Lo et al. Biomass and reproductive status of Sardmops sagax off the Pacific coast. 
189 
grants, is essential because most of the migrants are 
mature fish and the leaders of migration imprints: older 
fish lead younger fish to migrate. This recent entrain- 
ment hypothesis (Petitgas et al., 2006) is a step for- 
ward from the theory that fish population life cycles are 
controlled only by physical conditions (Sinclair, 1988). 
The entrainment hypothesis implies that the older fish 
are essential to ensure the sustainability of popula- 
tion and fisheries of Pacific sardine off the PNW and 
thus along the entire west coast of the North American 
continent. 
Adult reproductive parameters and spawning biomass 
Pacific sardine spawn off the PNW, contrary to beliefs 
in the 1930s and 1940s that they spawn only off Cali- 
fornia. Although sardine eggs, larvae, and adults have 
been caught in surveys off the PNW since 1994 (Bentley 
et al., 1996; Emmett et al., 2005), only with the four 
surveys during 2003-05 were the reproductive param- 
eters for female Pacific sardine off the PNW examined 
in detail. 
The spawning season of Pacific sardine off the PNW 
apparently occurs primarily in the early summer, al- 
though a few fish possibly spawn in spring. If July 
is the spawning peak off the PNW, then spawning is 
less intense than during the peak off California in 
April. The daily spawning fraction of mature females 
(S=0.027 and 0.01) was much lower than that off Cali- 
fornia (0.07-0.17). Previous work has indicated that ac- 
tive mature females of Sardinops spp. worldwide spawn 
once every eight days (Macewicz et al., 1996). Recent 
results off California are similar (once every 6-8 days), 
where as active mature Pacific sardine females off the 
PNW spawned much less frequently (only once every 
20-40 days). In addition, females in July produced 
about 288 eggs per gram of female weight (relative 
batch fecundity) off the PNW — few eggs than similar 
females off California that spawned 334 eggs per gram 
of female weight in April 2004 (Table 5). According to 
the April 2004 DEPM sardine survey off California, 
the large mature females, in particular those >200 mm 
SL, were spawning very vigorously (S= 0.131) and these 
migratory females may not have recovered sufficient- 
ly to spawn at higher rates off the PNW during July 
2004, a phenomenon similar to that which occurred 
with Pacific sardine off Chile, which were less active 
during a second annual spawning period (Tascheri and 
Claramunt, 1996). The presence of a high percentage 
of inactive mature females off the PNW in July (43% 
in 2003 and 59% in 2004) indicates two other possible 
explanations for the low level of spawning: July is not 
the peak spawning time for sardine off the PNW be- 
cause they may be similar to northern anchovy where 
ovaries with high levels of atresia (indicating cessa- 
tion of reproductive activity) are common at the end 
of the spawning season (Hunter and Macewicz, 1985); 
or, Pacific sardine in the PNW may behave like chub 
mackerel (Scomber japonicus) whose individuals spawn 
only for a short period and inactive mature females are 
common throughout the spawning season (Dickerson et 
al., 1992). If so, it may be necessary in future surveys 
to analyze reproductive samples collected over a longer 
time to better define the peak spawning period, and to 
determine whether the peak spawning fraction is simi- 
lar to the rate off California (about 0.13 spawning per 
day) or whether it remains low (<0.03). 
Few mature Pacific sardine females were caught off 
the PNW during March and it seems that they may 
have followed warmer water south. The majority of the 
40 mature females were inactive (postbreeding or rest- 
ing) and none had spawned. It was surprising that we 
caught 12 females of 202-260 mm SL that were active 
(their ovaries contained some oocytes with yolk) and 
were potentially capable of spawning in the near future 
(3-30 days). We examined the locations where females 
were caught and their associated water temperatures. 
The average SST of trawls during March was 10.4°C. 
During March 2004, the three mature females (one 
active) were caught farthest south (42°N) in 11.1°C 
water. One inactive mature female was caught near 
Astoria, OR, in 11.1°C water during March 2005, and 
the other 36 (11 active) mature females were caught 
inshore, south of 44.5°N in 11.5°C (10.7-12.5°C) wa- 
ter. Immature female Pacific sardine were generally 
found north of 44.5°N in cooler water; on average 10.2°C 
(9.6-10.7°C) in March 2004 and 10.3°C (9.0-12. 5°C) in 
March 2005. Thus, in the winter, the older fish were 
able to move south following the warmer water, while 
the younger fish, due to a lack of stored energy for long 
distance swimming, remained in the cold water. Over- 
wintering immature females seem to tolerate water as 
cold as 9.0°C. The PNW generally has warmer coastal 
SSTs in the winter (from downwelling) than in summer. 
However temperatures in the estuaries can be very cold 
and die offs of age-0 sardine in the Columbia River and 
other estuaries have been observed during the winter 
(E. Dorval, personal commun. 3 ). 
Female Pacific sardine in the PNW mature at lengths 
greater than those off California. Fifty percent of the 
females caught off the PNW matured at around 195 
mm and > 90% off California were mature at the size 
of the smallest mature PNW female (182 mm). A major- 
ity of sardine > 200 mm off the PNW migrate during 
fall-winter (Clark and Janssen, 1945; Nottestad et al., 
1999). During the April 2004 DEPM survey, Pacific 
sardine were collected off central California between 
34.8°N and 37.3°N and a majority were the large, mi- 
gratory size (those >200 mm), whereas in 2005, the 
majority of positive adult samples were collected in the 
inshore area of Southern California between 32°N and 
36°N and most sardines were <200 mm. The length of 
females at 50% maturity off the PNW was similar to 
the length estimate (193 mm) in April 2004 off Cali- 
fornia which indicated that the large Pacific sardines 
off central California likely were winter migratory fish. 
This conclusion is consistent with the historical tagging 
3 Dorval, Emanis. 2008. Librairie La Lumiere, Rue Baussan, 
# 34, Turgeau, Port-au-Prince, Haiti, W.I. 
