Threatened species & ecological communities

Southern Bluefin Tuna (Thunnus maccoyii)

Advice to the Minister for the Environment and Heritage from the Threatened Species Scientific Committee (TSSC) on Amendments to the list of Threatened Species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)
7 September 2005

The Minister for the Environment and Heritage, Senator the Hon Ian Campbell has considered the advice of the Threatened Species Scientific Committee on the Southern Bluefin Tuna and decided not to list the species under the EPBC Act at this time.

The Minister has concluded that the listing of the Southern Bluefin Tuna as a threatened species under the EPBC Act would be detrimental to the survival of the species, as it may weaken Australia's ability to influence both the management of the global fishing effort and the global conservation of the species. As a result, conservation of the Southern Bluefin Tuna in Australian waters could not be achieved.

Contents

1. Scientific name, common name (where appropriate), major taxon group

Thunnus maccoyii (Southern bluefin tuna)

2. Description

The Southern bluefin tuna (SBT) is a large silver-white fish with a blue-black upper body and yellow tinged fins. The bodies of SBT are moderately long and muscular, with small scales covering the skin. Keels are present near the tail and are coloured yellow in juveniles and black in adults. SBT can grow to over 2 metres in length and up to 200 kilograms in weight, however, more commonly, adults tend to be around 1.6 metres in length.

SBT are one of 13 other species of tuna in the Scombridae family and are related to the billfishes, which include swordfish, marlins and spearfish. The species is long lived and slow to mature. Australian scientists believe it matures between 10 and 12 years of age, and it can live for up to forty years. It is also known to be one of the fastest ocean swimmers in the world, and it often travels in speed bursts of up to 70 km/hr while feeding.

SBT tend to school to feed, and are carnivorous, feeding mainly on fish, squid, krill and salps. In offshore waters, they also eat small crustaceans and larger fish. SBT are opportunistic and considered a top-level predator in the marine environment.

The SBT is listed as threatened under the Victorian Flora and Fauna Guarantee Act 1988 and as endangered under the NSW Fisheries Management Act 1994.

3. National context

The SBT is a slow growing, highly migratory species, forming a single widely distributed population in the southern oceans, but with a single known spawning ground in the Indian Ocean, between Java and northern Western Australia. In Australian waters, SBT range from northern Western Australia, around the southern region of the continent, to northern New South Wales. The southernmost portion of the spawning ground lies within Australia's Exclusive Economic Zone. It is not known whether all mature SBT spawn each year, every few years or even only once in their lifetime, but a single female can release up to 15 million eggs during a spawning period.

Juvenile SBT tend to move south from the spawning ground to the south west of Australia in their first years of life. The warm Leeuwin Current which begins near the spawning ground and is strongest in April, right after the spawning period, helps sweep the SBT down the West Australian coast to the Great Australian Bight and beyond.

Surface schooling juveniles are associated seasonally with the continental shelf region of the Great Australian Bight, but it is not known what fraction of the juvenile stock is present. SBT continue to live off southern and south eastern Australia until six to nine years of age. By maturity, most fish have dispersed into the deeper waters of the south Atlantic, Indian and south west Pacific Oceans. SBT are also known to disperse to waters off South Africa, however the proportion of the population that undergo this migration is unknown.

The single widely distributed population of SBT occurs around the globe in waters between 30°S and 50°S, though the species is mainly found in the eastern Indian Ocean and in the south western Pacific Ocean.

BRS Fishery Status Reports

The Bureau of Rural Sciences' (BRS) Fishery Status Reports review the status of fish stocks managed by the Australian Government, and describe trends in the status. The reports contribute to the evaluation of Australian Government fisheries management and are based on the most recent assessments carried out by research bodies including State and Territory agencies, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and BRS. Information is also gathered from unpublished reports from fishery assessment meetings and workshops organised by AFMA and other agencies with involvement in fisheries research, such as the Fisheries Research and Development Corporation (FRDC).

Through the Fishery Status Reports, BRS aims to make fishery status and trends information available to government, industry and the community. The reports, first published in 1992, provide a means to monitor whether strategies are succeeding in sustaining the resources on which each fishery is based.

