Lo et al. Biomass and reproductive status of Sardinops sagax off the Pacific coast. 
187 
summer to feed, and a return to the south before 
spring to spawn (Clark and Janssen, 1945; Dorn, 
1995; Emmett et al., 2005; Smith, 2005). 
The U.S. stock biomass of age 1+ Pacific sardine 
increased from 1981 to a peak of one million tons 
in 2000 and, according to the stock assessment, 
began to decline in 2003 (Hill et al., 2007). The 
high biomass off the PNW in 2003 was most likely 
due to the accumulation of migrant survivors from 
1999 through 2002, when the stock assessment 
reported that biomasses were high. The PNW sar- 
dine biomass, estimated from surface rope-trawl 
surveys for salmon off the Columbia River, has 
been decreasing since 2003 (R. Emmett, personal 
commun. 2 ). This decrease is likely due to 1) the 
decline of migratory fish as a result of the de- 
creasing biomass since 2003 off California, 2) a 
decline in successful spawning off the PNW, or 3) 
the continued sardine movement northward into 
Canadian waters, or a combination of the three 
events. 
The July 2003 survey indicated that the major- 
ity of fish were large (>190 mm SL), whereas the 
July 2004 survey showed the opposite because 
most of the small fish were from the strong 2003 
year class. The presence of large sardine off Or- 
egon in July 2003 and California in March-April 
2004 is consistent with the concept of the migra- 
tion of large fish from the PNW to California 
before spawning. However, the large sardine off 
Oregon in July 2004 did not show up off either 
California or the PNW during March-April 2005 
(Fig. 6). This finding may have been due to a 
lower total biomass and a smaller proportion of 
large fish off the PNW in July 2004 (Table 1, Fig. 
6), or because during the 2005 California survey, 
few trawls were taken north of 34°N latitude 
where most migrants had resided according to 
the 2004 DEPM survey off California, or it could 
have been due to a combination of both factors 
(Fig. 5). 
Although the summer PNW biomass estimates 
were different between years, the spring biomass 
estimates were stable. March surveys clearly revealed 
the relative magnitude of the migratory and the local 
PNW stocks during the survey years. The change in 
biomass off the PNW among years can be due to mul- 
tiple reasons: a change in the biomass of the resident 
PNW fish, or a change in the biomass off California, or 
a change in the migration pattern due to food availabil- 
ity and oceanographic conditions, or both (MacFarlane 
et al., 2005). To better understand the dynamics of the 
Pacific sardine off the west coast of North America, 
spring and summer synoptic surveys from Baja Cali- 
fornia, Mexico, to British Columbia, Canada, and from 
tagging studies are necessary. 
2 Emmett, Robert. 2009. Northwest Fisheries Science Center, 
Newport, OR. 
Figure 7 
Fraction of Pacific sardine ( Sardinops sagax) females that 
were sexually mature (y) as a function of standard length (L) 
fitted to logistic curves for Oregon and Washington in July 
2004 and March 2005, and for California in April of 1994, 
2004, and 2005. Symbols represent the actual fraction mature 
within 10-mm length classes. 
Spawning habitat and daily egg production 
The spawning habitats off the PNW in the summer of 
2003 and 2004 were similar in size between 42-44. 5°N 
and east of 125. 4°W. The spawning area occupied 5-7% 
of the survey area, much smaller than that off California 
(20-25% of the survey area in 2003-04). The spawning 
habitat in the mid-2000s (2003 through 2005) seemed to 
contract southward and shoreward compared to the mid- 
1990s (1994 through 1998) when it extended to 46°N and 
close to 126°W (Emmett et al., 2005). The temperature 
range in the offshore spawning habitat in the 1990s 
(14-16°C) was similar to that in the 2003-04 inshore 
area (13— 18°C); therefore, the change of oceanographic 
conditions may have caused the apparent contraction of 
spawning habitat between the mid-1990s and mid-2000s 
off the PNW. Because no adult samples were taken in 
the mid-1990s, we were unable to compare the adult 
