Western Tuna and Billfish Fishery - Attachment 1...Western Tuna and Billfish Fishery 81 fleet’s annual catch ranged up to 125 t of swordfish, 1034 t of bigeye tuna and 1052 t of

Western Tuna and Billfish Fishery 77

Western Tuna and Billfish Fishery

Main features

S T A T U S

• Bigeye tuna, yellowfin tuna andbroadbill swordfish: not overfished.

• Overfishing of yellowfin tuna andbroadbill swordfish in the broaderIndian Ocean.

• Bigeye tuna: overfishing status uncertain.

• Albacore tuna and striped marlin:overfishing and overfished status uncertain.

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

• Ocean-wide assessments of key speciesthrough the Indian Ocean TunaCommission (IOTC) require furtherdevelopment and improved data.

• Assessments unreliable for the AustralianFishing Zone (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 ( 2 0 0 7 )

• Annual catches since 2004 (confidentialbecause fewer than five vessels fished)averaged around 420 t.

• Tuna and billfish catch in 2004 about700 t (swordfish 366 t; bigeye tuna 90 t;yellowfin tuna 151 t).

• Valued at $2.2 million (2006–07).

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 catches of tunaand billfish peaked in 1984 at 2219 t(including 1052 t of yellowfin).

• Domestic catches exceeded 3000 t in2001 and 2002.

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

• Control of total catch of target species,adjusted as stock dynamics becomebetter understood.

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

• Input controls, including limited entry,gear and area restrictions.

• Bycatch restrictions.

• Output controls via individualtransferable quotas (ITQs) under theWestern Tuna and Billfish ManagementPlan 2005 to be implemented in 2008.

• Harvest strategy framework developedfor implementation in 2009.

F I S H E R Y S T A T U S R E V I E W S

T U N A A N D B I L L F I S H F I S H E R I E S

78 Fishery Status Reports | 2 0 0 7 |

Domestic management mustaccommodate internationalarrangements established by the IOTC.Implementation of total allowablecatches (TACs) and ITQs is beingfinalised. Following the acceptance of a statutory management plan for thefishery, statutory fishing rights (SFRs)have been provisionally granted,subject to appeal.

About 1.5 million tonnes of tuna andbillfish are caught in the Indian Oceaneach year (1.6 million in 2006), withclose to half taken by industriallongline and purse-seine fleets.

Effective region-wide managementaction is required because currentIndian Ocean catch levels of bigeyetuna, yellowfin tuna and swordfish are unlikely to be sustainable in thelong term.

HighlightsThe Western Tuna and Billfish Fishery(WTBF) developed rapidly afterJapanese longliners were excludedfrom the AFZ in 1997. Hook setsincreased more than tenfold and thetotal catch sixfold.

Catch levels and fishing effort havedeclined since 2002 because of lowprices and higher operating costs;fewer than five vessels have operatedeach year from 2005 to 2007.

The longline fishery targets broadbillswordfish, bigeye tuna and yellowfintuna, with most of the catch historicallyexported fresh-chilled to markets inJapan and the United States, althoughrecent changes have seen freezing ofsome of the catch and increasedmarketing in Australia.

Perth

Bunbury

Geraldton

Esperance

Carnarvon

Albany

Port Hedland

125°E

125°E

120°E

120°E

115°E

115°E

110°E

110°E

105°E

105°E

100°E

100°E

20°S 20°S

25°S 25°S

30°S 30°S

35°S 35°S

Perth

Bunbury

Geraldton

Esperance

Carnarvon

Albany

Port Hedland

125°E

125°E

120°E

120°E

115°E

115°E

110°E

110°E

105°E

105°E

100°E

100°E

20°S 20°S

25°S 25°S

30°S 30°S

35°S 35°SWestern Tuna and Billfish Fishery Longline sector (2003–07)Relative fishing intensity

Low Medium

High

Limit of theAustralianFishing Zone

Karratha

Western Australia

200 m

200 m


Background

History of the fishery

The WTBF (previously known as the

Southern and Western Tuna and Billfish

Fishery) extends from 141° E (the South

Australia–Victoria border) around western

and northern Australia to Cape York in

Queensland. However, the commercially

valuable tuna and billfish species are rare in

the shallow northern region of the AFZ, so

fishing activities have been concentrated in

oceanic waters along the western and

southern coasts. A management plan for the

fishery came into force in October 2005, and

SFRs have been provisionally granted

(subject to appeal). SFRs will be allocated as

ITQs for four species: bigeye tuna (Thunnusobesus), yellowfin tuna (T. albacares),

broadbill swordfish (Xiphius gladius) and

striped marlin (Tetrapturus audax).

The large geographical extent of the

WTBF complicates the fishery’s management.

For example, some operators have targeted

yellowfin tuna in tropical waters off the North

West Shelf, while others have sought high-

value bigeye tuna south of 35° S. Although

operating in a fishery that is similar from a

management perspective, they fish in different

biogeographical regions and catch a different

suite of species. Assessment of potential

environmental impacts of the fishery requires

detailed information from each

biogeographical region.

An intensive surface fishery for southern

bluefin tuna (T. maccoyii) developed off

South Australia in the 1950s and also

operated in the Albany–Esperance area

between 1970 and 1988, using trolling, bait-

and-pole and (off South Australia) purse-seine

techniques. Otherwise, domestic tuna-fishing

activity off Western Australia had been

limited to opportunistic handline operations

from local trawl and rock-lobster vessels, and

trolling by recreational gamefishers.

