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Fishery Bulletin 108(2) 
or the fraction of mature females spawning per day; the 
average batch fecundity (number of eggs per spawning 
per mature female: F ); the fraction of mature fish that 
were female by weight (sex ratio: R ); and the average 
weight of mature females (g) (WJ. The reproductive 
parameters were estimated from the data on the first 
25 mature females per trawl or all mature females if 
there were <25 by following the methods in Macewicz 
et al. (1996). Females with ovaries histologically iden- 
tified as containing hydrated oocytes (hydrated ovary) 
have temporarily inflated ovary weights. For each July 
survey, the relation between wet weight (y) and ovary- 
free wet weight (x) from mature females lacking hy- 
drated oocytes was determined as y=-9.0998 + 1.0758x 
in 2003 and y=-6.316 + 1.05608x in 2004. Thus, the 
observed female weight was adjusted downward for fe- 
males with hydrated ovaries when calculating average 
mature female weight (Wf) for each collection by year. 
During March of 2004 and 2005, adjustments were not 
necessary and fecundity was not estimated from mature 
females caught because none of them had ovaries with 
oocytes in the migratory-nucleus or hydrated stages. 
Mean batch fecundity was estimated by the gravimet- 
ric method for 54 females from 21 trawls from the July 
surveys. The relationship of batch fecundity to female 
weight (without ovary) was then determined. 
Reproductive adult parameters were summarized for 
each trawl. Population values were estimated by meth- 
ods in Picquelle and Stauffer (1985), where estimation 
of each adult parameter (S, F, W, R) was based on a 
ratio estimator (Picquelle and Stauffer, 1985; Lo et ah, 
1996) and used to calculate spawning biomass and its 
covariance for the July 2003 and July 2004 surveys. 
Spawning biomass 
The denominator (. RSF/W * ) is referred to as the daily 
specific fecundity (number of eggs/population weight 
[g]/day). 
The variance of the spawning biomass estimate (B s ) 
was computed from the Taylor expansion in terms of 
the coefficient of variation (CV) for each parameter 
estimate and covariance for adult parameter estimates 
(Parker, 1985; Picquelle and Stauffer, 1985; Lo et al., 
1996; 2005): 
var(b s )=b s 
cv(p 0 f +cv(w / .) 2 +cv(s ) 2 + 
cv (r) 2 + CV (f) 2 + 2 covs 
( 8 ) 
The last term, involving the covariance term, on the 
right-hand side is 
COVS = 
i i<j 
COV ( Xj , Xj j 
x t x- 
(9) 
where x ; =the z'th adult parameter estimate, e.g., x t =F 
and Xj=Wf. The sign of any two terms is positive if they 
are both in the numerator of B s or denominator of B s 
(Eq. 7); otherwise, the sign is negative. The covariance 
term is 
COV( Xj Xj ) 
[n I (n-l)\^m k {x lk - x^g^Xj k - Xj) 
* , (10) 
( \ 
( \ 
x** 
V k , 
\ k J 
The DEPM is a well-accepted method used for estimating 
spawning biomass for fish with indeterminate fecundity, 
i.e. multiple spawners (Hunter and Lo, 1993; Stratouda- 
kis et al., 2006) and was used to estimate the spawning 
biomass of Pacific sardine in this area in 1994 (Bentley 
et al., 1996). The spawning biomass was computed with 
the following equation: 
where k = k th tow, and k=l, ... , n\ 
m k and g k = sample sizes; and 
x £ k and Xj k = sample means from the k th tow for x ; and 
Xj respectively. 
Results 
, PqAC 
>s RSF/W f 
(7) 
where P 0 = 
A = 
C = 
R = 
S = 
F = 
the daily egg production/0.05 m 2 at hatch- 
ing; 
the survey area in units of 0.05 m 2 ; 
the conversion factor from grams (g) to 
metric tons (t); 
the fraction of mature fish that is female, by 
weight (sex ratio); 
the daily spawning fraction: fraction of 
mature females spawning per day; 
the average batch fecundity (number of eggs 
per spawn per mature female); and 
the average weight of mature females (g). 
Seasonal biomass 
The relative abundance of Pacific sardine was higher 
in summer than in the following spring off the PNW. 
The bias-corrected seasonal biomass estimates were 
198,600 t (CV=0.51) for July 2003, 20,100 t (CV=0.80) 
for March 2004, 77,900 t (CV=0.38) for July 2004, and 
30,100 t (CV=0.72) for March 2005 over an area close 
to 200,000 km 2 (Table 1). The inshore stratum 1 made 
up 20% of the survey area. Yet, for all years stratum 1 
had over 80% of the biomass. The recruit biomasses (fish 
<120 mm SL) in spring of 2004 and 2005 were quite dif- 
ferent: 20,500 t (CV=0.81) for the 2003 year class and 
53 t (CV=0.72) for the 2004 year class, respectively. The 
2004 point estimate of the recruit biomass, 20,500 t, 
was greater than that of the total biomass of 20,100 t 
