southern and western tuna and billfish...

Southern and Western Tuna and Billfish Fishery 71

Southern and WesternTuna and Billfish Fishery

Main featuresS T A T U S

Bigeye tuna not overfished; yellowfin tuna and broadbill swordfish uncertain;overfishing of bigeye tuna is occurring inthe broader Indian Ocean

R E L I A B I L I T Y O F T H E A S S E S S M E N T

Stock-status indicators are rudimentary; norigorous assessment of swordfish in theIndian Ocean has been undertaken;unreliable for the AFZ, because interactionswith broader regional stocks are uncertain

C U R R E N T L O N G L I N E C A T C H

2002 2003

swordfish 1998 t (A$21.3m) 1184 t (A$10.2m)

bigeye 418 t (A$5.6m) 205 t (A$2.5m)

yellowfin 354 t (A$3.2m) 191 t (A$1.7m)

L O N G - T E R M P O T E N T I A L Y I E L D

Uncertain; Japanese AFZ longline catchesof tuna and billfish peaked in 1984 at2219 t (including 1052 t of yellowfin);domestic catches have exceeded 3000 t inrecent years

M A I N M A N A G E M E N T O B J E C T I V E

Control of total catch of target species,adjusted as stock dynamics become betterunderstood

M A N A G E M E N T M E T H O D S

Input controls, including limited entry; gearand area restrictions; and bycatchrestrictions. Output controls by individualtransferable quotas planned for 2005

72 Fishery Status Reports | 2 0 0 4 |

Highlights

• The Southern and Western Tuna and Billfish Fisherydeveloped rapidly after exclusion of Japaneselongliners from the Australian Fishing Zone (AFZ),with hook sets increasing more than ten-fold, andthe total catch increasing six-fold.

• Catch levels began to decline in 2003 when lowprices and higher operating costs reduced fishingactivity.

• The longline fishery targets broadbill swordfish,bigeye tuna and yellowfin tuna, with most of thecatch exported fresh-chilled to markets in Japan andthe United States.

• Domestic management—to involve total allowablecatches and individual transferable quotas—mustaccommodate international arrangements expectedto be established by the Indian Ocean TunaCommission.

• About 1.3 million tonnes of tuna and billfish arecaught in the Indian Ocean each year, with abouthalf taken by industrial longline and purse-seinefleets.

• Region-wide management action is requiredbecause current catch levels of bigeye, yellowfin and swordfish are unlikely to be sustainable in thelong term.

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Southern and Western Tuna

and Billfish Fishery (2003)

Relative fishing intensity

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Limit ofAustralianFishing Zone


Background

History of the fishery

The Southern and Western Tuna and BillfishFishery (SWTBF) extends from 141ºE (theSouth Australia–Victoria border) aroundwestern and northern Australia to Cape York inQueensland. However, the commerciallyvaluable tuna and billfish species are rare in theshallow northern region of the AustralianFishing Zone (AFZ), so fishing activities areconcentrated in oceanic waters along thewestern and southern coasts. The western andsouthern areas, separated at 34˚S, are managedas one fishery, although permits are issued toaccess either one or both areas.

An intensive surface fishery for southernbluefin tuna (Thunnus maccoyii) developed offSouth Australia in the 1950s, and also operatedin the Albany–Esperance area between 1970and 1988, using trolling, bait-and-pole and (offSouth Australia) purse-seine techniques.Otherwise, domestic tuna-fishing activity offWestern Australia had been limited toopportunistic handline operations from localtrawl and rock-lobster vessels, and trolling byrecreational gamefishers.

Historically, the main SWTBF catch wastaken by Japanese pelagic longliners operatingin the AFZ under bilateral agreements. Theytargeted high-value bigeye tuna (Thunnusobesus) in the southwest, and yellowfin tuna (T.albacares) and striped marlin (Tetrapturusaudax) in the northwest. Those longliners havebeen excluded from Australian waters sinceNovember 1997. A domestic longline fisheryhas replaced them, using monofilamentmainline gear and concentrating on broadbillswordfish (Xiphius gladius), in addition tobigeye and yellowfin. Incidental catches ofalbacore tuna (T. alalunga), longtail tuna (T.tonggol) and southern bluefin are also made. Inthe South Australian area, where the surfacefishery for southern bluefin operates, skipjacktuna (Katsuwonus pelamis) is an occasionallate-season (March–April) target of purse-seiners (a separate Status Reports chapter isdevoted to skipjack).