Historically, the main WTBF catch was

taken by Japanese pelagic longliners, after

1979 operating in the AFZ under bilateral

agreements. They targeted high-value bigeye

tuna in the south-west and yellowfin tuna and

striped marlin in the north-west, but have

been excluded from Australian waters since

November 1997. A domestic longline fishery

has replaced them, using monofilament

mainline gear and concentrating on broadbill

swordfish, in addition to bigeye tuna and

yellowfin tuna. Catches of albacore tuna

(T. alalunga), longtail tuna (T. tonggol) and

southern bluefin tuna are also made. In the

South Australian area where the surface

fishery for southern bluefin tuna operates,

skipjack tuna (Katsuwonus pelamis) is an

occasional late-season (March–April) target

of purse seiners (see the Skipjack fisherieschapter).

The WTBF is contiguous with larger tuna

and billfish fisheries within Indonesia’s

Exclusive Economic Zone and elsewhere in

the Indian Ocean. Australia is a member of

the IOTC, a multilateral organisation with 25

members, established under the United

Nations Convention on the Law of the Sea.

The IOTC provides a mechanism for

encouraging participants in Indian Ocean tuna

fisheries to comply with international

conservation and management measures. It is

also a forum for stock assessment and

regional management of Indian Ocean tuna

and billfish.

Interest in the WTBF increased

significantly in 1998, with an increase in

investment and prices paid for the transfer of

fishing permits. About 20 vessels operated,

eight of which caught over 35 t each. In

previous years there were few, if any,

dedicated WTBF domestic longline vessels,

and most longliners were Japanese. However,

in 1998 a number of larger vessels were

renovated extensively for longlining and two

new ones were built.

Most longliners that have operated in the

WTBF have been 15–30 m long and have

deployed monofilament longline gear,

undertaking trips that were generally of 3–10

days, with about 1000 hooks deployed before

sunrise each day. These vessels stored their

catch on ice, in ice slurry or in brine-spray

systems. Before 2000, fishing had not


extended beyond the AFZ and most activity

was on the continental slope, just beyond the

shelf, in the Perth – Shark Bay and

Exmouth–Karratha areas. With the

replacement of small (15–20 m) longliners by

larger vessels, the fleet’s capacity to operate

on wider grounds increased, leading to

considerable activity being reported outside

the AFZ and longer fishing trips. Longliners

that target swordfish make shallow (20–120 m)

sets at night, using squid baits and chemical

light-sticks. The catch has recently been

landed almost exclusively in Fremantle and

Geraldton.

Western Australia has an active

recreational game fishery, targeting sailfish

(Istiophorus platypterus), black marlin

(Makaira indica), blue marlin (M. nigricans),

striped marlin and yellowfin tuna.

Consideration of recreational fishing interests

in the late 1980s resulted in the prohibition of

Japanese longlining within 50 nm of the

Western Australian coast. It also led to

Japanese agreement that billfish other than

swordfish would not be targeted, and that all

black and blue marlin taken alive would be

released. In 1994, Western Australia

legislated to prevent the landing for

commercial sale of all billfish of the

Istiophoridae family. The legislation was not

enforced until December 1999 and was

overridden by changes to Commonwealth

legislation in 2005. In 1998, the Australian

Government banned the retention of blue and

black marlin, whether alive or dead, taken

anywhere in the AFZ by commercial fishing.

In October 2005, resource-sharing policy

arrangements were announced by the then

Minister for Fisheries, Forestry and

Conservation. Implementation of those

arrangements, which specify restrictions on

the areas to be fished by longline vessels to

allow use of areas by recreational fishers, is

under discussion. Longtail tuna are also taken

by recreational fishers, so a bycatch limit of

35 t has been introduced to the WTBF for

that species.

In the past, Japanese longliners have taken

good catches of bigeye tuna and yellowfin

tuna in the Christmas Island and Cocos

(Keeling) Islands regions of the AFZ. The

Australian Fisheries Management Authority

(AFMA) permitted some domestic longlining

under a controlled-fishing program but there

has been very little activity, probably because

of the remoteness of the islands from the

Australian mainland, limited support facilities

and difficulties in transporting fresh product

to overseas markets. The existence of

endangered seabirds endemic to the region

will require appropriate controls on fishing

practices.

Japan began pelagic longlining off

Australia in the 1950s. The large (40–55 m)

freezer longliners remained at sea for 2–3

months, deploying 2500–3500 hooks each

day on 60-nm multistrand mainlines. The

0

1

2

3

4

5

1983 1987 1991 1995 1999 2003 2007

0

2

4

6

Catch & Effort: longline, WTBF

*

Domestic catchJapanese catchDomestic effortJapanese effortConfidential data

Cat

ch (

thou

sand

tonn

es)

Effo

rt (

mill

ion

hook

s)

* * *

0

1

2

3

4

1983 1987 1991 1995 1999 2003 2007

Catch: Australian fishery, WTBF

*

SwordfishYellowfin tunaBigeye tunaOtherConfidential data

Cat

ch (

thou

sand

tonn

es)

* * *


fleet’s annual catch ranged up to 125 t of

swordfish, 1034 t of bigeye tuna and 1052 t of

yellowfin tuna. After implementation of the

AFZ in 1979, Japanese activity in the zone

was licensed under bilateral agreements. The

peak annual catch of tuna and billfish

combined was 2219 t, reported in 1984.

