Lo et al Biomass and reproductive status of Sardinops sagax off the Pacific coast. 
185 
but this was primarily due to the bias correction based 
on the bootstrap simulation and the difference was not 
statistically significant. 
The relatively large 2003 year class constituted a 
major proportion of the total biomass in March 2004, 
whereas the 2004 year class constituted a very small 
proportion of the fish in 2005 (Fig. 6). Therefore, the 
relative abundance of Pacific sardine in the spring of 
2004 and 2005 was primarily supported by the strong 
year class of 2003. 
Spawning habitat 
The spawning habitat was located east of 125. 5°W longi- 
tude in July 2003 and 2004 (Figs. 2 and 4), and between 
43° and 44.5°N latitude in July 2003, and between 42° 
and 44.5°N latitude in July 2004. The location of the 
spawning center, computed as the weighted latitude and 
longitude with the eggs/min (>0.5) as the weight, was 
124. 7°W and 43.7°N in 2003 and 125.13°W and 42.9°N 
for 2004. Therefore, the spawning habitat shifted south- 
westward from 2003 to 2004. Because the eggs from the 
CUFES samples were distributed more to the west, the 
size of the spawning habitat was 10,716 km 2 for 2003 and 
14,260 km 2 for 2004. The spawning habitat, determined 
from CUFES data, crossed the dividing line of 125°W 
between two strata based on trawl allocation. For both 
July cruises, the range of SST in the spawning habitat 
was 13.4-18.5°C with a mean close to 16°C (15.7°C and 
16.0°C for 2003 and 2004). Note that the overall mean 
SST for July 2003 was 16.2°C (range 9.4-25.3°C) and 
the mean temperature was 16.8°C (range 9.7-19.9°C) 
in July 2004. The number of positive CUFES samples 
was 117 out of 482 in July 2003 and 129 out of 647 in 
July 2004. Therefore, the proportion of positive samples 
(24% in 2003, 19% in 2004) was similar during these 
two years. 
Daily egg production 
The mean density of eggs was 0.388 eggs/0.05 m 2 
(CV=0.51) in stratum 1 and no eggs were caught by 
CalVET net tows in stratum 2 during the July 2003 
survey. The opposite was true for the July 2004 survey: 
no eggs were caught in stratum 1 and the mean density 
in stratum 2 was 0.088 eggs/0.05 m 2 (CV=0.56) (Table 
3). The overall mean densities were 0.073 eggs/0.05 m 2 
(0.51) and 0.07eggs/0.05 m 2 (0.49) for 2003 and 2004, 
respectively. The bias-corrected estimates of the daily 
egg production from the integral method (P 0c ) (Eqs. 
5 and 6) in July were 0.04 eggs produced/0.05 m 2 / 
day(CV=0.51) for 2003 and 0.037 eggs produced/0.05 
m 2 /day (CV=0.58) for 2004. The mean egg capture 
rates from CUFES samples for 2003 and 2004 were 
0.069 eggs/min (CV=0.49) and 0.1 eggs/min (CV=0.53) 
(Table 3). 
The ratio of the total egg production in the PNW to 
the total egg production off the U.S. west coast (PNW 
and California) was 1.46% and 2.2% for 2003 and 2004 
and therefore Pacific sardine off the PNW contrib- 
uted approximately to 1.8% of the total egg production 
(Table 5). 
Adult sardine reproductive parameters 
and spawning biomass 
During the four surveys, 92 of the 214 trawls (Figs. 2-5, 
Table 1) captured adults or subadults. In the random 
subsamples from these trawls, 2862 sardine were mea- 
sured (Fig. 6); standard length ranged from 99-289 mm 
for females, 106-281 mm for males, and 75-146 mm for 
individuals of indeterminate sex (where it was difficult 
to accurately determine sex without microscopic exami- 
nation). Nearly all females were mature in July 2003 and 
nearly all were immature in March 2004 (Table 4). Using 
logistic regression we computed the standard length at 
which 50% were mature as 195.1 mm and 199.8 mm for 
July 2004 and March 2005, respectively (Fig. 7). 
Mean batch fecundity was estimated for 35 females 
caught in July 2003 and 19 from July 2004 (Fig. 8). 
Analysis of covariance showed no differences in the 
relationship between female weight (without ovary, W 0 f) 
and batch fecundity (F b ) among years (P=0.531). Com- 
bining the data from July 2003 and 2004, we found 
that the relationship between female weight and batch 
fecundity, as determined by simple linear regression, 
was F ft = -16755 + 372.1W o/ with the r 2 = 0.47. Because 
the intercept did not differ from zero (P=0.165), we 
chose the regression without the intercept, which yield- 
ed the relationship F b = 295.83W o ^ , where W ’<■ ranged 
from 111-322 g (Fig. 8). The latter equation was used 
to calculate batch fecundity for each mature Pacific 
sardine female in the July trawl samples. 
The population sex ratio ( R ) for mature fish was 
0.534 female (CV=0.04) in July 2003 and 0.568 female 
(CV=0.05) in July 2004 (Table 5). The 657 mature fe- 
male Pacific sardine analyzed from July 2003 and 196 
from July 2004 were considered a random sample of 
the population in the area trawled. Population-level 
estimates of the other adult reproductive parameters 
were as follows: average batch fecundity {F)= 55,986 
eggs/spawning event (CV=0.04) in July 2003 and 
55,883 eggs/spawning (CV=0.06) in July 2004; daily 
spawning fraction (S) = 0.027 (CV=0.31) in 2003 and 
S = 0.010 (CV=0.74) in 2004; and mean mature female 
fish weight (W^= 194.36 g (CV=0.02) in 2003, and 193.16 
g (CV=0.03) in 2004 (Table 5). The daily specific fecun- 
dity was calculated as 4.21 and 1.68 eggs/gm/day in 
2003 and 2004, respectively (Table 5). The proportion 
of active females spawning was 0.05 and 0.025 for July 
2003 and 2004, respectively, which meant that the av- 
erage female was spawning roughly once every 20 to 
40 days. None of the three mature females caught in 
March 2004 or the 37 mature females caught in March 
2005 had histological evidence of imminent or recent 
spawning (hydrating oocytes or postovulatory follicles), 
and thus S = 0; hence, spawning biomass was not esti- 
mated for either March (Table 5). 
The estimated spawning biomass based on biased 
corrected egg production from the integral method (P 0 c ) 