The SWTBF is contiguous with larger tunaand billfish fisheries within Indonesia’sExclusive Economic Zone and elsewhere in theIndian Ocean. Australia is a member of theIndian Ocean Tuna Commission (IOTC), amultilateral organisation with 18 members,established under the United NationsConvention on the Law of the Sea. The IOTCprovides a mechanism for encouragingparticipants in Indian Ocean tuna fisheries tocomply with international conservation andmanagement measures. It also provides a forumfor stock assessment and regional managementof the tuna and billfish of the Indian Ocean.

Interest in the SWTBF increasedsignificantly in 1998, with a considerableincrease in investment and in prices paid forthe transfer of fishing permits. About20 vessels operated, 8 of which caught over 35 t each. In previous years there were few ifany dedicated SWTBF domestic longlinevessels, and most longliners were Japanese.However, in 1998 a number of larger vesselswere renovated extensively for longlining, andtwo new ones were built.

Western Australia has a keen recreationalgame fishery, targeting sailfish (Istiophorusplatypterus), black marlin (Makaira indica),blue marlin (M. mazara), striped marlin andyellowfin. Consideration of recreational fishinginterests in the late 1980s had resulted in theprohibition of Japanese longlining within 50n.mile of the Western Australian coast. It alsoled to Japanese agreement that billfish otherthan swordfish would not be targeted, and thatall black and blue marlin taken alive would bereleased. In 1994 Western Australia passedlegislation preventing the landing of all billfishof the family Istiophoridae. However, thislegislation was not enforced until December1999. Meanwhile, in 1998 the Commonwealthbanned the retention of blue and black marlin,whether alive or dead, taken anywhere in theAFZ by commercial fishing.

The Australian Fisheries ManagementAuthority (AFMA) has agreed that, when amanagement plan for the SWTBF isimplemented, the demarcation at 34°S betweenthe southern and western components of the


fishery would be removed to further theintegration of tuna fisheries in Australia.Currently, there are 124 concessions foroperation in the SWTBF: 72 allow access toboth the southern and western components, 45allow access to the southern component only,and 7 to the western component only. Theconcessions are a mix of pelagic-longlineentitlements, minor-line entitlements, purse-seine entitlements and poling entitlements.Unification of the southern and westerncomponents could possibly increase fishingeffort in both areas.

Most Australian longliners operating in theSWTBF are 15–30 m long and deploymonofilament longline gear. They store theircatch on ice, in ice slurry or in brine-spraysystems. Trips are generally of 3–10 days, withabout 1000 hooks deployed before sunrise eachday. During 2001, however, daytime-settingsouth of 30˚S was restricted to minimiseinteractions with seabirds. The longliners thattarget swordfish make shallow (20–120 m) setsat night, using squid baits and chemical lightsticks. Most longlining activity is within theAFZ, but some extends beyond it. The rangeoffshore is limited for most vessels by theirsmall size and lack of freezer facilities. In thewest, most of the catch is landed at Fremantle,Geraldton and Carnarvon, while most of thesouthern landings are made at Albany and PortLincoln. The distances between some fishinggrounds and ports have resulted in longer trips(of up to fourteen days).

AFMA permitted some domestic longliningin the Christmas Island and Cocos (Keeling)Islands regions of the AFZ under a controlled-fishing program. There has been very littleactivity, probably because of the remoteness ofthe islands from the Australian mainland,limited support facilities and difficulties intransporting fresh product to overseas markets.In the past, Japanese longliners have takengood catches of bigeye and yellowfin there, anddomestic activity around the islands is expectedas the SWTBF develops. The existence ofendangered seabirds endemic to the region willrequire appropriate controls on fishingpractices.

Japan began pelagic longlining off Australiain the 1950s. The large (40–55 m) freezerlongliners remained at sea for two to threemonths, deploying 2500–3500 hooks each dayon 60 n.mile multi-strand mainlines. The fleet’sannual catch ranged up to 125 t of swordfish,1034 t of bigeye and 1052 t of yellowfin. Afterimplementation of the AFZ in 1979, Japaneseactivity in the zone was licensed under bilateralagreements. Australia progressively restrictedareas of access until Japan’s longliners weretotally excluded in November 1997.

The IOTC vessel registry for the IndianOcean identifies almost 1800 individual tunavessels of length greater than 24 m, flying 33different flags. Gear types include longline,purse-seine, gillnet and pole-and-line. Thenumber of artisanal tuna vessels, fishingpredominantly in the Exclusive EconomicZones of Indian Ocean coastal states, is in thetens of thousands. In general, the artisanalvessels have a very limited range, no freezercapacity and limited storage. Their catch istypically sold at local markets.

