Zeldis et al. : An estimate of biomass of Hoplostethus atlsnticus 
583 
B t -was determined from the standard error of 1,000 
estimates of B ^ , formed by dividing the 1,000 esti- 
mates of N q (Appendix 2) by 1,000 normally distrib- 
uted estimates of D, formed from the mean and stan- 
dard error of D. 
Proportions spawning, recruited, and female 
The scaling factors needed for converting the bio- 
mass estimate of Ritchie Bank spawning females to 
one for recruited fish (>32 cm SL for both sexes) for 
the entire mid-east coast stock were estimated from 
the March- April 1993 wide-area east coast trawl sur- 
vey (Field et al. 2 ), instead of from the trawl data gath- 
ered at the time of the egg survey, for two reasons. 
First, not all recruited fish spawn each year (and thus 
may not migrate to Ritchie Hill). Second, a more pre- 
cise estimate of sex ratio is available from the trawl 
survey than from the relatively few trawls carried 
out during spawning (when sex ratios are most vari- 
able; Zeldis, 1993). The trawls from the wide-area 
survey used for the scaling factors were those from 
over the entire mid-east coast survey area, from just 
north of Ritchie Bank, south to Banks Peninsula (Fig. 
1; quota management areas 2A South, 2B, and 3A, 
respectively). This is the likely distribution of the 
stock that migrates to the Ritchie Bank to spawn. 10 
No spawning orange roughy have been located in 
areas 2B or 3A, and genetic data show that orange 
roughy from these three areas cannot be separated, 
whereas they are genetically distinct from orange 
roughy on Chatham Rise (Fig. 1). 
Stage-3 (late vitellogenic) females in each trawl in 
the 1993 wide-area trawl survey were assumed to be 
those that would spawn that year (Bell et al., 1992). 
Because ovaries of stage-3 females are indistinguish- 
able macroscopically from ovaries of fish in which 
massive atresia has occurred (Bell et al., 1992), the 
macroscopic staging was checked by histological ex- 
amination of about 20 stage-3 fish collected on each 
day of the 28-day trawl survey. 
Recruited biomass 
The scalar (S) was calculated as 
10 Annala, J. H., and K. J. Sullivan (compilers). 1996. Report 
from the Fishery Assessment Plenary, April-May 1996: stock 
assessments and yield estimates, 308 p. Unpubl. report held 
in NIWA Library, Wellington, New Zealand. 
where P reci and P spfi 
Ci 
A 
l 
the proportions (by weight) 
of recruited fish and spawn- 
ing (stage-3) females, re- 
spectively, in the catch from 
the ith trawl; 
the catch rate (t/nmi) at the 
zth trawl; 
the stratum area for the 
stratum containing the ith 
trawl; and 
the number of trawls for the 
stratum containing the i th 
trawl. 
The precision of the estimates of S was estimated 
by using the following bootstrap procedure. For each 
trawl, the triplet (X, , P rec i , P sp fi ) was calculated, where 
X = CA i /n j . One thousand simulated data sets were 
generated by drawing triplets at random with re- 
placement. Each simulated survey contained the 
same number of trawls as the area of the original 
trawl survey. For each simulated survey a bootstrap 
estimate of S was calculated as 
X.'fV.A)’ 
The bootstrap estimates of S were used to calculate 
a CV for S. 
The recruited biomass, B , was calculated by us- 
ing the DFRM biomass model given above. The boot- 
strap estimates for S were combined with the boot- 
strap estimates of B t to obtain a CV for B rec . 
Results 
Daily planktonic egg production 
Planktonic eggs were first captured in very low num- 
bers on 15 June during subsurvey 1 (Fig. 3). Egg 
abundance remained low until the end of subsurvey 
2 (25 June). This subsurvey was prolonged by ship 
and sampling-equipment breakdowns, and only the 
central strata, two of the middle strata, and none of 
the outer strata were sampled. The breakdowns pre- 
vented further sampling until the start of subsurvey 
3 on 28 June, when large quantities of eggs were 
captured. Catches then decreased during subsurvey 
4 (ending 6 July). Sampling of subsurveys 3 and 4 
was completed. In subsurvey 5, only the central stra- 
tum and one middle stratum were occupied before 
the scheduled survey period ended on 7 July. Egg 
production continued at this time. 
