408 
Fishery Bulletin 113(4) 
swordfish and striped marlin (Kajikia audax) (AFMA 2 ). 
The mean annual catch of wahoo in the ETBF has been 
20.1 t (standard error [SE] 2.7) over the last 15 years, 
and the majority of catch has been derived from the 
northeastern area of Australia’s Exclusive Economic 
Zone (EEZ) (AFMA 3 ). Apart from an arbitrary com- 
bined possession limit for wahoo, butterfly mackerel 
(Gasterochisma melampus) and slender tuna (Allot- 
hunnus fallai) of 20 fish per trip (AFMA 2 ), no species- 
specific assessment or management framework exists 
for wahoo in this fishery. Wahoo also are caught in low 
quantities (<5 t annually) in state-managed trolling 
fisheries that target narrow-barred Spanish mackerel 
(Scombej'omorus commerson ) in Queensland and New 
South Wales (DAF 4 ; DPI 5 ). 
Elsewhere in the southwest Pacific Ocean, wahoo 
are retained as byproduct in the commercial pelagic 
longline fishery of New Caledonia, which targets spe- 
cies similar to those targeted by the ETBF. Catch of 
wahoo in this fishery is similar to the ETBF, with a 
mean annual catch of 25.1 t. (SE 3.5) since 1997. No 
management measures exist for wahoo in this fishery. 
Specialized recreational fisheries exist for wahoo off 
eastern Australia, and, although total catch is poorly 
understood, recent evidence indicates that it may be 
equal to or exceed the total commercial catch in some 
regions (Zischke et al., 2012). Management measures 
for recreational fisheries differ by state: a minimum 
legal length of 75 cm in total length (TL) and a pos- 
session limit of 2 fish per person has been mandated 
in Queensland (according to the Queensland Fisher- 
ies Regulation 2008) but there is no minimum legal 
length and a possession limit of 5 fish per person in 
New South Wales (according to the New South Wales 
Fisheries Management [General] Regulation 2010). 
Wahoo are low priority as a commercial species, a 
status that is likely to be responsible for the lack of 
biological research on the species that has hindered the 
undertaking of rigorous stock assessments (Zischke, 
2012). However, preliminary stock assessments have 
been completed for wahoo in the Atlantic Ocean and 
the waters off Taiwan. The Atlantic assessment in 2000 
considered wahoo in the subtropical western North At- 
lantic, Caribbean, and Gulf of Mexico to be a single 
stock and used median annual catch as a proxy for 
fishing mortality (F) to indicate a maximum sustain- 
able yield (MSY) of 640-740 t, but an assessment of 
the current status of the stock was not undertaken 
2 AFMA (Australian Fisheries Management Authority). 2011. 
Eastern Tuna and Billfish Fishery (ETBF) management ar- 
rangements booklet: 2011 fishing season, 31 p. AFMA, Can- 
berra, Australia. [Available at website]. 
3 AFMA (Australian Fisheries Management Authority). 2011. 
Unpubl. data. [Eastern Tuna and Billfish Fishery commer- 
cial logbook data.] AFMA, Canberra, 2610, Australia. 
4 DAF (Department of Agriculture and Fisheries). 2011. Un- 
publ. data. [Queensland commercial and charter fisheries 
logbook data.] Queensland DAF, Brisbane, 4001, Australia. 
5 DPI (Department of Primary Industries). 2011. Unpubl. 
data. [New South Wales commercial fisheries logbook data.] 
New South Wales DPI, Port Stephens, 2316, Australia. 
(SAFMC 1 ). In the waters off Taiwan, an age-structured 
model was used in 2007 to assess the current fishing 
mortality (F current ) against the reference points of 1) 
fishing mortality at which the slope of the yield-per- 
recruit (Y/R) curve is 10% of the slope at the origin 
(Fq.i) and 2) the fishing mortality at which the spawn- 
ing stock biomass per recruit (SSB/R) is 40% of the 
SSB/R at F= 0 (FssB4o) obtained from a Y/R model, and 
results from that model indicated that wahoo were be- 
ing fished at sustainable levels (Lee, 2008). 
Despite exploitation by multiple fishing sectors and 
an increasing commercial catch in the southwest Pa- 
cific Ocean, no stock assessment has been completed 
for wahoo in this region. Recent research has provid- 
ed comprehensive information on the stock structure, 
age, growth, and reproductive biology of this species 
in this region (Zischke et al., 2013a; 2013b; 2013c). 
Wahoo grow quickly and reach sexual maturity at less 
than 1 year old (Zischke et al., 2013a; 2013b). Most 
wahoo in fisheries catches, and their populations in 
general, are 1-2 years old. Biological data, in conjunc- 
tion with fishery data from Australia and New Cale- 
donia, were used to conduct the first stock assessment 
for wahoo in the southwest Pacific Ocean, and we 
present the results here. The objectives of the present 
study were 1) to apply an age-structured per-recruit 
model to the wahoo stock, 2) to examine the sensitiv- 
ity of the population status derived by a per-recruit 
model after incorporating variability in biological pa- 
rameters, and 3) to investigate potential management 
strategies for ensuring the long-term sustainability of 
wahoo in this region. 
Materials and methods 
Study area 
The global stock structure of wahoo is uncertain. Al- 
though the species is reputed to exist as a single pan- 
mictic population worldwide (Theisen et al., 2008), re- 
cent evidence suggests that wahoo may exist as mul- 
tiple phenotypic populations throughout the Pacific 
Ocean (Zischke et al., 2013c). A fine-scale, spatially 
explicit analysis of morphometries and parasites has 
indicated that wahoo off eastern Australia form part of 
a single stock in the southwest Pacific Ocean (Zischke 
et al., 2013c). Because the geographic extent of this 
stock has not been resolved, we have adopted a precau- 
tionary approach, defining the stock for assessment as 
consisting of wahoo from the EEZ off eastern Australia 
and the EEZ of New Caledonia (Fig. 1). 
Fishery data used for stock assessment 
Limited catch and effort data are available for wahoo 
in the southwest Pacific Ocean because wahoo are not 
targeted in any commercial fisheries and are taken 
as part of the specialized recreational sport fishery in 
this region (Zischke, 2012; Zischke et al., 2012). In the 