Australia progressively restricted areas of

access until Japan’s longliners were totally

excluded in November 1997.

The IOTC vessel registry for the Indian

Ocean identifies almost 1800 individual tuna

vessels longer than 24 m, flying 33 different

state flags, although fewer vessels fish in any

year. Gear types include longline, purse seine,

gillnet and pole-and-line. The number of

artisanal tuna vessels, fishing mainly in the

exclusive economic zones of Indian Ocean

littoral states, is in the tens of thousands. In

general, the artisanal vessels have a short

range, no freezer capacity and limited storage.

Their catch is typically sold at local markets.

Many longliners from Japan, South Korea

and Taiwan fish high-seas areas across the

Indian Ocean, targeting southern bluefin,

bigeye, albacore and yellowfin tunas. There is

a major Japanese southern bluefin tuna

fishery in the later part of the year just outside

the south-western boundary of the AFZ.

Longliners from Taiwan target albacore tuna

to the north and west of the AFZ. In

international waters between northern

Australia and Indonesia, an Indonesian-based

longline fishery comprising several hundred

vessels from Indonesia and Taiwan targets

bigeye tuna and yellowfin tuna, airfreighting

fresh fish to sashimi markets in Japan.

There is a major purse-seine fishery for

skipjack, yellowfin and bigeye tunas in the

tropical western Indian Ocean, with total

catches of more than 400 000 t. The purse-

seine fishery takes adult yellowfin and bigeye

tuna, as well as juvenile yellowfin, bigeye and

skipjack tuna. Artisanal or subsistence gillnet,

pole-and-line and troll fisheries along the

coasts of the northern Indian Ocean and

Maldives take about 250 000 t of skipjack

tuna and yellowfin tuna per year. In shallower

(continental shelf) regions, annual catches of

kawa kawa (Euthynnus affinis) and longtail

tuna approach 150 000 t, making an

important contribution to the Thai and

Indonesian canneries.

The peak reported domestic catch for the

fishery was 3355 t in 2001. Catch and effort

have since declined markedly owing to lower

prices and higher operating costs. A total of

3015 t was reported in 2002, and 1764 t in

2003. The 2004 catch was 700 t (swordfish

366 t; bigeye 90 t; yellowfin tuna 151 t).

Average catch for the years from 2005 to

2007 was around 420 t.

There are currently approximately 120

permits to operate in the fishery. The numbers

of active longliners increased from 5 in 1997

to 46 in 2001, but decreased to 27 in 2003,

then to 13 in 2004, and fewer than 5 vessels

have fished each year from 2005. Fishing

effort peaked at around 6 million hooks per

year in 2000–02, before declining to 4 million

hooks in 2003 and 1.5 million in 2004. The

number of hook sets from 2005 to 2007 has

averaged around 720 000 per year.

Retrieving a tuna longline


The 2007 fisheryData on catches and effort since 2004 are

confidential because fewer than five vessels

have fished each year. At its peak, the WTBF

accounted for less than 0.5% of the total tuna

and billfish catch in the Indian Ocean. The

most recent catch estimate for the Indian

Ocean is that more than 1.6 million t of tuna,

tuna-like species (for example, Spanish

mackerels—Scomberomorus spp.) and billfish

are taken. The resources are important to

Indian Ocean coastal communities, as well as

to industrial fishers. Tropical tunas dominate

the Indian Ocean catches: the preliminary

estimates of catches in 2006 were 596 000 t

of skipjack, 493 000 t of yellowfin and

105 700 t of bigeye. Total catches of

swordfish in the Indian Ocean have declined

significantly, from over 35 000 t in the late

1990s to less than 30 000 t in 2005 and 2006.

Current monitoring andresearchThe Australian Government introduced

pelagic-fisheries logbooks in the early 1980s,

but they were not collected regularly, so the

quality of the data series was poor. Logbook

returns were much improved when the

longline fishery expanded in the mid-1990s,

because AFMA required the returns as a

condition of fishing permits. However, the

quality of the WTBF logbook data was still

uncertain. In 2000, AFMA established a

program to monitor the size- and species-

composition of the landings received by

processors.

The complex distribution of swordfish and

sexual differences in growth rates mean that

size data need to be linked both to the

location of catches and to the ratio of males

to females. This requires monitoring at sea,

because swordfish are brought to port gilled

and gutted. The Bureau of Rural Sciences

(BRS), with funding from AFMA,

coordinated the placement of observers on

WTBF longliners during the years from 2003

to 2007. The aim was to recommend

protocols and coverage levels as the basis for

a routine, cost-effective observer program that

would meet conservation and management

requirements for the fishery. The program has

collected catch and size data on target and

non-target species, including protected

species and other marine wildlife. There has

been further observer coverage for the fishery

to comply with the national Seabird Threat

Abatement Plan.

The logbook coverage of 18 years of

Japanese longline operations in the AFZ was

supported by the occasional deployment of

Australian observers on some of the vessels.

The observers verified catch reporting and

collected biological and fisheries data. The

longline-logbook, radio-report and observer

data that were collected are now a valuable

source of information for assessments

relevant to the domestic longline fishery.

The Western Tuna and Billfish Fishery

Management Advisory Committee provides

advice on management and research issues.

