407 NOAA First U.S. Commissioner National Marine Fishery Bulletin established 1881 of Fisheries and founder Fisheries Service of Fishery Bulletin Abstract—A stock assessment incor- Per-recruit stock assessment of wahoo porating sensitivity in biological pa- rameters and potential fishery man- (Acanthocybium solandri) in the agement strategies for wahoo (Acan- thocybium solandri) in the south- southwest Pacific Ocean west Pacific Ocean was undertaken to assess the stock status of this Mitchell T. Zischke (contact author)1,2 species for 2008–2010. Selectivity Shane P. Griffiths2 probabilities at age were similar for 2 commercial longline fisheries and a recreational sport fishery. How- Email address for contact author: [email protected] ever, the median exploited length and age were slightly higher in the 1 School of Biological Sciences commercial fisheries than in the The University of Queensland recreational fishery. Current fishing Brisbane, Queensland 4072, Australia mortality (Fcurrent) was predicted to Present address: Purdue University be lower than limit and target refer- Department of Forestry and Natural Resources ence points, with the exception that 195 Marsteller St Fcurrent exceeded the target refer- West Lafayette, Indiana 47907, United States ence point FSSB40 (fishing mortality 2 Oceans and Atmosphere Flagship at which the spawning stock biomass Commonwealth Scientific and Industrial Research Organisation per recruit [SSB/R] is 40% of the GPO Box 2583 SSB/R at F=0). This result indicates Dutton Park, Queensland 4102, Australia that wahoo may be at a greater risk of recruitment overfishing than of growth overfishing. Of the fishery management scenarios tested, intro- duction of a slot limit in the recre- ational fishery had the greatest ef- fect on assessment results; however, this effect was relatively minor and Wahoo (Acanthocybium solandri) is ern Pacific Ocean (Zischke, 2012). may not be practical to implement. a pelagic scombrid with a tropical Although catch and effort data from Given the relatively short life span and subtropical distribution in oce- subsistence, artisanal, and recre- of wahoo, ongoing biological monitor- anic waters worldwide (Collette and ational fisheries are scarce, evidence ing and rigorous collection of catch Nauen, 1983). This species is caught indicates that the recreational catch and effort data may facilitate contin- incidentally and retained as a by- of wahoo may exceed the commercial ued assessment of this species in the product in commercial pelagic long- catch off eastern Australia (Zischke southwest Pacific Ocean. line, purse-seine, and trolling fisher- et al., 2012), as has been reported for ies that target tunas and mackerels the Atlantic Ocean (SAFMC1). (Scombridae), broadbill swordfish Off eastern Australia, wahoo are (Xiphias gladius), and dolphinfishes retained as byproduct in the Com- (Coryphaena spp.) (Zischke, 2012). monwealth-managed Eastern Tuna The average annual global catch and Billfish Fishery (ETBF). The of wahoo in these fisheries has re- ETBF is a pelagic longline fishery mained around 3000 metric tons (t) with a quota on species that include since 1996 (Global Production Sta- albacore (Thunnus alalunga), yel- tistics 1950–2012, FAO, available lowfin tuna (T. albacares) and bigeye at website, accessed October 2012). tuna (T. obesus), as well as broadbill Manuscript submitted 20 March 2014. Commercial catches in the Pacific Manuscript accepted 21 July 2015. Ocean have increased 10-fold over 1 Fish. Bull. 113:407–418 (2015) the past 15 years (Global Production SAFMC (South Atlantic Fishery Man- agement Council). 2003. Fishery Online publication date: 10 August 2015. Statistics 1950–2012, FAO) because doi: 10.7755/FB.113.4.4 management plan for the dolphin and of increases in effort in tuna fisheries wahoo fishery of the Atlantic includ- in this region. Wahoo is also an im- ing a final environmental impact state- The views and opinions expressed or ment, regulatory impact review, initial implied in this article are those of the portant target and nontarget species in subsistence and artisanal fisher- regulatory flexibility analysis, and so- author (or authors) and do not necessarily cial impact assessment/fishery impact reflect the position of the National ies, as well as a prized catch in recre- statement, 308 p. SAFMC, Charleston, Marine Fisheries Service, NOAA. ational fisheries throughout the west- SC. [Available at website]. 