The BRS Reports (from 1992 to 2004) are used in this advice to assess the current conservation status of SBT against the threatened species listing criteria of the EPBC Act. These reports are publicly available. In the Committee's judgement the BRS syntheses are the best information available, and these assessments have been used because they provide information on the status of the species that has been consistently assessed, and is comparable from year to year.

4. How judged by TSSC in relation to the EPBC Act criteria.

TSSC judges the species to be eligible for listing under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - It has undergone, is suspected to have undergone or is likely to undergo in the immediate future a very severe, severe or substantial reduction in numbers

The use of the term 'a reduction in numbers' is not appropriate when estimating a decline in a high fecundity fish, like SBT. This is because the total number of individuals in the SBT population includes the large number of larval fish produced each year. By comparison, the number of adult fish is minuscule. Therefore, for high fecundity fish, like SBT, some definition of population other than total number of individuals is necessary to understand the current conservation status of the species.

Since the early 1980s, rather than focussing on total numbers or population size, scientific advice on the management of SBT has generally been based on trends in the estimated parental biomass or spawning biomass (total weight of mature fish in the population) and on estimated recruitment (number of fish at age 1 entering the population each year).

Data Collection

In the Australian commercial fishery, the primary means of collecting SBT 'fishery dependent data' is through the range of logbooks and associated catch records that are required by law and which are used by the Australian Fisheries Management Authority (AFMA) for monitoring, compliance and research. In addition, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) obtains trade information from all members of the CCSBT through a Trade Information System, although it is recognised that this is limited as it quantifies only the fish imported into Japan, the main market for the species. It does not encompass the large component of the global catch landed in Japan by Japanese longliners.

The collection of SBT 'fishery independent data' is progressed primarily through the Scientific Research Program (SRP) established under the auspices of the CCSBT. This involves a range of scientific studies specifically designed to collect information pertinent to the assessment of the stock of SBT. Within Australia, CSIRO and BRS are the primary research organisations responsible for SBT research and undertake a wide range of projects involving stock modelling and assessments, migration, biology and aquaculture. BRS is responsible for compiling the results of this research and producing an annual assessment of the status of the stocks.

Recreational take of SBT

There is no reliable estimate of the recreational take of SBT in Australian waters. BRS is currently collecting data on recreational take and this information is expected to be available after the CCSBT Scientific Committee meeting in October 2005.

International context

In May 1994, the Convention for the Conservation of Southern Bluefin Tuna (the Convention) came into force. The CCSBT was formed as a management body to fulfil the aims of the Convention. One of the primary activities of CCSBT is to set a total allowable catch (TAC) and to allocate that catch between member nations. The global catch includes allocations for artisanal (subsistence) and recreational take and mortalities attributable to research.

SBT is fished by many nations, with Japan, Australia, New Zealand, the Republic of Korea, Taiwan and Indonesia identified as the major nations taking SBT commercially. However, there are a number of other nations with developing fisheries, such as South Africa, China, the European Union (particularly Spain) and the Philippines, with aspirations for catch allocation within the CCSBT.

Since the late 1950s, SBT has been heavily fished (see Figure 1), with the annual global catch peaking at 80 000 tonnes in the early 1960s. As concern for the status of SBT grew, global catch limits were progressively reduced from around 40 000 tonnes in 1984 at the start of the informal management arrangement to 11,750 tonnes in 1990.

When the Convention came into force, CCSBT set a TAC of 11 750 tonnes, with national allocations of 6065 tonnes, 5265 tonnes and 420 tonnes to Japan, Australia and New Zealand respectively. For the period 1997 to 2003, CCSBT was unable to agree on a TAC or national quotas, and in the absence of a decision by CCSBT to set a TAC, Australia and New Zealand maintained their catches at the pre-agreed levels. However, Japan sought a quota increase, either as an additional commercial catch, or an 'experimental fishing program' (EFP), or a combination of these. Australia and New Zealand opposed any increase, and no agreement was reached despite numerous and extensive meetings. In 1998, Japan undertook an EFP without CCSBT endorsement, and increased its total catch to 7052 tonnes. In 1999, Japan again proceeded unilaterally to increase its quota through an EFP, and increased its total catch of 7552 tonnes. Australia subsequently took legal action against Japan through the international legal system including the International Tribunal on the Law of the Sea (ITLOS) to have this 'overcatch' repaid.