Many longliners from Japan, Republic ofKorea and Taiwan fish High Seas areas acrossthe Indian Ocean, targeting southern bluefin,bigeye, albacore and yellowfin. There is amajor Japanese southern bluefin fishery in thelatter part of the year just outside thesouthwestern boundary of the AFZ. Longlinersfrom Taiwan target albacore to the north andwest of the AFZ. In international waters

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between northern Australia and Indonesia thereis an Indonesian-based longline fishery,involving several hundred vessels fromIndonesia and Taiwan, targeting bigeye andyellowfin for airfreighting fresh to sashimimarkets in Japan.

There is a major purse-seine fishery forskipjack, yellowfin and bigeye in the tropicalwestern Indian Ocean, with total catches ofabout 300 000 t. The purse-seine fishery takesadult yellowfin and bigeye in addition tojuvenile yellowfin, bigeye and skipjack.Artisanal or subsistence gillnet, pole-and-lineand troll fisheries along the coasts of thenorthern Indian Ocean and Maldives take about250 000 t of skipjack and yellowfin per year. Inshallower (Continental Shelf) regions, annualcatches of kawa kawa (Euthynnus affinis) andlongtail approach 150 000 t, making animportant contribution to the raw material forThai and Indonesian canneries.

The 2002 and 2003 fishery

The 2002 domestic catch of 3015 t againsurpassed the peak Japanese combined longlinecatch of tuna and billfish—2219 t in 1984—inthe SWTBF area of the AFZ. However,SWTBF longline catches then declined, with atotal of 1764 t of tuna and billfish reported inlogbooks for 2003. The target species wereswordfish (1184 t in 2003), bigeye (205 t) andyellowfin (191 t).

The SWTBF accounts for a small percentage(<0.5%) of the total tuna and billfish catch inthe Indian Ocean. The most recent catchestimate for the Indian Ocean is for 2001: about1.292 million t of tuna, tuna-like species (e.g.Spanish mackerels—Scomberomorus spp.) andbillfish. The resources are important to IndianOcean coastal communities as well asindustrial fishers. Tropical tunas dominate theIndian Ocean catches, with an estimated catchof 407 364 t of skipjack, 281 570 t of yellowfinand 111 219 t of bigeye in 2001. Total catchesof swordfish in the Indian Ocean declinedsignificantly from over 35 000 t in the late1990s to 30 191 t in 2001.

Effort

AFMA controls the SWTBF through limitedentry. It issued a total of 90 domestic longlinepermits in 2002; 38 permits provided access tothe southern sector only, 6 to the western sectoronly, and 46 to both sectors. The number ofactive longliners increased from 5 in 1997 to46 in 2001, but decreased to 27 in 2003.Fishing effort peaked at around 6 million hooksper year in 2000–02, before declining to4 million hooks in 2003.

Before 2000, fishing had not extendedbeyond the AFZ and most activity was on thecontinental slope, just beyond the shelf, in thePerth–Shark Bay and Exmouth–Karratha areas.With the replacement of small (15–20 m)longliners by larger vessels, the fleet’s capacityto operate on wider grounds increased, so thatconsiderable activity was been reported outsidethe AFZ in the Bunbury–Carnarvon regionsince 2002. No longliners fished in the AFZaround the Cocos (Keeling) or Christmasislands.

Catch rates

Nominal catch rates of the principal targetspecies (swordfish, bigeye and yellowfin) for2003 declined from previous levels. Swordfishcatch rates in the western sector of the SWTBF,for example, declined from about330 kg/1000 hooks in 2001–02 to314 kg/1000 hooks; in the southern sector theydeclined from about 370 kg/1000 hooks to188 kg/1000 hooks. The decline in fishing

SwordfishYellowfin tunaBigeye tunaOther

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activity is attributed to poor financial returnsfrom longlining, driven by increased operatingcosts, and low prices, exchange rates and catchrates. Some operators have interests in otheractivities, such as lobster fishing, that they canengage in when longlining is less profitable.

Current monitoring and research

The Commonwealth introduced pelagic-fisheries logbooks in the early 1980s, but theywere not collected regularly, so the quality ofthe data series was consequently poor. Logbookreturns were much improved when the longlinefishery expanded in the mid-1990s becauseAFMA required them as a condition of fishingpermits. However, the quality of the SWTBFlogbook data was uncertain. In 2000 AFMAestablished a program to monitor the size- andspecies-composition of the landings received

by processors. The long-term goal is to developsystems for processors to provide size- andspecies-composition data from ports across theSWTBF.