Its members are from the commercial and

recreational sectors, conservation interests,

the scientific community, state and territory

governments and AFMA. The current

research priorities for the fishery include:

• reviewing and refining the initial harvest

strategy developed for the fishery

• investigating the stock structure of

swordfish, bigeye tuna, yellowfin tuna and

blue shark in the eastern Indian Ocean,

with particular emphasis on determining

the relationship between fish caught within

the WTBF and those caught in nearby

waters and the broader Indian Ocean

• identifying priority species for tagging by

the recreational and industry sectors to

maximise prospects of collecting

information useful for science and

management

• determining key biological parameters

(age, growth, reproduction) required for

assessment of Indian Ocean bigeye tuna,

yellowfin tuna and swordfish stocks

• developing assessment approaches for

oceanic shark species, particularly those

identified as high-risk species

0

2

4

6

8

● ● ● ● ● ● ● ●● ● ● ●

●

●●

● ●

●

●

● ● ● ● ● ● ● ●● ● ● ●

●

●●

● ●

●

●

● ● ● ● ● ● ● ●● ● ● ●

●

●●

● ●

●

●

1986 1989 1992 1995 1998 2001 2004 2007

0

100

200

300

Effort: Australian longline, WTBF

●

EffortPermitsActive vesselsConfidential data

Effo

rt (

mill

ion

hook

s)

Per

mits

/Ves

sels

* * *

*

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1983 1987 1991 1995 1999 2003 2007

Catch: swordfish, WTBF

*

Australia (domestic and charter)Japan (bilateral and joint venture)Confidential data

Cat

ch (

thou

sand

tonn

es)

* * *

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1983 1987 1991 1995 1999 2003 2007

Catch: yellowfin tuna, WTBF

*


Cat

ch (

thou

sand

tonn

es)

* * * 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1983 1987 1991 1995 1999 2003 2007

Catch: striped marlin, WTBF

*


Cat

ch (

thou

sand

tonn

es)

* * *

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1983 1987 1991 1995 1999 2003 2007

Catch: bigeye tuna, WTBF

*


Cat

ch (

thou

sand

tonn

es)

* * *0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1983 1987 1991 1995 1999 2003 2007

Catch: albacore tuna, WTBF

*


Cat

ch (

thou

sand

tonn

es)

* * *


• developing cost-effective monitoring

strategies for the fishery

• identifying and evaluating appropriate

ecological indicators and reference points

for ecologically related species.

Genetic studies of the stock structure of

bigeye tuna and swordfish in the eastern

Indian Ocean have been inconclusive. CSIRO

is currently examining new approaches. It is

also examining techniques to determine the

age of bigeye tuna and swordfish. Major

tagging programs for tropical tunas in the

Indian Ocean have been initiated, with over

$20 million in funding from several sources

that include the European Union and Japan.

H A R V E S T S T R A T E G Y

0

100

200

300

400

500

600

700

1970 1976 1982 1988 1994 2000 2006

Catch: yellowfin tuna, Indian Ocean

Western area catchEastern area catch

Cat

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A harvest strategy framework has been

developed for the WTBF and is scheduled

for implementation in 2009. The

framework includes a ‘decision tree’ that

defines rules and subsequent adjustments

to the recommended biological catch (or

level of fishing mortality). Empirical

indicators of stock status are being used

because robust, region-specific

assessments are not available for stocks

within the WTBF.

For each target species, standardised

catch rates for three size classes (‘small’,

‘prime’ and ‘large’) will form the main

performance indicators. The values of the

indicators will be compared with target

and limit reference points. By considering

size data, the harvest strategy should be

more robust to potential biases associated

with using longline catch rates as indices

of abundance. Research is in progress to

examine the impact of uncertainty in the

linkages between the WTBF and the wider

Indian Ocean stocks on the

implementation of the strategy.

Status of stocks

Y E L L O W F I N T U N A

S T A T U S

Probably only moderately fished in andadjacent to the WTBF; not overfished in thewestern Indian Ocean, but high catchesfrom 2003 to 2006 constitute overfishingand an updated assessment incorporatingthose high catches is needed.

Yellowfin tuna live in tropical and subtropical

waters, are fast-growing and mature at about

2 years of age (~25 kg). They spawn where

sea-surface temperatures are at least 26°C,

and in equatorial waters may spawn every

1 or 2 days over several months. A mature

yellowfin is capable of releasing millions

of eggs. Although this species can grow to

180 cm long and over 100 kg when 6 years

or older, the average dressed weight of those

caught by Australian longliners in the Indian

Ocean is less than 40 kg.

Current stock assessments assume a single

yellowfin tuna stock, but the stock structure

is unclear. Longline catches of yellowfin tuna

are made continuously across the Indian

Ocean. Although genetic studies have been

inconclusive, no recaptures of longline-

caught yellowfin tuna tagged and released

in the western Indian Ocean have been

reported east of the Maldives; however,

the tag–recapture study was relatively small,

with few fish recaptured.Yellowfin tuna

0

50

100

150

200

1970 1976 1982 1988 1994 2000 2006

Catch: bigeye tuna, Indian Ocean


Cat

ch (

thou

sand

tonn

es)


In 2003, the IOTC Working Party on

Tropical Tunas found that there had been a

steady increase in fishing mortality since

1980, accompanied by a substantial decline in

biomass in the mid-1980s. Catchability in the

purse-seine fishery had increased, possibly as

a result of the use of drifting fish-aggregation

devices (FADs). The updated assessment in

2005 concluded that catch levels between

1992 and 2002 had been near the level that

would produce the maximum sustainable

yield (MSY) and that fishing mortality should

not be allowed to increase. Continued purse-

seining on FADs will increase the mortality

of juvenile yellowfin tuna and further reduce

the yellowfin tuna stock biomass. Catches

from 2003 to 2006 were well above those

levels and will not be sustainable unless

supported by very high recruitments. It is not

clear whether the high catches resulted from

previous high recruitment or an increase in

catchability over those years.

