586 
Fishery Bulletin 95(3), 1997 
the east by a return flow in the upper water column 
to the south and east of Ritchie Hill. 
Egg abundances over the survey area during 
subsurveys 3 and 4 were calculated by using the 
curved and straight trajectory assumptions (Table 
3). The ratios of the curved and straight abundances 
generally decreased with egg stage. This decrease 
was expected because the curved trajectory is nearer 
to vertical deeper in the water col- 
umn (where the younger eggs are) 
than shallower in the column 
(where the older eggs are). The 
curved and straight trajectories 
tended to be nearly parallel in 
shallower water. 
Because eggs were advecting 
into the southwestern corner of the 
survey area (region 1, Fig. 4C) by 
the time they reached stage 11, 
only stages <10 were used in the 
estimation of daily egg production. 
The criterion used for this cutoff 
stage was that all stages > the first 
stage to have >20% of their abun- 
dance in region 1 would be ex- 
cluded from the analysis. This cri- 
terion was reached at stage 11. 
Using the abundance data calcu- 
lated by assuming a curved net tra- 
jectory (Table 3), we estimated that 
egg production was N 0 = 10.9 x 10 9 
eggs/day (CV=0.46) and that the 
mortality-rate estimate was Z = 
0.70/day (CV=0.69) (Fig. 6; Table 
4). These calculations used the ex- 
tra strata at North Hill and in the 
southwest, and all stations in 
subsurveys 3 and 4 falling within 
these strata were considered to 
have been originally selected 
within them. The N 0 estimated by 
assuming a straight trajectory was 
8.0 x 10 9 eggs/day (CV=0.49) with 
Z = 0.56 (CV=0.88). In the remain- 
ing analyses, the N Q value calcu- 
lated by assuming a curved trajec- 
tory was used because this value 
was likely to be a better approxima- 
tion to the truth than that obtained 
by assuming a straight trajectory. 
Daily fecundity of females 
A 
\ — 
1 \ 
1 
1 
j 
— 
/ 1 
/ 
1 — 
1( 
H 
1 — 
16 
1 
y 
\ | 
\ 
9 
\ 
\ 
\ 
\ 
\ 
\ 
B C 
16 
15 
14 
13 
s, 12 
03 
<55 11 
10 
9 
8 
<7 
Figure 4 
Studies of egg-stage distributions derived from subsurveys 3 and 4. (A) The posi- 
tions of centroids of the egg stages and the 36 subareas of the plankton survey 
area (solid lines) used in calculating centroid positions (Appendix 2). Centroid 7 
represents the combined stage group 1-7, and centroid 16 represents stages 16 
to 29 (hatching). The stratum boundaries of the survey area (dotted lines, slightly 
offset) are shown for reference. (B) Six regions and stations used in the distribu- 
tion analysis (region 3 comprised the inner and middle strata of the survey area), 
including the extra stations allocated in the southwestern corner. These latter 
stations were assumed to lie within region 1 for this analysis. (C) Proportions 
(circle areas) of eggs within the regions in B, by egg stage. 
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1 2 3 4 5 6 
Region 
The proportions of females in each 
ovarian stage in each DFRM trawl 
(Fig. 7) showed that the female 
population was, at first, nearly all 
in the prespawning state (stage 3). 
Maxima of hydrated, ovulated, and 