The complex distribution of swordfish andsexual differences in growth rates mean thatsize-data needs to be linked to auxiliary data onboth the location of catches and the ratio ofmales to females. This requires monitoring atsea, because swordfish are brought to portalready gilled and gutted. The Bureau of RuralSciences (BRS), with funding from AFMA,coordinated the placement of observers onSWTBF longliners during 2003–04. The aimwas to recommend protocols and coveragelevels as the basis for a routine observerprogram that would cost-effectively meetconservation and management requirements forthe fishery. The program also collected catchand size data on target and non-target species,including protected species and other marinewildlife.

The logbook coverage of 18 years ofJapanese longline operations in the AFZ wassupported by the occasional deployment ofAustralian observers on some of the vessels.The observers verified catch-reporting andcollected biological and fisheries data. Thelongline-logbook, radio-report and observerdata that were collected are now a valuablesource of information for assessments relevantto the developing domestic longline fishery.

The Southern and Western Tuna and BillfishFishery Management Advisory Committee(MAC) provides advice on management andresearch issues. Its members are from thecommercial and recreational sectors,conservation interests, the scientificcommunity, State/Territory governments andAFMA. The current research priorities are tomitigate the effects of fishing on the broaderecosystem and improve the understanding ofthe stock structure of target species (bigeye,yellowfin and swordfish) in the eastern IndianOcean. The results will reduce uncertainty insetting total allowable catches (TACs). Currentresearch priorities are listed below:

Line hauling takes several hours, and fish catchesare comparatively few


• Investigate the stock structure of bigeye andswordfish in the eastern Indian Ocean, withparticular emphasis on determining therelationship between fish caught within theSWTBF and those caught in nearby watersand the broader Indian Ocean

• Establish a tagging program in the easternIndian Ocean to improve knowledge ofmortality rates, movements and stock structure

• Monitor catch and effort by the recreationaland charter fishing sectors targeting highlymigratory fishes

EffortPermitsActive vessels

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• Determine key biological parameters (age,growth, reproduction) required forassessment of Indian Ocean populations ofbigeye, yellowfin and swordfish stocks

• Assess the impact and reliance of theSWTBF on the pelagic ecosystem, includingtrophic linkages and the impact of fishing onecologically related species

• Develop ecological indicators, referencepoints and mitigation measures to reduceimpacts

• Develop strategies to reduce the damage andloss of catch through predation

Genetic studies of the stock structure ofbigeye and swordfish in the eastern IndianOcean have been inconclusive. CSIRO iscurrently examining new approaches. It is alsoexamining techniques to determine the age ofbigeye and swordfish. Major tagging programsfor tropical tunas in the Indian Ocean havebeen initiated with over A$20 million infunding from several sources, including theEuropean Union and Japan.

CSIRO is investigating fishery-performanceindicators (e.g., catch, catch rates and fish size)to assist with long-term management ofswordfish in SWTBF. Results from a similarstudy in the Eastern Tuna and Billfish Fishery(ETBF) suggested that changes in the meanweight of the largest swordfish in longlinecatches may be a better indicator of swordfishabundance than catch rates.

Status of stocks

In 1996, a BRS review of Indian Ocean tunaand billfish fisheries set the SWTBF in aregional context and provided an informationsource for industry, management and research.It pointed to uncertainty about the status of thetuna and billfish resources of the region.Intensive international fishing activity in thewestern Indian Ocean may impact on theresource components in the eastern IndianOcean. In particular, it noted that the status ofbigeye and swordfish remained uncertain. Asynopsis of western billfish stocks andfisheries, gathering together a wide range of

data and information, was completed in 1998.It concluded that the status of Indian Oceanbillfish stocks is unclear, with significantuncertainty arising from poor and incompletedata, the lack of a targeted fishery and changesin fishing activities. The IOTC’s Working Partyon Tropical Tunas and Working Party onBillfish is investigating these issues. However,the current status of the various billfish speciesremains uncertain.

By contrast, knowledge of the biology andstatus of commercially valuable tuna andswordfish in the Indian Ocean have improved.Summaries of information on biology andstock status for yellowfin, bigeye and swordfishare provided below. There has been noassessment of the status of albacore tuna in theIndian Ocean for several years and areconsidered to be not overfished. They are notcurrently a major target species in the SWTBF.

