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Fishery Bulletin 108(2) 
results, which indicated that the majority of the tags 
released off the PNW were recovered off central Cali- 
fornia (Clark and Janssen, 1945). 
The point estimates of spawning biomass of Pacific 
sardine off the PNW differed, but were not statistically 
different because of a large coefficient of variation: 
39,184 t and 84,120 t for July 2003 and 2004, respec- 
tively. They were close to 50,000 t in 1994 (Bentley et 
al., 1996). Theoretically, the spawning biomass should 
constitute a good proportion of the total biomass, which 
was not so for July 2003. This could be due to an under- 
estimate of P 0 , to an overestimate of the spawning frac- 
tion, or both. The overestimate of the spawning fraction 
could be due to the movement of the postspawners out of 
the spawning area. A DEPM study is needed to evaluate 
such effects and model the effects of fish movement on 
estimates of spawning rate. The effect of the timing of 
the survey in relation to spawning and movement cycles 
needs to be studied with new data and modeling. 
The difference between the spawning biomass es- 
timates in 2003 and 2004 was primarily due to the 
difference in the estimated spawning fractions (0.027 
in contrast to 0.01), because the estimates of daily egg 
production (P 0 ) were similar. The large coefficients of 
variation of spawning biomass estimates were mainly a 
result of the uncertainty in estimates of P 0 and the dai- 
ly spawning fraction (S) in July 2004. For low values of 
P 0 and S, the number of samples has to be substantially 
increased to obtain a more precise estimate (Picquelle 
and Stauffer, 1985). Estimated spawning biomass for off 
the PNW in July was much smaller than estimates for 
off California during April in recent years. The smaller 
fish length at 50% maturity off California means that 
the more numerous smaller resident Pacific sardine are 
able to participate in local spawning at the same time 
as the larger migratory sardine. 
Future work 
The Pacific sardine spawning habitat and season in the 
PNW are loosely defined in this study and the magnitude 
and scope of the coastal migration are not fully explored. 
To better characterize these, we need to conduct syn- 
optic trawl-ichthyoplankon-acoustic surveys from Baja 
California, Mexico, to British Columbia, Canada, during 
spring and early summer at three to five year intervals. 
To better characterize the spawning habitats in this 
area, we need to obtain physical and biological oceano- 
graphic data (Lynn, 2003; Emmett et al., 2005; Reiss et 
al., 2008) and demographic data of Pacific sardine over 
a broader geographic range because the Pacific sardine 
is a migratory species. 
For trawl swept-area-based biomass estimates, the 
efficiency of the trawl needs to be calibrated. Biomass 
estimates from acoustic surveys would be another fish- 
ery-independent source of relative abundance. Because 
the coefficients of variation of all estimates are large, 
the number of trawls needs to be increased or other 
statistical estimation procedures should be explored, or 
both, to improve the precision of estimates. To obtain 
a representative length distribution of the population, 
fishery-independent surveys covering the whole west 
coast area are essential, and length data from com- 
mercial vessels should be used with caution for both the 
PNW and California. For spawning biomass, we need to 
understand the maturation schedules of females and the 
spawning season off Oregon and Washington. Numerous 
plankton net tows are needed to obtain direct estimates 
of the daily egg production and egg mortality rates in 
early summer. Currently, only the spawning biomass 
of Pacific sardine off California is estimated from the 
annual April DEPM survey. Because mature females 
were caught during two March surveys off the PNW, 
efforts should be made to obtain trawl data off the 
PNW in April. Data for mature females collected off the 
PNW could then be combined with the April data set 
off California to estimate reproductive parameters and 
the spawning biomass of Pacific sardine off the whole 
west coast of the United States. To better understand 
the relationship between the sardine populations off 
California and the PNW, we need to examine migration 
characteristics (i.e, migration range, pattern and sched- 
ule) and the effect of fishing pressure on the migratory 
fish because most of these fish are mature and leaders 
of migration imprints. We need a long time series of 
abundance for all regions together, along with ocean- 
ographic and biological data, to enhance our under- 
standing of the dynamics of the entire Pacific sardine 
population to provide information for the development 
of future strategies to sustain the population. 
Acknowledgments 
We thank two anonymous reviewers for their construc- 
tive comments. We thank the captain and crew members 
of the FV Frosti and the support for the charter provided 
by NMFS Cooperative Research Program. These surveys 
would not have been possible without the cooperation 
of the Northwest Fisheries Science Center, NOAA, the 
Washington Department of Fish and Wildlife (WDFW), 
Oregon Department of Fish and Wildlife (ODFW), 
and the Pacific Fishery Management Council (PFMC). 
We thank all those who participated in the surveys: 
D. Waldeck (PFMC), Todd Miller (Oregon State Univer- 
sity), J. McCrae (ODFW), A. Thurman (WDFW), and E. 
Acuna and N. Bowlin of Southwest Fisheries Science 
Center. We thank J. Hunter, W. Watson, S. Picquelle, E. 
Dorval, K. Hill, A. Takasuka, S. McClatchie, A. MacCall, 
E. Weber, and R. Emmett for reviewing the manuscript 
and R. Sanford for organizing the manuscript. 
Literature cited 
Ahlstrom, E. H. 
1948. A record of pilchard eggs and larvae collected 
during surveys made in 1939 to 1941. U.S. Fish Wildl. 
Serv., Spec. Sci. Rep. no. 54, 76 p. 