A further assessment was undertaken in

2007 based on several modelling approaches.

Despite differences in the modelling, it was

concluded that fishing levels have continued

to exceed MSY levels. Model estimates of

MSY ranged from 271 000 t to 360 000 t,

compared with the preliminary 2006 catch of

493 000 t. The IOTC is yet to introduce

measures that will significantly limit the catch

of juvenile yellowfin tuna.

In the WTBF, it remains uncertain whether

longline catch rates in and near the AFZ are

affected by broader Indian Ocean longlining

(such as longliners from Taiwan and

Indonesia operating adjacent to the WTBF),

by intensive western Indian Ocean purse-

seining or by artisanal fisheries operating

throughout the Indian Ocean. Management

decisions are complicated by uncertainties

about the degree of stock mixing between the

WTBF and broader regions.

B I G E Y E T U N A

S T A T U S

Not overfished; overfishing status uncertain,particularly in the western Indian Ocean.

Bigeye tuna are slower growing than

yellowfin tuna, maturing when about 3 years

old and reaching 200 cm and over 180 kg

when 8 years or older. They spawn in

equatorial waters throughout the year. Bigeye

tuna have a wide latitudinal distribution and,

because of their tolerance to low oxygen

levels and low temperatures, a broad depth

distribution. For example, adult bigeye are

normally below 150–300 m during the day,

and often move into warmer surface waters at

night to feed. In the Pacific Ocean, bigeye

tuna have been shown to be capable of long-

range movements, perhaps across the entire

Pacific, but tag recaptures also show that

many remain in one area, which suggests that

there may be some stock structuring. There is

no corresponding information for bigeye tuna

in the Indian Ocean.

The origin of bigeye tuna recruits to the

western AFZ is not known, and there is no

specific bigeye tuna assessment for the

WTBF. It is unlikely that bigeye tuna

represent a separate stock in the WTBF, but

there could be some isolation from the

broader Indian Ocean resource.

IOTC’s Working Party on Tropical Tunas

used age-structured models in 2004 and again

in 2006 to assess the status of bigeye tuna in

0

10

20

30

40

50

1970 1976 1982 1988 1994 2000 2006

Catch: swordfish, Indian Ocean


Cat

ch (

thou

sand

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es)


the Indian Ocean. The models indicated that

the bigeye tuna biomass was above the size

needed to achieve MSY, suggesting that the

stock is not overfished. Catches for several

years before 2005 were above MSY, implying

that overfishing was occurring. A more

optimistic assessment in 2006 and reduced

catches in 2005 suggested that the reported

take was around the estimated MSY and that

fishing mortality was below the level that

produces MSY (FMSY). MSY was estimated

to be around 111 000 t, whereas the 2006

preliminary catch estimate was 105 700 t.

The assessment results must be treated with

caution because there is concern that the

reduced catches of bigeye tuna were linked to

high catches of yellowfin tuna, and that the

pattern of fishing effort is returning to that

which produced higher catches in previous

years. There is considerable uncertainty in the

assessment, arising from unquantified

improvements in fishing efficiency,

inadequate size data from recent longline

catches, and poor estimates of bigeye tuna

growth and mortality rates. In the western

Indian Ocean, there has been a rapid increase

in the number of juvenile bigeye tuna caught

by purse-seine fishing around drifting FADs.

Adult skipjack tuna and juvenile and adult

yellowfin tuna are also taken in this way, but

they are faster growing and mature earlier

than bigeye tuna.

B R O A D B I L L S W O R D F I S H

S T A T U S

Not overfished in the Indian Ocean, althoughthere is likely localised depletion in thesouth-west; the species should bemonitored closely in the WTBF for localiseddepletion if levels of fishing effort increasesignificantly. Subject to overfishing in thewestern Indian Ocean.

Swordfish, like bigeye tuna and yellowfin

tuna, have a wide distribution in the Indian

Ocean. During the day, swordfish may live in

deep waters (down to 600 m, although they

may dive to 1000 m), making nightly feeding

migrations to surface waters. Changes in

catch rates in local areas raise the possibility

that there are substocks of Indian Ocean

swordfish; however, genetic studies have not

pointed to spatial heterogeneity.

Swordfish can grow to 550 kg or more,

growing rapidly during their first 2 years of

life, after which females grow faster than

males. Females also reach much larger sizes

than males: most swordfish larger than about

200 kg are female. Females are sexually

mature at around 4 years of age or 50–60 kg

whole weight, whereas males mature by

about 2 years or 20 kg. Most swordfish taken

by WTBF longliners are 20–100 kg,

averaging about 50 kg. Large fish (>150 kg)

were an important component of the fishery

in its early years. Like yellowfin tuna and

bigeye tuna, swordfish have a large

reproductive capacity and can spawn

throughout the tropics.