Yellowfin tuna

S T A T U S : Probably only moderately fished in and adjacent to the SWTBF, but status isuncertain in the western Indian Ocean.

Yellowfin live in tropical and subtropicalwaters, are fast-growing and mature at abouttwo years of age (~25 kg). They spawn wheresea-surface temperatures are at least 26˚C, andin equatorial waters may spawn every one ortwo days over several months. A mature

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yellowfin is capable of releasing millions ofeggs. Although this species may grow to180 cm in length and over 100 kg in weightwhen they are six years or older, the averagedressed weight of those caught by Australianlongliners in the Indian Ocean is less than40 kg.

Current stock assessments assume a singleyellowfin stock, although the stock structure isunclear. Longline catches of yellowfin aremade continuously across the tropical IndianOcean. Genetic studies have been inconclusive.On the other hand, no recaptures of longline-caught yellowfin tagged and released in thewestern Indian Ocean have been reported eastof the Maldives; however, this was a relativelysmall study, with few fish recaptured.

In 2003 the IOTC Working Party on TropicalTunas considered various production and age-structured models, which generally producedconsistent results. The Working Party foundthat there has been a steady increase in fishingmortality since 1980, accompanied by asubstantial decline in biomass in the mid-1980s. Catchability in the purse-seine fisheryhad increased, possibly as a result of the use ofdrifting fish aggregation devices (FADs). Theyconcluded that current catch levels are near, orpossibly above, the level that would produceMSY and that fishing mortality should not beallowed to increase above the 2000 level.However, recent catches have surpassed the2000 level. Continued purse-seining on FADswill increase the mortality of juvenile yellowfinand further reduce the yellowfin stock biomass.The IOTC is yet to introduce measures that willsignificantly limit the catch of juvenileyellowfin (and bigeye).

In the SWTBF, nominal catch rates ofyellowfin have declined substantially since2001. Uncertainty remains whether longlinecatch rates here are affected by broader IndianOcean longlining (e.g., the largeIndonesia–Taiwan fishery adjacent to theSWTBF), from intensive western Indian Oceanpurse-seining or from artisanal fisheriesthroughout the tropical Indian Ocean.Management decisions are complicated byuncertainties about the degree of mixing

between the SWTBF and broader regions.Regardless, the optimisation of economicbenefits may warrant SWTBF effort or catchcontrols because of the possibility of localdepletion in the AFZ.

Bigeye tuna

S T A T U S : Not overfished but overfishingis occurring, particularly in the westernIndian Ocean.

Bigeye are slower growing than yellowfin,maturing when about three years old andreaching 200 cm and over 180 kg when eightyears or older. They spawn in equatorial watersthroughout the year. Bigeye have a widedistribution latitudinally, but also by depthbecause of their tolerance to low oxygen levelsand low temperatures. For example, adultbigeye are normally below 150–300 m duringthe day, often moving into warmer surfacewaters at night to feed. In the Pacific Ocean,bigeye have been shown to be capable of long-range movements, perhaps across the entirePacific, but tag-recaptures also show manyremaining in one area, which suggests theremay be some stock structuring. There is nocorresponding information for bigeye in theIndian Ocean.

The origin of bigeye recruits to the westernAFZ is not known, nor is there a specificbigeye assessment for the SWTBF. It is

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unlikely that bigeye represent a separate stockin the SWTBF, but there could be some degreeof isolation from the broader Indian Oceanresource.

IOTC’s Working Party on Tropical Tunasused age-structured models in 2003 to assessthe status of bigeye in the Indian Ocean. Themodels indicated that bigeye biomass wasabove the size at MSY suggesting that thestatus is not overfished. However, recentcatches are above MSY and overfishing isoccurring. There is considerable uncertainty inthe assessment, arising from unquantifiedimprovements in fishing efficiency, inadequatesize data from recent longline catches and poorestimates of bigeye growth and mortality rates.In the western Indian Ocean, there has been arapid increase in the number of juvenile bigeyecaught by purse-seine fishing around driftingFADs. Adult skipjack, and juvenile and adultyellowfin, are also taken in this way. Thebigeye are slower growing and later maturingthan these other tuna species. The WorkingParty concluded that the biomass will soon fallbelow sustainable levels if the current patternsof fishing continue.

Broadbill swordfish

S T A T U S : Fully fished in Indian Ocean andthe SWTBF; it should be monitored closelyin the SWTBF for localised depletionassociated with intensive fishing.

