Zeldis et al.: An estimate of biomass of Hoplostethus atlanticus 
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Figure 1 
Map of New Zealand and location of spawning grounds (ovals) of orange roughy, Hoplostethus 
atlanticus. Also shown are the areas (2A, 3B, and 3A) of the east coast stock. 
Unlike sampling for the AEPM, sampling for the 
DFRM did not need to cover the entire spawning sea- 
son, allowing an estimate of spawning female bio- 
mass on Ritchie Bank to be produced from the por- 
tion of the voyage that did not suffer from ship and 
equipment breakdowns and that provided adequate 
data on planktonic egg production and fecundity. The 
DFRM was used to estimate the biomass of spawn- 
ing females by dividing the daily planktonic egg pro- 
duction in the survey area (eggs/day) by the daily 
fecundity of females (eggs/(kg x day). The biomass of 
spawning females was scaled by the maturity ogive, 
sex ratio, and spawning proportion to estimate the re- 
cruited biomass (>32 cm standard length) of orange 
roughy in the stock (where the stock is defined as those 
fish assumed to spawn on Ritchie Bank). The latter 
data were taken from a wide-area trawl survey in 
March-April 1993 (Tangaroa voyage TAN9303; Field 
et al. 2 ), that covered the area inhabited by the stock 
(Banks Peninsula to East Cape, Fig. 1). 
2 Field, K. D., R. I. C. C. Francis, J. R. Zeldis, and J. H. 
Annala. 1994. Assessment of the Cape Runaway to Banks 
Peninsula (ORH 2A, 2B, and 3 A) orange roughy fishery for the 
1994-95 fishing year. MAF Fisheries, Fisheries Assessment 
Research Document 94/20. NIWA, Greta Point, Wellington, New 
Zealand, 24 p. 
A necessary biological prerequisite for using the 
DFRM is that the target species has determinate 
annual fecundity ( Hunter and Lo, 1993). This enables 
total seasonal fecundity to be determined before fi- 
nal maturation so that the fecundity reduction rate 
can be monitored through the spawning season ( Lo 
et al., 1993). Orange roughy have determinate an- 
nual fecundity (Pankhurst et al., 1987; Bell et al., 
1992; Zeldis, 1993). Application of egg production 
methods to orange roughy also is possible, but only 
if the age of planktonic eggs at morphological stage 
can be estimated. Ageing of eggs was achieved by 
developing a model for ageing the eggs as they tra- 
versed the thermal gradient in the water column 
(Zeldis et al., 1995) and by describing the morpho- 
logical stages of the eggs (Grimes et al. 3 ). 
DFRM model 
To calculate the biomass of Ritchie Bank spawning 
females, the daily planktonic egg production in the 
3 Grimes, P. J., A. C. Hart, and J. R. Zeldis. 1997. Embryology 
and early larval development of orange roughy ( Hoplostethus 
atlanticus Collett). Unpubl. data. 
