Lo et al. Biomass and reproductive status of Sardmops sagax off the Pacific coast. 
175 
the importance of the PNW as a spawning area 
has not been studied. After the resurgence of 
Pacific sardine off California, ichthyoplankton 
and fishery-independent trawl surveys have been 
conducted off California to assess the biological 
characteristics of the sardine population since the 
mid 1980s, when the estimated sardine biomass 
approached 20,000 t (Wolf, 1992; Lo et al., 2005). 
Beginning in the mid 1990s, sardine abundance, 
distribution, and ecological relationships off the 
PNW and Canada were analyzed with data from 
salmon surface-rope trawl surveys off the PNW 
and trawl surveys off Vancouver Island, Canada 
(Bentley et al., 1996; Emmett et al., 2005; Mc- 
Farlane et. al., 2005); however, very few of those 
surveys were designed specifically to assess the 
biological characteristics of Pacific sardine. 
Four trawl surveys off the PNW were conducted 
in July 2003, March and July 2004, and March 
2005 to provide fishery-independent measures of 
biological characteristics of sardine in this area, 
and to answer the following questions: 1) Do sar- 
dine migrate between the PNW and California? 
2) To what extent does Pacific sardine spawning 
in the PNW depend on the sardine population off 
California? and 3) How much does the Pacific sar- 
dine egg production in the PNW contribute to that of the 
whole population? To answer these questions, we esti- 
mated spring and summer biomasses with length distri- 
butions to serve as signals of migration; the location and 
spatial extent of spawning habitat to examine the fol- 
lowing: the effect of the reduction of the spawning area 
in the PNW to the local population; daily egg production 
and its contribution to the total egg production; adult 
reproductive parameters to estimate rates of spawning, 
fecundity and maturity; and spawning biomass. These 
measurements were compared with available PNW mea- 
surements from the mid-1990s and those off California 
in the same time period, to facilitate our understanding 
of the population dynamics of the Pacific sardine off 
the northern west coast of the North American con- 
tinent, and to better manage the entire population. 
Materials and methods 
Survey 
In order to obtain unbiased estimates of the biologi- 
cal characteristics of Pacific sardine off the PNW, the 
Fisheries Resources Division of the Southwest Fisheries 
Science Center, conducted four surveys in July 2003, 
March and July 2004, and March 2005 aboard the FV 
Frosti. Multiple gear types were used: a surface trawl to 
collect adult samples, the CalVET plankton net (Califor- 
nia Cooperative Oceanic Fisheries Investigation verti- 
cal-egg-tow net; Smith et al., 1985), and the continuous 
underway fish egg sampler (CUFES; Checkley et al., 
1997) to collect ichthyoplankton samples and record 
hydroacoustics. The survey region encompassed the area 
of the northeast Pacific Ocean from 42° to 48°N latitude 
and from inshore out to 128°W longitude. 
The basic survey pattern comprised seven transect 
lines oriented on the parallels at a spacing of 60 nauti- 
cal miles (111 km). Stations were spaced at 30 nautical 
miles (55.5 km) along each transect measured from 
the offshore station. Forty-two predetermined stations 
were sampled by trawl and CalVET tow during each 
survey. For the July 2003 survey, the primary goal was 
to estimate the spawning biomass of Pacific sardine. In 
the offshore area, few trawls were undertaken because 
both acoustics and CUFES samples showed little sign 
of sardine schools and eggs. The inshore sampling was 
discontinued close to the 100-m isobath during July 
2003 to avoid net damage in shallow water. All fish- 
ing was conducted at night, when Pacific sardine are 
distributed in the upper 50 m of the water column and 
oceanographic conditions at depths greater than 50 m 
would have little influence on the spatial and vertical 
distributions of sardine schools. Moreover, within 60 km 
from the shore, the densities of fish were not related to 
the distance from shore (Emmett et al., 2005). Therefore 
we expected little bias introduced from sampling along 
the 100-m isobath. With more experience, we found that 
we could tow the net at a shallower depth than initially 
expected, and during subsequent surveys we occasion- 
ally fished inshore at shallower depths (see below, Figs. 
2-5). For the remaining three surveys, most trawls 
were evenly distributed along the transect line and be- 
tween transect lines in the inshore area. Occasionally, 
trawls were made during transit between transect lines. 
Both trawl and CalVET samples were collected dur- 
ing all four surveys and CUFES samples were collected 
during July surveys only (Figs. 2-5). Trawl-related 