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Indian Ocean swordfish

Swordfish, like bigeye and yellowfin, has awide Indian Ocean distribution. During the day,swordfish may live in deep waters (down to600 m, although they may dive to 1000 m),making nightly feeding migrations to surfacewaters. Changes in catch rates in local areasraise the possibility of there being sub-stocksof Indian Ocean swordfish; however, geneticstudies have not pointed to spatialheterogeneity.

Swordfish may grow to 550 kg or more,growing rapidly during their first two years oflife, after which females grow faster thanmales. Females also reach much larger sizesthan males; most swordfish larger than about200 kg are female. Females are sexually matureat around four years of age or 50–60 kg wholeweight, whereas males mature by about twoyears or 20 kg. Most swordfish taken bySWTBF longliners are 20–100 kg, averagingabout 50 kg. Large fish (>150 kg) were animportant component of the fishery in its earlyyears. Like yellowfin and bigeye, swordfishhave a large reproductive capacity, and canspawn throughout the tropics.

Globally, the average size of swordfish takenby longline tends to increase with latitude.Fishers in the western sector of the SWTBFhave reported very high catch rates of verysmall (<2 kg) swordfish in the north.Presumably the juvenile swordfish commonlyfound in tropical and subtropical watersmigrate to higher latitudes as they mature. Incontrast, the large, solitary adult swordfish aremost abundant at 15–35˚ north and south of theequator. Swordfish distribution also varies withsex: larger females are more common at higherlatitudes and males more common in tropicaland subtropical waters.

In 2003 the IOTC Working Party on Billfishreviewed trends in standardised catch rates forthe longline fleets of Japan and Taiwan. Japan’slongliners showed large declines since 1990whereas those of Taiwan’s longliners showedeither no trend or less marked declines in mostareas of the Indian Ocean. Preliminary fits ofproduction models suggested that swordfishbiomass is near or below the size at MSY.However, there are many weaknesses in the


assessment, such as uncertainties about stockstructure and the effects of variations intargeting. The mean weights of swordfish takenby various fleets showed no clear trend duringthe 1990s. The Working Party concluded thatthe rapid increase in swordfish catchesthroughout the Indian Ocean in the late 1990sis unlikely to be sustainable in the long-term.

In the SWTBF, the status of the swordfishresource is uncertain. The impact of domesticcatches in recent years will depend on stockstructure and the mixing rates between thewider Indian Ocean fishery and the SWTBF. If,for example, the swordfish harvested in theSWTBF are a predominantly local stock, thencatch rates might decline as the biomass isfished down. However, this also could happenif the stock is a common one and broaderIndian Ocean catches prove unsustainable. Anadditional complication is that, in either case, adecline in availability may be difficult to

identify from catch rates alone. Fishingefficiency probably increased when largervessels joined the SWTBF fleet and as fishersgained experience and developed skills intargeting swordfish. Changes in the size-composition of the catch might provide analternative indicator of stock status, especiallysince most large swordfish caught by longlineare female and female swordfish mature atmuch larger sizes than males do.

A BRS review of swordfish fisheries in otherparts of the world showed that, without propercontrols, fishing effort in swordfish fisheriesoften expanded to overshoot the optimum level.Such experiences suggest that Australianfisheries managers will need to monitor andcontrol longline effort carefully. The SWTBFlongline fleet has the potential to overfishswordfish, so operators will need to developmore sustainable, multi-species activities tomaintain long-term viability.

This large super-seiner fishes for tunas in the western Indian Ocean


Environmental issues

Environmental issues in the SWTBF includethe catch and release of black and blue marlin;interactions with seabirds and sea turtles; andthe discarding and loss of fishing gear andpackaging.

In response to bycatch issues, AFMAformulated a Bycatch Action Plan for the threeCommonwealth tuna fisheries (SWTBF, ETBFand Southern Bluefin Tuna Fishery). Over 60marine species have been recorded from AFZlongline catches, including tuna and tuna-likefish, billfish, sharks, rays, various other fish,seabirds, and (rarely) sea turtles and marinemammals. When Japanese longliners wereoperating in the fishery, they retained about 30species (mainly the tunas, billfishes and sharks)for commercial sale. The bycatch species (mostcommonly blue shark, Prionace glauca) werereleased or discarded at sea. The 2003–04 pilotscientific monitoring program found thatdomestic longliners frequently catch blue sharkand crocodile shark (Pseudocarchariuskamoharai). The latter are quite uncommon inother longline fisheries. Commercial marketshave developed in Australia and overseas forseveral bycatch species, including escolar orblack oilfish (Lepidocybium flavobrunneum),oilfish (Ruvettus pretiosus) and dolphinfish ormahi mahi (Coryphaena hippurus). Severalother species, such as wahoo (Acanthocybiumsolandri), have commercial potential.