408 Fishery Bulletin 113(4) swordfish and striped marlin (Kajikia audax) (AFMA2). (SAFMC1). In the waters off Taiwan, an age-structured The mean annual catch of wahoo in the ETBF has been model was used in 2007 to assess the current fishing 20.1 t (standard error [SE] 2.7) over the last 15 years, mortality (Fcurrent) against the reference points of 1) and the majority of catch has been derived from the fishing mortality at which the slope of the yield-per- northeastern area of Australia’s Exclusive Economic recruit (Y/R) curve is 10% of the slope at the origin 3 Zone (EEZ) (AFMA ). Apart from an arbitrary com- (F0.1) and 2) the fishing mortality at which the spawn- bined possession limit for wahoo, butterfly mackerel ing stock biomass per recruit (SSB/R) is 40% of the (Gasterochisma melampus) and slender tuna (Allot- SSB/R at F=0 (FSSB40) obtained from a Y/R model, and hunnus fallai) of 20 fish per trip (AFMA2), no species- results from that model indicated that wahoo were be- specific assessment or management framework exists ing fished at sustainable levels (Lee, 2008). for wahoo in this fishery. Wahoo also are caught in low Despite exploitation by multiple fishing sectors and quantities (<5 t annually) in state-managed trolling an increasing commercial catch in the southwest Pa- fisheries that target narrow-barred Spanish mackerel cific Ocean, no stock assessment has been completed (Scomberomorus commerson) in Queensland and New for wahoo in this region. Recent research has provid- South Wales (DAF4; DPI5). ed comprehensive information on the stock structure, Elsewhere in the southwest Pacific Ocean, wahoo age, growth, and reproductive biology of this species are retained as byproduct in the commercial pelagic in this region (Zischke et al., 2013a; 2013b; 2013c). longline fishery of New Caledonia, which targets spe- Wahoo grow quickly and reach sexual maturity at less cies similar to those targeted by the ETBF. Catch of than 1 year old (Zischke et al., 2013a; 2013b). Most wahoo in this fishery is similar to the ETBF, with a wahoo in fisheries catches, and their populations in mean annual catch of 25.1 t (SE 3.5) since 1997. No general, are 1–2 years old. Biological data, in conjunc- management measures exist for wahoo in this fishery. tion with fishery data from Australia and New Cale- Specialized recreational fisheries exist for wahoo off donia, were used to conduct the first stock assessment eastern Australia, and, although total catch is poorly for wahoo in the southwest Pacific Ocean, and we understood, recent evidence indicates that it may be present the results here. The objectives of the present equal to or exceed the total commercial catch in some study were 1) to apply an age-structured per-recruit regions (Zischke et al., 2012). Management measures model to the wahoo stock, 2) to examine the sensitiv- for recreational fisheries differ by state: a minimum ity of the population status derived by a per-recruit legal length of 75 cm in total length (TL) and a pos- model after incorporating variability in biological pa- session limit of 2 fish per person has been mandated rameters, and 3) to investigate potential management in Queensland (according to the Queensland Fisher- strategies for ensuring the long-term sustainability of ies Regulation 2008) but there is no minimum legal wahoo in this region. 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). Materials and methods Wahoo are low priority as a commercial species, a status that is likely to be responsible for the lack of Study area biological research on the species that has hindered the undertaking of rigorous stock assessments (Zischke, The global stock structure of wahoo is uncertain. Al- 2012). However, preliminary stock assessments have though the species is reputed to exist as a single pan- been completed for wahoo in the Atlantic Ocean and mictic population worldwide (Theisen et al., 2008), re- the waters off Taiwan. The Atlantic assessment in 2000 cent evidence suggests that wahoo may exist as mul- considered wahoo in the subtropical western North At- tiple phenotypic populations throughout the Pacific lantic, Caribbean, and Gulf of Mexico to be a single Ocean (Zischke et al., 2013c). A fine-scale, spatially stock and used median annual catch as a proxy for explicit analysis of morphometrics and parasites has fishing mortality (F) to indicate a maximum sustain- indicated that wahoo off eastern Australia form part of able yield (MSY) of 640–740 t, but an assessment of a single stock in the southwest Pacific Ocean (Zischke the current status of the stock was not undertaken et al., 2013c). Because the geographic extent of this stock has not been resolved, we have adopted a precau- 2 AFMA (Australian Fisheries Management Authority). 2011. tionary approach, defining the stock for assessment as Eastern Tuna and Billfish Fishery (ETBF) management ar- consisting of wahoo from the EEZ off eastern Australia rangements booklet: 2011 fishing season, 31 p. AFMA, Can- and the EEZ of New Caledonia (Fig. 1). berra, Australia. [Available at website]. 3 AFMA (Australian Fisheries Management Authority). 2011. Unpubl. data. [Eastern Tuna and Billfish Fishery commer- Fishery data used for stock assessment cial logbook data.] AFMA, Canberra, 2610, Australia. 4 DAF (Department of Agriculture and Fisheries). 2011. Un- Limited catch and effort data are available for wahoo publ. data. [Queensland commercial and charter fisheries in the southwest Pacific Ocean because wahoo are not logbook data.] Queensland DAF, Brisbane, 4001, Australia.