344 
Fishery Bulletin 113(3) 
c t,z,x — A;,z,x x /t,z,x- (3) 
The number of fish contacted (C) is computed by mul- 
tiplying the oceanwide abundance of the SRWC age-3 
cohort by the contact rate: 
Ct,Z,X = c t,z,x X -^t) (4) 
where contacts represent the number of fish that en- 
countered the fishing gear and were retrieved to the 
boat. Impacts are the sum of harvest, release, and 
dropoff 
mortality: 
^t,Z,X = Ht,Z,X + “St.Z.X + ^t,Z,X 
(5) 
where 
Ht,Z,X — C t,z,x x P t,z,x> 
(6) 
^t,Z,X — 1C(; <Z ,X — fft,Z,x) X S t,Z,X5 
(7) 
and 
^t,Z,X — Ct jZ>x x d. 
(8) 
In these equations, release and dropoff mortality rates 
are denoted by s and d, respectively, and p is the esti- 
mated proportion of the cohort that is greater than or 
equal to the legal size for retention in the fishery. 
Data, parameters, and variables 
Effort in California ocean salmon fisheries was es- 
timated by the California Department of Fish and 
Wildlife (CDFW) on the basis of landing receipts from 
the commercial sector and dockside samples from 
the recreational sector. Units of fishing effort are the 
number of vessel days (the number of days fished by 
commercial salmon vessels) for the commercial sector 
and number of angler days for the recreational sector. 
Fishing effort for the years 1978-2012 are reported in 
PFMC 2 and an electronic record of the historical ocean 
salmon fishery effort and landings for the U.S. West 
Coast (PFMC 5 ), maintained by the PFMC. Records of 
minimum size limits in California ocean fisheries for 
the years 1978-2012 were obtained from PFMC 2 and 
an electronic record of the historical ocean salmon fish- 
ery regulations for the U.S. West Coast (PFMC 6 ), main- 
tained by the PFMC. 
Coded-wire tag recovery data from ocean and river 
sampling programs were used in cohort reconstruc- 
tions for SRWC to estimate contact and impact rates in 
ocean fisheries for the years 2000-2012, following the 
methods described in O’Farrell et al. (2012a). Cohort 
reconstruction is the sequential estimation of a cohort’s 
abundance from the end of that cohort’s life span, when 
abundance is zero, to a specified earlier age (commonly 
age 2). Age-specific spawner escapement and harvest 
5 PFMC (Pacific Fishery Management Council). 2014. Ocean 
salmon fishery effort and landings (Review Appendix A). Ex- 
cel workbook. PFMC, Portland, OR. [Available at website.] 
6 PFMC (Pacific Fishery Management Council). 2014. Ocean 
salmon fishery regulations and chronology of events (Review 
Appendix C). PFMC, Portland, OR. [Available at website.] 
data are required, and natural mortality rates are as- 
sumed. Fishery contacts stratified by age, month, man- 
agement area, and fishing sector were computed by 
expanding the harvest by the estimated proportion of 
SRWC expected to be larger than or equal to the mini- 
mum size limit (C = H/p). Given an estimate of C, and 
the estimated abundance N, the contact rate was esti- 
mated by rearranging Equation 4 as follows: c = C/N. 
The impact rate was estimated from cohort reconstruc- 
tion in the same manner as that shown in Equation 2. 
It was implicitly assumed that contact and impact 
rates estimated from tagged, hatchery-origin fish are 
representative of the natural-origin SRWC population. 
Although it is difficult to directly evaluate this com- 
mon assumption (PSC 7 ), there is some evidence that 
hatchery-origin indicator stocks have similar ocean dis- 
tributions and fishery exposure as those estimated for 
untagged stocks for which they serve as proxies (Weit- 
kamp and Neely, 2002; Satterthwaite et al., 2014). The 
hatchery-origin component of the total SRWC abun- 
dance is only a portion of the total abundance; for the 
years 2000-2010, the hatchery-origin component of fe- 
male SRWC spawners was <20% (Winship et al., 2014). 
Ocean salmon fisheries are sampled by the CDFW with 
a goal of sampling at least 20% of the harvest in each 
month, management area, and fishery sector. Heads are 
taken from all fish with a clipped adipose fin for coded- 
wire tag extraction and reading. A total of 4036 coded- 
wire tag recoveries were used in cohort reconstructions, 
554 of which were from ocean fisheries (commercial and 
recreational), whereas the vast majority of the remain- 
ing recoveries were from spawner escapement surveys. 
Recreational, river harvest of SRWC is rare because of 
closures to the Sacramento River salmon fishery during 
much of the migration and spawning period. 
Contact rates and fishing effort estimated for each 
month, area, and sector open to fishing in 2000-2012 
were used to calculate the contact rate per unit of ef- 
fort. For hindcasting purposes, values of the contact 
rate per unit of effort were derived for the entire peri- 
od of 1978 to 2012 with the application of the bootstrap 
method to the estimates of contact rates per unit of ef- 
fort for 2000-2012 (Efron and Tibshirani, 1993). These 
derived values of contact rate per unit of effort were 
then multiplied by the corresponding observed fish- 
ing effort for 1978-2012 to yield a set of contact rate 
hindcasts (Eq. 3). The bootstrap method used to char- 
acterize the contact rates per unit of effort is described 
later in the “Bootstrap” subsection. For strata for which 
these rates could not be estimated from available data 
sources, 2 methods were used to infer contact rates per 
unit of effort. 
Data sufficient for estimation of contact rates per 
unit of effort for recreational fisheries during Febru- 
ary and March are not available because recreational 
7 PSC (Pacific Salmon Commission). 2005. Report of the ex- 
pert panel on the future of the coded wire tag program for 
Pacific salmon. Pacific Salmon Comm. Tech. Rep. 18, 230 p. 
[Available at website.] 
