate 
broad year exploitation rates, referred to as the spawn- 
er reduction rate and defined as the reduc- 
tion in a brood’s potential adult spawner es- 
capement that is caused by ocean fisheries 
in relation to escapement potential in the 
absence of ocean fishing. A cohort-recon- 
struction model was applied to data gener- 
ated from the SRWC marking (with adipose 
fin clips) and tagging (with coded-wire tags) 
program initiated at Livingston Stone Na- 
tional Fish Hatchery in 1998. Before 1998, 
hatchery supplementation of SRWC was 
sporadic and the marking and tagging data 
were insufficient for estimation of exploita- 
tion rates. The impact rate for age-3 SRWC 
(hereafter referred to as the impact rate ) 
is a measure of the fishing mortality rate 
on age-3 fish that corresponds closely to 
the exploitation rate for SRWC. The corre- 
spondence between the brood-year exploita- 
tion rate and the impact rate is due to the 
very high maturation rates of age-3 SRWC 
that result in few age-4 fish remaining in 
the ocean to contribute to catch or spawner 
escapement (O’Farrell et al., 2012a). The 
impact rate is estimated annually and pub- 
lished in PFMC reports (e.g., PFMC 3 ). 
Although the estimated impact rates quantify the 
recent (during and after the year 2000) salmon fish- 
ing-induced mortality (hereafter “fishery mortality”) 
on SRWC, this period follows the implementation of 
conservation measures designed to reduce impacts on 
SRWC and changes in ocean fisheries owing to man- 
agement measures intended for other stocks. Salmon 
fisheries south of Point Arena, California (Fig. 1), are 
responsible for the vast majority of SRWC harvest 
(O’Farrell et al., 2012a; Satterthwaite et al., 2013), and 
many of the constraints on fisheries in this region have 
been intended to protect SRWC. For example, recre- 
ational fisheries in this region routinely began in mid- 
February, but since the early 1990s the starting date 
gradually moved later in the year. Since 2004, no fish- 
eries have occurred in February or March. Increased 
minimum size limits (e.g., >20 in [51 cm] in total 
length) have been imposed on the recreational sector 
in an effort to reduce retention of SRWC. For a vari- 
ety of reasons associated with increased constraints on 
ocean fishing that have resulted from ESA listings and 
river (versus-ocean) allocations of harvest, the com- 
mercial sector has seen a reduction in participation of 
vessels with California salmon permits since the early 
1980s (PFMC 2 ). The time series of commercial and rec- 
reational fishing effort south of Point Arena (Fig. 2) 
indicates that substantial changes in ocean fishery ef- 
2 PFMC (Pacific Fishery Management Council). 2014. Re- 
view of 2013 ocean salmon fisheries: stock assessment and 
fishery evaluation document for the Pacific coast salmon fish- 
ery management plan, 371 p. (Document prepared for the 
Council and its advisory entities.) Pacific Fishery Manage- 
ment Council, Portland, OR [Available at website.] 
3 PFMC (Pacific Fishery Management Council). 2015. Pre- 
season report I: stock abundance analysis and environmental 
assessment part 1 for 2015 ocean salmon fishery regulations, 
135 p. (Document prepared for the Council and its advisory 
entities.) Pacific Fishery Management Council, Portland, 
OR. [Available at website.] 