A 2001 BRS report highlighted high levelsof shark bycatch and the widespread practice of‘shark finning’ in Australia’s tuna fisheries,particularly in the ETBF and the SWTBF.Fishery-specific arrangements are required toincrease knowledge about shark catches andtheir sustainability. In the interim, AFMA hasbanned the practice of finning sharks at sea,prohibiting the possession or landing of finsseparate from carcasses. AFMA has enforcedthe landing limit of 20 sharks per vessel perfishing trip, and also banned wire traces (whichincrease the likelihood of retaining shark).

Marine mammals and sharks sometimescreate problems for fishers by removing ordamaging hooked fish before the longline ishauled. The IOTC has endorsed a proposal forresearch on such predation problems. TheJapan National Research Institute of Far SeasFisheries has prepared a standard reportingform for distribution among tuna longlinersoperating in the Pacific and Atlantic as well asin the Indian Ocean. A scientific workshop willanalyse survey results in 2006.

Longline closures north of Hawaii and onthe Grand Banks (North Atlantic) have beenintroduced because of public concern overincidental catches of sea turtles duringswordfish longlining. Catches of sea turtleshave been reported in SWTBF logbooks andduring interviews with operators. The 2003–04pilot scientific monitoring program reportedlow catch rates of sea turtles.

Seabirds, such as albatrosses andshearwaters, are attracted to longline baitswhen vessels are setting their gear, and somebirds become hooked and drowned. In August1998 the Minister for the Environmentapproved a Threat Abatement Plan to reducethe incidental catch of seabirds by longliners.The chapter on the Eastern Tuna and BillfishFishery details progress in identifying longlinefishing practices intended to reduce themortality of seabirds. All SWTBF operators arecurrently required to carry an approved bird-scaring ‘tori’ line, to use it and set theirlonglines only at night when operating south of30ºS, and to not discharge offal during linesetting and hauling.

The moonfish (or ‘opah’) is a popular table fish, sothey are killed and processed quickly to maintainflesh quality


Further reading

Campbell, R.A., Tuck, G.N., Pepperell, J.G.and Larcombe, J.W.P. (1998) Synopsis onthe Billfish Stocks and Fisheries within theWestern AFZ and the Indian Ocean.Australian Fisheries Management Authority,Canberra, 122 pp.

Deriso, R.B., Bayliff, W.H. and Webb, N.J.(1998) Proceedings of the First WorldMeeting on Bigeye Tuna. IATTC SpecialReport 9, Inter-American Tropical TunaCommission, La Jolla, California, UnitedStates.

Falterman, B., Pepperell, J. and Graves, J.(2000) Population Genetics and StockStructure of Black Marlin (Makaira indica)in the Pacific and Indian Oceans. Report toAustralian Fisheries Management Authority,Canberra, 97 pp.

Larcombe, J.W.P., Caton, A., Williams, D.McB.and Speare, P.J. (1997) Western Tuna andBillfish Fisheries Research. Bureau ofResource Sciences, Canberra, 205 pp.

Rose, C. and McLoughlin, K. (2001) Review ofShark Finning in Australian Fisheries. FinalReport to Fisheries Resources ResearchFund. Bureau of Resource Sciences,Canberra, 166 pp.

Management performance

Until recently, the SWTBF was among thefastest-growing fisheries in Australia. The useof limited entry to control fishing effort is nowconsidered to be inadequate for effectivemanagement. In the new management plan,which is to be known as the “WTBFmanagement plan”, individual transferablequotas (ITQs) will be the principalmanagement tool. The quotas will be setinitially for swordfish, yellowfin, bigeye andstriped marlin. Other species, both target andnon-target, will be monitored to determine anyfuture need for quota management. AlthoughITQs have been identified as the preferredmethod of control, the limited amount of dataavailable from the fishery and the regional

extent of the key stocks present problems forestimating appropriate TACs. Management ofthe fishery should be adaptive, and allow forupward or downward adjustment of TACs whennew information becomes available. For thisreason, development of a management strategywith biological reference points and decisionrules has been identified as a key task for theSWTBF MAC.