0

2

4

6

8

1970 1976 1982 1988 1994 2000 2006

Catch: striped marlin, Indian Ocean


Cat

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Globally, the average size of swordfish

taken by longline tends to increase with

latitude. Fishers in the western sector of the

WTBF have reported high catch rates of very

small (<2 kg) swordfish in the north.

Presumably, the juvenile swordfish commonly

found in tropical and subtropical waters

migrate to higher latitudes as they mature. In

contrast, large, solitary adult swordfish are

most abundant at 15–35° north and south of

the equator. Swordfish distribution also varies

with sex: larger females are more common at

higher latitudes and males more common in

tropical and subtropical waters.

In 2004, the IOTC Working Party on

Billfish reviewed trends in standardised catch

rates for the longline fleets of Japan and

Taiwan. There was a constant pattern of

decline in all areas exploited, declines for the

Japanese longliners being more pronounced.

There are large uncertainties about stock

structure and the effects of variations in

targeting. The mean weights of swordfish

taken by various fleets showed no clear trend

during the 1990s. The working party

concluded that the rapid increase in swordfish

catches throughout the Indian Ocean in the

late 1990s is unlikely to be sustainable in the

long term. An assessment by the working

party in 2006 indicated that the stock is

probably not currently overfished, but that

current levels of fishing are too high

(FCURRENT > FMSY), particularly in localised

areas in the south-west Indian Ocean. MSY

estimates ranged between 23 540 t and

27 000 t, whereas the 2006 catch estimate

was 29 000 t.

The status of the swordfish resource in the

WTBF is uncertain, although current fishing

levels are very low. The impact of domestic

catches will depend on stock structure and

mixing rates between the wider Indian Ocean

fishery and the WTBF. For example, if the

swordfish harvested in the WTBF are a local

stock, catch rates might decline as the

biomass is fished down. However, that could

also happen if the stock is a common one and

broader Indian Ocean catches prove

unsustainable. An additional complication is

Striped marlin are a large, migratory billfish

species distributed throughout the Indian and

Pacific oceans. They grow quickly to become

apex predators on a variety of prey, including

fish, squid and crustaceans. Striped marlin are

caught by longline vessels operating off the

east and west coast of Australia, but they are

also an important recreational species. In the

that, in either case, a decline in availability

may be difficult to identify from catch rates

alone. Fishing efficiency probably increased

when larger vessels joined the WTBF fleet

and as fishers gained experience and

developed skills in targeting swordfish.

Changes in the size composition of the catch

might provide an alternative indicator of

stock status, especially since most large

swordfish caught by longline are female and

female swordfish mature at much larger sizes

than males.

A BRS review of swordfish fisheries in

other parts of the world showed that, without

effective controls, fishing effort in swordfish

fisheries often expanded to overshoot the

optimal level. Such experiences suggest that

the WTBF longline fleet has the potential to

overfish swordfish if effort increases

significantly from the current low levels.

S T R I P E D M A R L I N

S T A T U S

Uncertain in the Indian Ocean and the WTBF.


A L B A C O R E T U N A

S T A T U S

Uncertain in the Indian Ocean and the WTBF.

Albacore are a temperate tuna species,

distributed from 5° N to 40° S in the Indian

Ocean, with some mixing with the Atlantic

Ocean likely. They are a highly migratory

species and individuals swim large distances

during their lifetimes. Pre-adults (2–5 years

old) appear to be more migratory than adults.

The maximum age reported for Indian Ocean

albacore is 8 years, whereas Pacific Ocean

albacore have been reported live to at least 10

years. Little is known about the reproductive

biology of albacore in the Indian Ocean but it

appears, based on biological studies and on

fishery data, that the main spawning grounds

are east of Madagascar between 15° S and

25° S during the fourth and first quarters of

each year. Adult albacore spawn in warm

waters (sea surface temperature >25°C). In

the Pacific Ocean, albacore grow relatively

slowly (compared to skipjack and yellowfin)

and become sexually mature at about 5–6

years old.

Albacore tuna are not currently a major

target species in the WTBF. Most of the

albacore catch (98%) is taken by longliners

from Taiwan and Japan operating between

20° S and 40° S, with remaining catches by

purse seine and other gear. Large catches of

juvenile albacore were taken by drifting

gillnets in the southern Indian Ocean (30° S

to 40° S) between 1985 and 1992, total

catches reaching around 30 000 t. Annual

catches declined following the cessation of

drift gillnetting, increased again from 1998 to

2001 (ranging from 37 700 t to 40 600 t), and

then averaged 24 900 t between 2002 to 2006.

Albacore catches of around 3000 t to 5000 t

have been recorded in recent years for a fleet

of fresh-tuna longliners operating from

Indian Ocean they are found north of 40° S,

mainly inhabiting the surface layer to depths

of around 150 m. Early Japanese surveys

provided evidence for separate spawning

grounds in the eastern and western Indian

Ocean, but stock structure is not known and

is a high priority area for research, as are age

validation and growth studies.

Recorded catches varied between 4000 t

and 7000 t for most of the 1990s, but have

been below 3000 t since 2000. Catches are

relatively evenly divided between the eastern

and western Indian Ocean, with vessels from

Taiwan taking most of the catch. However,

purse-seine fleets also take striped marlin as

bycatch, and those catches are poorly

recorded. Furthermore, there have been major

increases in the catch of unidentified billfish

by gillnet fleets operating mainly in the

waters of Sri Lanka, India and Pakistan.

