588 
Fishery Bulletin 95(3), 1997 
Table 3 
Abundances of eggs (x 10 -6 ) and coefficients of variation 
(CV) at stage, during DFRM planktonic egg survey, calcu- 
lated with curved and straight net trajectory assumptions. 
Also given are the ratios of curved and straight abundances. 
Stage 
Curved 
abund. 
CV 
Straight 
abund. 
CV 
Ratios 
<7 
7,036 
0.26 
5,453 
0.28 
1.29 
8 
487 
0.40 
424 
0.43 
1.15 
9 
673 
0.60 
451 
0.51 
1.49 
10 
316 
0.43 
276 
0.49 
1.15 
11 
400 
0.24 
351 
0.26 
1.14 
12 
1,420 
0.32 
1,276 
0.32 
1.11 
13 
740 
0.23 
716 
0.24 
1.03 
14 
276 
0.38 
260 
0.37 
1.06 
15 
34 
0.42 
38 
0.38 
0.90 
proportions of macroscopic stage-3 (vitellogenic) fish 
declined to 5% by the midpoint of the trawl survey 
period and to 0% by the end; stage-4 (hydrated) fish 
showed a similar decreasing trend. Thus no 
prespawning fish were present at the end of the trawl 
survey (13 July). 
Turnover during the trawl survey period may have 
biased the biomass estimate if prespawning fish ar- 
rived late to the trawl survey area (after trawling 
for R / had started), at the beginning of the season. 
This means that not all prespawning fish would have 
been sampled by trawls in the spawning area, which 
would cause an underestimate of R-, because fish that 
had started spawning would be over-represented. 
Similarly, if spent fish departed the trawl survey area 
early (before trawling for R t had ended) toward the 
end of the season, spent fish would be under-repre- 
sented by trawls in the spawning area. In this case, 
i? ; would be overestimated because fish which had 
not finished spawning would be over-represented. 
Both of these effects (late arrivals and early depar- 
tures) would cause an underestimate of D, which, in 
turn, would cause an overestimate of biomass, N Q /D. 
Was it likely that late arrivals or early departures 
(or both) of spawners occurred in the present study? 
The annual fecundity/kg of prespawners, estimated 
from fish sampled before the i? ; sampling period and 
before any eggs were caught in the plankton (Fig. 8), 
was 27, 271 eggs/(kg x yr). If this estimate is divided 
by the estimated daily fecundity/kg (787 eggs/(kg x 
day); Table 4), the period required for the average 
fish to spawn completely is 35 days. However, the 
time lag between the first appearance of significant 
proportions (>0.05) of ovulated and spent fish was 
about 19 days (from 14 June to 2 July; Fig. 7). If this 
Table 4 
Parameter estimates for DFRM for Ritchie Hill spawning 
female biomass and mid-east coast recruited biomass, 
June-July 1993 (with coefficients of variation in paren- 
theses). N 0 = daily egg production for Ritchie Hill survey 
area (estimated with curved net trajectory); D = weight 
specific daily fecundity of females; B sp ^ = biomass of spawn- 
ing females in Ritchie Hill survey area; S = ratio of re- 
cruited biomass to that of spawning females; B = biom- 
ass of recruited fish. Parameter estimates with subscripts 
marked “ turn ” have turnover incorporated (see text); CV’s 
were not estimated in these cases. 
Parameter 
Estimate 
D 
B 
S 
B i 
D 
spf 
J spf turn 
rec,turn 
10.9 x 10 9 eggs/day (0.46) 
787 eggs/(kg x day) (0.11) 
14.000 t (0.50) 
1.85 (0.03) 
26.000 (0.50) 
1,106 eggs/( kg x day) 
9,900 t 
18,200 t 
Table 5 
Mean abundances (per m 2 ) of all eggs < stage 7 and dates 
of sampling in the central strata for each subsurvey. 
Subsurvey 
Date 
Mean 
CV 
1 
15-17 June 
0.0 
0.0 
2 
20-25 June 
3.9 
0.34 
3 
29 June-1 July 
49.0 
0.29 
4 
3-5 July 
22.6 
0.46 
5 
6-7 July 
22.2 
0.50 
4 and 5 
3-7 July 
22.4 
0.34 
lag is interpreted as the duration of spawning in in- 
dividual fish, D was underestimated by the fecun- 
dity reduction trawling. 
It would appear, however, that late arrival of 
prespawners to the trawling area did not contribute 
greatly to the underestimation of D. The R t sampling 
period began on 20 June when prespawner (stage-3) 
proportions had become low (0.20; Fig. 7) and were 
decreasing rapidly. At this time the estimated R t was 
only about 10% below the prespawning level (Fig. 
8). Eggs first appeared in the plankton on 15 June, 
but catches of young eggs in the central strata were 
still relatively small (3.9 eggs/m 2 ; Table 5) during 
20-25 June (subsurvey 2). Therefore, only a relatively 
small reduction in R t would have been expected by 
