Zischke and Griffiths: Stock assessment of Acanthocybium solandn in the Pacific Ocean 
409 
145°E 150°E 155°E 160°E 165°E 170°E 175°E 
Figure 1 
Map of the southwest Pacific Ocean with the exclusive economic zones 
of Australia (including Lord Howe and Norfolk islands) and New Cale- 
donia indicated by the solid lines. Data for the per-recruit assessment 
were collected throughout these zones. 
ETBF, catch, effort, and CPUE (catch 
per unit of effort) data for wahoo has 
been recorded in commercial logbooks 
since 1996 (AFMA 3 ). Similarly, in the 
commercial pelagic longline fishery in 
New Caledonia, logbook data have been 
recorded since 1997 (SPC 6 ). 
In addition to catch and effort data 
in commercial longline fisheries, size 
composition data are available for most 
fisheries. For Australian fisheries, on- 
board scientific observers from the Aus- 
tralian Fisheries Management Author- 
ity have recorded size composition data 
for wahoo in the ETBF since 2002. No 
catch and effort data are available from 
recreational fisheries. However, limited 
size composition data from the recre- 
ational fishery off eastern Australia 
(EC Rec) are available from an on-site 
survey of this fishery in 2010 (Zischke 
et ah, 2012), as well as from a volun- 
teer tagging program since 1973 (DPI 7 ). 
Limited size composition data from 
commercial and recreational fisheries 
off eastern Australia also are available 
from biological research conducted be- 
tween 2008 and 2011 (Zischke et ah, 
2013a; 2013b). To supplement data 
from Australian fisheries, size composi- 
tion data were obtained from observers 
and port samplers in the fishery in New 
Caledonia (SPC 6 ). 
Size composition data from all fisher- 
ies were restricted to the period 2008- 
2010 for all analyses because biological 
data were collected during this period. Age distribu- 
tions were calculated by converting fork length (FL) to 
age with a von Bertalanffy growth function reported 
by Zischke et al., 2013b (Table 1), who noted that age 
could not be calculated for any fish with an FL greater 
than the maximum theoretical fork length (L„) because 
such a fish would be assigned an infinite age. 
Estimation of mortality 
Natural mortality is a key component of fish stock 
dynamics because it directly influences the productiv- 
ity of a stock and the optimum fishery yield that can 
be obtained. One of the most reliable methods for es- 
timating the natural mortality of a stock is through 
mark-recapture experiments (Vetter, 1988). However, 
such experiments are expensive to implement and re- 
6 SPC (Secretariat of the Pacific Community). 2011. Un- 
publ. data [Commercial fisheries logbook data.] SPC, 
98848 Noumea, New Caledonia. 
7 DPI (Department of Primary Industries). 2011. Unpubl. 
data [Gamefish Tagging Program tagging data.] New 
South Wales DPI, Port Stephens, 2316, Australia. 
quire extensive fishing effort to ensure high numbers 
of initial marking and adequate recaptures for analy- 
sis. Mark-recapture work was outside the scope of this 
study; therefore, 2 empirical equations were used to 
provide estimates of natural mortality (M) of wahoo in 
the southwest Pacific Ocean. 
The first model was that of Pauly (1980): 
LogM = -0.0066 -0.2791ogL 00 + 0.65431ogA 
+ 0.46341ogT, (1) 
where and K - von Bertalanffy growth parame- 
ters (Table 1), respectively (Zischke et al., 
2013b); and 
T = the mean sea-surface temperature off east- 
ern Australia at 22.9°C (CSIRO 8 ). 
The second model used to estimate M was that of Hoe- 
nig (1983): 
8 CSIRO (Commonwealth Scientific and Industrial Research 
Organisation). 2012. Unpubl. data. [Sea-surface temper- 
ature data.] CSIRO, Dickson ACT 2602, Australia. 
