576 
Abstract .—The recruited biomass 
of orange roughy, Hoplostethus atlanti- 
cus, was estimated for the New Zealand 
mid-east coast orange roughy stock 
with the daily fecundity reduction 
method (DFRM). These fish migrate to 
Ritchie Bank and spawn between 850 
and 900 m for about one month in win- 
ter. The biomass of spawning females 
was estimated by dividing mean daily 
planktonic egg production, N 0 (eggs/ 
day), by mean daily fecundity, D (eggs/ 
kg per day). The stock biomass was 
then estimated by multiplying the 
spawning female biomass by the ratio 
of all recruited fish to females that 
would spawn that year, estimated with 
a wide-area trawl survey made over the 
stock area two months before the 
spawning season. 
The mean daily planktonic egg pro- 
duction was sampled near the peak of 
the spawning season, by using a strati- 
fied-random plankton survey. Eggs 
were staged and aged after accounting 
for their thermal history as they as- 
cended the water column. Because 
young eggs were damaged by the net 
and older eggs were affected by advec- 
tion out of the plankton survey area, 
relatively few egg stages were available 
for estimating N 0 ( 10.9 x 10 9 eggs/day), 
and the estimate was somewhat impre- 
cise (CV=0.46). Mean daily fecundity 
(787 eggs/(kg x day), CV=0.11) was es- 
timated from the daily rate of decline 
in population fecundity per mature fe- 
male weight (/?,). Fecundity per female 
weight was estimated from a trawl sur- 
vey made in the spawning area during 
the spawning season and was calcu- 
lated as the mature eggs/kg of active 
spawners multiplied by the proportion 
of active spawners in each trawl. 
Spawning female biomass was 14,000 t 
(CV=0.50), and stock biomass was 
26,000 t (CV=0.50). Mean daily fecun- 
dity was probably under-estimated be- 
cause spent fish appeared to migrate 
from the spawning area during the fe- 
cundity reduction measurement period 
and reduce stock biomass to about 
18,200 t. The DFRM biomass estimate 
was of central importance in the intro- 
duction of greatly reduced total allow- 
able catch levels in this fishery. 
Manuscript accepted 26 February 1997. 
Fishery Bulletin 95:576-597(1997). 
An estimate of orange roughy, 
Hoplostethus atlanticus, biomass using 
the daily fecundity reduction method 
John R. Zeldis* 
R. I. Chris Francis 
Malcolm R. Clark 
Jonathan K. V Ingerson 
Paul J. Grimes 
Marianne Vignaux 
National Institute of Water and Atmospheric Research (NIWA) 
RO. Box 14-901, Kilbirnie, Wellington, New Zealand 
*E-mail address: j.zeldis@niwa.cri.nz 
The orange roughy ( Hoplostethus 
atlanticus , Trachichthyidae) fishery 
on Ritchie Bank on the eastern New 
Zealand continental slope (Fig. 1) 
was the second largest orange 
roughy fishery in New Zealand dur- 
ing the late 1980’s and early 1990’s, 
with a total allowable commercial 
catch (TACC) of about 10,000 met- 
ric tons (t) per year. Trends in catch 
per unit of effort (CPUE) indicated 
that the stock size was diminishing 
rapidly under this management re- 
gime, although the stock reduction 
analysis for the fishery did not esti- 
mate stock size precisely (Field et 
al. 1 ). Experience with other major 
orange roughy fisheries in New 
Zealand (the “Box” fishery on north- 
ern Chatham Rise and the Chal- 
lenger Plateau fishery [Fig. 1; 
Clark, 1995]) indicated that over- 
fishing of the Ritchie Bank stock 
was likely because of low productiv- 
ity. However, without adequate 
knowledge of stock size, it was dif- 
ficult to set a TACC that would al- 
low a sustainable fishery. 
Zeldis ( 1993) concluded that both 
the annual egg-production method 
( AEPM; Saville, 1964; Picquelle and 
Megrey, 1993; Koslow et al., 1995) 
and the daily fecundity reduction 
method (DFRM; Lo et al., 1992; Lo 
et al., 1993) would be feasible for the 
estimation of absolute spawning 
biomass of orange roughy. A voyage 
was made to Ritchie Bank from 
early June to early July, 1993 
( Tangaroa voyage TAN9306), with 
the intention of using both types of 
egg-production survey method. 
With the AEPM, annual egg produc- 
tion is the sum of daily planktonic 
egg production estimates made over 
the entire spawning season from 
separate subsurveys. Unfortu- 
nately, the voyage failed to sample 
annual egg production for two rea- 
sons. First, although the voyage was 
executed as a series of five sub- 
surveys, two of the subsurveys were 
not completed because of ship and 
equipment breakdowns and be- 
cause of a lack of time at the end of 
the voyage. Second, the voyage pe- 
riod ended before spawning had fin- 
ished for the season, so that the 
annual egg production was not com- 
pletely sampled. 
1 Field, K. D., R. I. C. C. Francis, and J. H. 
Annala. 1993. Assessment of the Cape 
Runaway to Banks Peninsula (ORH 2A, 
2B, and 3A) orange roughy fishery for the 
1993-94 fishing year. MAF Fisheries, 
Fisheries Assessment Research Document 
93/8. NIWA, Greta Point, Wellington, New 
Zealand, 17 p. 
