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Fishery Bulletin 108(2) 
Figure 4 
(A) Locations of trawls (stars) used for biomass estimation of Pacific sardine ( Sardinops sagax), excluding added trawls 
in the inshore area (Table 1), and (B) California vertical egg tows (CalVET: circles) and continuous underway egg 
sampling in eggs/minute (CUFES: triangles) for 2004 July trawl-ichthyoplankton survey off the Pacific Northwest. 
Contours are sea surface temperatures (°C). The dashed vertical line is the 125°W longitude divider of the two sam- 
pling strata. The shaded area is the major spawning habitat. Positive tows were those tows during which sardine were 
caught. Negative tows were tows when sardine were not caught. 
abundances. A stratified sampling design was used 
to estimate biomass and spawning biomass, because 
more stations were assigned close to the shore than 
offshore. Otherwise, estimates would be biased toward 
the inshore area (Holt and Smith, 1979). The survey 
area was divided into an inshore area (stratum 1) and 
an offshore area (stratum 2) with 125°W longitude as 
the dividing line. For the July 2003 survey, we excluded 
the nonpredetermined trawls (i.e., those trawls locations 
of which were not determined before the survey) taken 
in the vicinity of positive trawls to prevent an overesti- 
mate of the total biomass. The catch for each tow was 
expressed as kg/m 2 ( = catch [kg]/swept areaT m 2 ]=catch 
[kg]/volume of water [m 3 ]/depth 20 m), where the volume 
of water filtered was computed as the distance covered 
by each tow multiplied by the area of the vertical trawl 
mouth opening of approximately 360 m 2 (with 20 m as 
diameter). We estimated relative total biomass (B) and 
its standard error (SE) for each survey as follows: 
S = ^ ( A, 10 6 ) / 1000, (1) 
i 
SE(B) = ( ^ ( var( X l ) (A, 10 6 ) 2 ) 1/2 / 1000 ( 2 ) 
i 
where B = the estimate of the total biomass (t); 
X i = the mean catch (kg/m 2 ); and 