The stock structure of the main targetspecies in the SWTBF is poorly known.Nevertheless, it is clear that SWTBFmanagement must consider the possible levelof interaction with tuna and billfish fisheries inthe broader Indian Ocean. This complicates theimplementation of effective domesticmanagement for what is a small sector of thefishery—the approach adopted internationallymay necessitate domestic adjustment ofmanagement arrangements. Furthermore,management arrangements established for theSWTBF will need to comply with the UnitedNations Fish Stocks Agreement (1995) thatentered into force on 11 December 2001.

It is highly likely that there is significantinteraction among the major longline fisheriesoperating in the eastern Indian Ocean, with thefleets from Australia, Indonesia, Japan, Koreaand Taiwan probably exploiting commonstocks of bigeye, yellowfin and, perhaps,swordfish. Further research is required toascertain whether these are the same stocksexploited by the purse-seine fleets of theEuropean Union, which operate predominantlyin the tropical western Indian Ocean. Theoutcomes of research on the structure of stocksin the Indian Ocean will affect the futuremanagement of the fishery.

The IOTC has yet to implement anysignificant management measures for IndianOcean tuna fisheries. As early as 1999, itsScientific Committee concluded that bigeyewere likely to be fully fished or overfished inthe Indian Ocean. The committee suggestedthat the catch of juvenile bigeye by purse-seiners fishing on FADs had contributed to thedecline in biomass, and that longline and purse-seine effort should not be increased. The IOTC


requested advice on the impact that varioustime and area closures might have on mortalitylevels and on the fisheries. In 2000, the IOTCdecided against introducing FAD-exclusionareas, despite the likely benefits in reducingjuvenile bigeye mortality. This decision waspartly linked to the effects of those regulationson the economic viability of the industrialpurse-seine fleet. In 2003, on the basis offurther scientific evidence, Australia introduceda revised proposal for a FAD-exclusion area.However, the European Union stronglyopposed the proposal and the resolution did notproceed. In the same year, Australia proposedto establish a group to investigate nationalallocation criteria for tropical tunas in theIndian Ocean, but this was also rejected.Instead, IOTC agreed to establish a workinggroup to consider conservation andmanagement options that may be applicable totuna and billfish.

In 2001, based on analysis of catch andeffort data from the Japanese longline fisheryand from the longline fishery for swordfish atLa Réunion, the IOTC Working Party onBillfish concluded that the abundance ofswordfish in the Indian Ocean was likely todecrease significantly. There has been asubstantial increase in the effort that targetsswordfish in the Western Indian Ocean, notablyby the Spanish fleet. The IOTC has not madeany clear statement about the status ofswordfish stocks in the Indian Ocean. However,the increases in the SWTBF catch of swordfish,

followed by sudden declines, is of concern inAustralia. Currently there is no reliable stockassessment for SWTBF swordfish. Analyses ofother swordfish fisheries suggest that theaverage size of swordfish caught is a goodindicator of stock status. SWTBF MACrecognised the need for size-compositionmonitoring in the fishery, and it has been anearly research activity. However, further yearsof data collection will be required before anyrobust conclusion can be drawn from thisindicator of stock status.

Regardless of current catch levels, theapplication of the precautionary approachrequires the prompt adoption of measures toprevent possible declines in SWTBF stocks.Trends in the ETBF and other swordfish-targetfisheries highlight the need for a cautiousapproach to fishery management. Retention ofthe current input controls in the SWTBF, andthe establishment of ITQs for swordfish, willbe important elements of effective managementof this species.

Catches in the SWTBF have increased withthe geographical expansion of fishing activities.Until the mid-1990s, longline activity wasconcentrated within the AFZ off the centralcoast of Western Australia, but now extendsfrom the Great Australian Bight to the NorthWest Shelf and beyond the AFZ. The largegeographical extent of the SWTBF complicatesthe fishery’s management. For example, someoperators target yellowfin in tropical waters offthe North West Shelf, while others seek high-value bigeye south of 35˚S latitude. Althoughoperating in a similar fishery from amanagement perspective, they fish in differentbiogeographical regions and catch a differentsuite of species. Assessment of potentialenvironmental impacts of the fishery requiresdetailed information from each biogeographicalregion of the fishery. The fishing entitlementsof some operators in the SWTBF restrictedthem to waters either south or north of 34˚S,and acted as a partial control of effort in thetwo zones. However, the new management planwill introduce ITQs and remove themanagement distinction between the zones,relaxing controls on fishing effort.

Landing a large broadbill swordfish

southern and western tuna and billfish...

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