99 
Estimating the annual proportion of 
nonspawning adults in New Zealand 
hoki, Macruronus novaezelandiae 
Mary E. Livingston 
Marianne Vignaux 
Kathy A. Schofield 
National Institute of Water and Atmospheric Research 
RO Box 14-901 Kilbirnie, Wellington, New Zealand 
E-mail address: m.livingston@niwa.cri.nz 
Abstract .—Trawl surveys of hoki, 
Macruronus novaezelandiae (Hector) in 
the Southland and subantarctic areas 
(Southern Plateau) of New Zealand’s 
Exclusive Economic Zone were carried 
out in May 1992 and 1993. The propor- 
tion of females of each age that would 
spawn in the coming spawning season 
(July-August) was estimated on the ba- 
sis of histological analysis of gonad 
samples and ageing data. Comparisons 
were made between numbers of fish at 
age in these surveys and numbers of 
fish at age in surveys in November-De- 
cember 1991 and 1992 to estimate mi- 
gration before May. 
The results indicate that 66% (stan- 
dard error [SE] of 3%) of females age 7 
and over that were on the Southern 
Plateau in May 1992 would spawn in 
winter 1992, compared with 65% (SE 
2%) in 1993. If the number of hoki esti- 
mated to have already migrated out of 
the survey area in May are included as 
prespawners, then up to 67% (SE 5%) 
of adult females were predicted to 
spawn in winter 1992 and 82% (SE 3%) 
in winter 1993. 
This study confirms that the propor- 
tion of adult hoki that spawn in a given 
year is substantially less than 1. It is 
not known how much this varies, 
whether it is with or without trend, or 
whether it is correlated with any envi- 
ronmental variables. Fishery indicators 
such as stock and fishery risk are par- 
ticularly sensitive to the annual propor- 
tion of adult hoki that spawn, and it 
is possible that its variation could ob- 
scure any underlying stock-recruitment 
relationship. 
Manuscript accepted 4 September 1996. 
Fishery Bulletin 95:99-113 (1997). 
Hoki ( Macruronus novaezelandiae 
Hector) form New Zealand’s largest 
commercial fishery with an annual 
catch of about 200,000 metric tons 
(t). The fish are widely distributed 
throughout New Zealand’s 200-mile 
Exclusive Economic Zone in depths 
of 50-800 m, but most commercial 
fishing is at depths of 200-800 m 
around the South Island (Fig. 1). 
Fishing effort is greatest during the 
July-August spawning season off 
the west coast and in Cook Strait 
but also occurs on the Chatham Rise 
and management areas south of 
Puysegur Point (hereafter referred 
to as the Southern Plateau) (Fig. 1) 
throughout the rest of the year. 
Although managed as a single 
stock, hoki are assessed annually as 
two stocks (Sullivan and Cordue 1 ; 
Sullivan et al. 2 ). There is no genetic 
evidence for a split, but because 
morphometric and growth rate dif- 
ferences have been found between 
the two spawning grounds (Horn 
and Sullivan, 1996; Livingston and 
Schofield, 1996), a cautious ap- 
proach in determining yield has 
been taken. Hoki are assessed as 
two stocks by using stock reduction 
models (Sullivan et al. 2 ). Abundance 
indices estimated from acoustic sur- 
veys, trawl surveys, and catch-per- 
unit-of-effort data on the spawning 
grounds have been the main inputs 
to the models (Sullivan et al. 2 ). 
Of the two stocks, the western 
stock, which resides primarily on 
the Southern Plateau and spawns 
off the west coast of the South Is- 
land, is substantially larger than 
the eastern stock, which resides 
primarily on the Chatham Rise and 
spawns in Cook Strait. Juvenile 
hoki (2-5 yr) of both stocks appear 
to reside and mix together on the 
Chatham Rise in relatively shallow 
water. As the fish reach maturity, 
it is assumed that they recruit to 
their respective stocks. 
Winter surveys of the Southern 
Plateau and Chatham Rise have 
shown that significant numbers of 
mature-size hoki, both males and 
females, do not partake in the 
spawning migration in a given year 
(Livingston et al., 1991; Hurst and 
Schofield, 1995). 
From trawl surveys of the South- 
ern Plateau in July-August and 
November-December 1990, it was 
estimated that the ratio of recruited 
1 Sullivan, K. J., and P. L. Cordue. 1992. 
Stock assessment of hoki 1992. New 
Zealand Fisheries Assessment Res. Docu- 
ment 92/12, NIWA Greta Point library, 
Wellington, New Zealand, 43 p. 
2 Sullivan, K. J., P. L. Cordue, and S. L. 
Ballara. 1995. A review of the 1992-93 
hoki fishery and assessment of hoki stocks 
for 1994. New Zealand Fisheries Assess- 
ment Research Document 95/5, NIWA 
Greta Point library, Wellington, New Zea- 
land, 45 p. 