No reliable assessment of striped marlin is

available for the Indian Ocean, and the

stock’s status is uncertain.

The average retained weight of striped

marlin reported in the WTBF logbooks for

the years from 2000 to 2004 was less than 1 t

per year. However, the logbooks also

indicated that large numbers of striped marlin

are not retained by commercial fishers. Data

from the observer program indicate that a

large percentage are alive and vigorous when

retrieved and so have the potential to be

released alive.

Implementation of resource-sharing

arrangements between commercial and

recreational fishers will be important to the

long-term management of the species.


Indonesia. In certain areas, large albacore are

also taken seasonally, often in free-swimming

schools, by the purse-seine fishery.

Assessment of the status of albacore tuna

in the Indian Ocean was attempted in 2004,

but results were inconclusive and stock status

is uncertain. Indicators such as the average

size in the catch and catch rates have not

shown declines in recent years.

Environmental issuesEnvironmental issues in the WTBF include

the catch and release of black and blue

marlin; the catch of sharks; interactions with

seabirds and sea turtles; and discarding and

loss of fishing gear and packaging.

In response to bycatch concerns, AFMA

formulated a bycatch action plan for the three

Commonwealth tuna fisheries (WTBF,

Eastern Tuna and Billfish Fishery and

Southern Bluefin Tuna Fishery). Over 60

marine species have been recorded from AFZ

longline catches, including tuna and tuna-like

fish, billfish, sharks, rays, various other fish,

seabirds, and (rarely) sea turtles and marine

mammals. When Japanese longliners were

operating in the fishery, they retained about

30 species (mainly tunas, billfishes and

sharks) for commercial sale. The bycatch

species (most commonly blue shark, Prionaceglauca) were released or discarded at sea.

The overall impact of fishing on shark

species across the Indian Ocean is poorly

known, so improving the understanding of

shark status is a high priority for the IOTC

Bycatch Working Party. The 2003–07 pilot

scientific monitoring program found that

domestic longliners frequently catch blue

shark and crocodile shark (Pseudocarchariuskamoharai). The latter are quite uncommon in

other longline fisheries.

Commercial markets have developed in

Australia and overseas for several bycatch

species, including escolar or black oilfish

(Lepidocybium flavobrunneum), oilfish

(Ruvettus pretiosus) and mahi mahi

(Coryphaena hippurus). Several other

species, such as wahoo (Acanthocybiumsolandri), have commercial potential.

Offshore Constitutional Settlement

arrangements currently give jurisdiction over

sharks to the Western Australian Government.

WTBF operators are permitted to land a

maximum of 20 sharks per vessel per fishing

trip within the AFZ. A 2001 BRS report

highlighted high levels of shark bycatch and

the widespread practice of ‘shark finning’ in

Australia’s tuna fisheries, particularly in the

Eastern Tuna and Billfish Fishery and the

WTBF. In 2005, the IOTC agreed that the

weight of fins held aboard vessels should not

exceed 5% of the weight of sharks aboard.

Fishery-specific arrangements are required to

increase knowledge about shark catches and

their sustainability. In the interim, AFMA has

banned the practice of finning sharks at sea,

prohibiting the possession or landing of fins

separated from carcasses. AFMA has also

banned wire traces (which increase the

likelihood of retaining shark). In early 2007,

interim arrangements were approved for

permit holders undertaking single-jurisdiction

high-seas trips (that is, trips beyond the AFZ)

to apply to land up to 100 pelagic sharks per

trip (comprising a maximum of 80 blue

sharks and 20 other sharks from an approved

list of eight species). A possible revision of

the Offshore Constitutional Settlement

arrangements is being discussed by the

Australian and Western Australian

governments.

Longline closures north of Hawaii and on

the Grand Banks in the north Atlantic have

been introduced because of public concern

over incidental catches of sea turtles during

swordfish longlining. Catches of turtles have

been reported in WTBF logbooks and during

interviews with operators. The 2003–07 pilot

scientific monitoring program reported low

catch rates of turtles; those captured were

generally being released in a live and

vigorous condition.


Seabirds, such as albatrosses and

shearwaters, are attracted to longline baits

when vessels are setting their gear, and some

birds become hooked and drown. In August

1998, the then Australian Government

Minister for the Environment and Heritage

approved a threat abatement plan to reduce

the incidental catch of seabirds by longliners.

The Eastern Tuna and Billfish Fishery chapter

details progress in identifying longline fishing

practices to reduce the mortality of seabirds.

All WTBF operators are currently required to

carry an approved bird-scaring ‘tori’ line, to

use it, to set their longlines only at night

when operating south of 30° S, and to not

discharge offal during line setting and

hauling. Pilot observer program data

indicated that seabird bycatch rates in the

WTBF were below the threat abatement plan

target of 0.05 birds per 1000 hooks.

Further readingBromhead, D, Pepperell, J, Wise, B &

Findlay, J 2004, Striped marlin: biologyand fisheries, Bureau of Rural Sciences,

Canberra.

Campbell, RA, Tuck, GN, Pepperell, JG &

Larcombe, JWP 1998, Synopsis on thebillfish stocks and fisheries within thewestern AFZ and the Indian Ocean,

Australian Fisheries Management

Authority, Canberra.

Deriso, RB, Bayliff, WH & Webb, NJ 1998,

Proceedings of the first world meeting onbigeye tuna, special report 9, Inter-

American Tropical Tuna Commission, La

Jolla, California.

Dowling, N, Peel, S & Basson, M 2005, Datasummary for the Southern and WesternTuna and Billfish Fishery, CSIRO Marine

Research, Hobart.

Falterman, B, Pepperell, J & Graves, J 2000,

Population genetics and stock structure ofblack marlin (Makaira indica) in thePacific and Indian oceans, report to

Australian Fisheries Management

Authority, Canberra.

Indian Ocean Tuna Commission 2007, Reportof the tenth session of the ScientificCommittee, Indian Ocean Tuna

Commission, Seychelles.

Larcombe, JWP, Caton, A, Williams, DMcB

& Speare, PJ 1997, Western tuna andbillfish fisheries research, Bureau of

Resource Sciences, Canberra.

Rose, C & McLoughlin, K 2001, Review ofshark finning in Australian fisheries, final

report to Fisheries Resources Research

Fund, Bureau of Resource Sciences,

Canberra.

Management performanceBetween 1999 and 2002, the WTBF was

among the fastest growing fisheries in

Australia. A management plan came into

force in October 2005, under which ITQs

rather than input controls will be the principal

management tool. Initial total allowable

commercial catches (TACCs) have been

proposed for bigeye tuna (2000 t), yellowfin

tuna (5000 t), broadbill swordfish (3000 t)

and striped marlin (125 t), in line with the

Australian Government position that as a

coastal state Australia is entitled to a portion

of overall sustainable yields from the Indian

Ocean. However, because of an outstanding

appeal to the Statutory Fishing Rights

Allocation Review Panel, AFMA has not

been able to finally grant SFRs and

implement the management plan. The TACCs

are considerably higher than historical

catches, but under the plan they apply to

high-seas waters as well as the AFZ and are

intended to cover wider expansion of the

fishery into the Indian Ocean. Other species,

both target and non-target, will be monitored

to determine any future need for quota

management. Legislative difficulties have

prevented the implementation of resource-

sharing arrangements that were announced

for the fishery in October 2005. Under the

arrangements, summer and winter closures

would exclude commercial fishers from areas


selected to benefit recreational fishers

targeting prized species (such as marlins).

Commercial catches of longtail tuna in the

WTBF have been limited to 35 t.

Although ITQs have been identified as the

preferred method of control, the limited

amount of data available from the fishery and

the regional extent of the key stocks present

problems for the estimation of scientifically

robust TACCs. Management of the fishery

should be adaptive, and allow for upward or

downward adjustment of TACCs when new

information becomes available. For this

reason, development of a management

strategy with biological reference points and

decision rules has been a major consideration

in the development of the harvest strategy for

the fishery.

The stock structure of the main target

species in the WTBF is poorly known.

Nevertheless, it is clear that WTBF

management must consider the possible level

of interaction with tuna and billfish fisheries

in the broader Indian Ocean. This complicates

the implementation of effective domestic

management for what is a small sector of the

fishery—the approach adopted internationally

may necessitate domestic adjustment of

management arrangements. Furthermore,

management arrangements established for the

WTBF need to comply with the United

Nations Fish Stocks Agreement (1995), which

entered into force on 11 December 2001.

It is highly likely that there is significant

interaction among the major longline fisheries

operating in the eastern Indian Ocean, with

the fleets from Australia, Indonesia, Japan,

South Korea and Taiwan probably exploiting

common stocks of bigeye tuna, yellowfin tuna

and, perhaps, swordfish. Further research is

needed to ascertain whether these are the

same stocks exploited by the purse-seine

fleets of the European Union, which operate

mainly in the tropical western Indian Ocean.

The outcomes of research on the structure of

stocks in the Indian Ocean will affect the

future management of the fishery.

The IOTC has yet to implement effective

management measures for Indian Ocean tuna

fisheries. As early as 1999, its scientific

committee concluded that bigeye tuna were

likely to be fully fished or overfished in the

Indian Ocean. The committee suggested that

the catch of juvenile bigeye tuna by purse-

seiners fishing on FADs had contributed to

the decline in biomass, and that longline and

purse-seine effort should not be increased.

The IOTC requested advice on the impact

that various time and area closures might

have on mortality levels and on the fisheries.

In 2000, the IOTC decided against

introducing FAD-exclusion areas, despite the

likely benefits in reducing juvenile bigeye

tuna mortality. That decision was partly

linked to the effects of such regulations on

the economic viability of the industrial purse-

seine fleet. On the basis of further scientific

evidence, Australia introduced a revised

proposal for a FAD-exclusion area in 2003.

However, the European Union strongly

opposed the proposal and the resolution did

not proceed. In 2004, the IOTC Scientific

Committee reported that catches of bigeye

tuna were higher than sustainable levels. At

the June 2005 meeting of the commission, the

strongest conservation measures to date were

adopted in a resolution to limit future catches

of the species. However, no progress was

made towards implementing catch limits at

the 2006 commission meeting; instead, new

resolutions have been adopted that require

limits on future effort levels. The IOTC will

need to develop appropriate procedures to

ensure implementation of those limits.

Documents

Western Tuna and Billfish Fishery - Attachment 1...Western Tuna and Billfish Fishery 81 fleet’s annual catch ranged up to 125 t of swordfish, 1034 t of bigeye tuna and 1052 t of