In 2003-04, and for the first time since 1997, a global TAC of 14 930 tonnes was agreed (composing 14 030 tonnes for members of CCSBT and 900 tonnes for co-operating non-members).

Figure 1: Global Catch of Southern bluefin tuna (BRS, 2004)

Figure 1: Global Catch of Southern bluefin tuna (BRS, 2004)

Fig 1: Global catch data for SBT from 1952 through to 2003. Vessels fishing under six flags - Australia, Japan, Indonesia, Fishing Entity of Taiwan, Korea and New Zealand have historically taken significant quantities of SBT. However, Australia and Japan have always been the major catching nations. The global catch of SBT peaked in 1961 at 81 605t. Since 1990 it has ranged between 13 231t (1994) and 19 588t (1999). The annual Australian catch of SBT peaked in 1982 at 21 501t. Since the 1989-90 season, it has been below 5265t, which is Australia's long-standing national allocation by the Commission for the Conservation of Southern Bluefin Tuna (CCSBT).

Australian context

The assessment of the conservation status of SBT within the Australian jurisdiction cannot be meaningfully separated from an assessment of the global situation. All available evidence indicates that SBT is a single stock or population, and hence there is not what could be meaningfully considered an Australian population. There is only one spawning ground and genetic studies have not revealed any consistent or significant genetic differences between fish found in Australian waters, other Exclusive Economic Zones (EEZs) or the 'high seas'. Further, there is no evidence that any significant component of the SBT stock is restricted for all or most of its life to Australian waters.

In Australia, the species is regarded by the BRS (BRS, 2004) as severely recruitment-overfished 1, with spawning biomass in the order of 3 to 14% of the estimated 1960 level (its unfished size) or 14 to 59% of the estimated 1980 (target 2) level, the recruitment-overfishing reference limit adopted by CCSBT (Basson et al 2004).

Within the Australian SBT Fishery, BRS has classified SBT as being 'overfished' every year since the first BRS fishery status report was produced in 1992. 'Overfished' is a term used to describe a fish stock in which the amount of fishing is excessive; or for which the catch depletes the biomass too much; or a stock that still reflects the effects of previous excessive fishing.

Stock Assessment

CSIRO conducted an in depth assessment of the SBT stock in 2004 (Basson et al 2004). This assessment indicated a relatively continuous decline in the SBT spawning stock since the inception of the SBT fishery. However, the large catch cuts in the mid-1980s appeared to have arrested the rate of decline. Since the late 1990s, it is uncertain whether the spawning stock is continuing to slowly decline, remaining essentially unchanged or beginning to increase.

The results of this assessment, along with assessments conducted by Japan, were reviewed by the CCSBT Scientific Committee and its Stock Assessment Group, which includes a panel of external independent experts in fishery stock assessments, in September 2004 (CCSBT, 2004b, c). The overall consensus conclusions of the CCSBT Scientific Committee were essentially the same as those of the CSIRO assessment:

'At the time of the most recent round of quota reductions (1988), spawning stock size was well below levels in 1980 with trends since the late 1990s either upward or slightly downward with a slight upward trend more likely.'

Notwithstanding these assessments, that suggest the parental biomass of SBT has been stable over the past decade with a slight increase in the period 2000-2003 (CCSBT, 2004c), relative to 1960, CSIRO's assessment estimates that current spawning biomass is between 3 to 14% of the 1960 level. CSIRO's assessment estimates that current spawning biomass is between 14 to 59% of the 1980 level (Basson et al 2004).

Future trends

Despite widespread agreement regarding the historical decline of SBT spawning biomass, there is major disagreement among scientists about the most likely longer-term trend of the spawning biomass.

Stock projections are regularly performed as part of the SBT stock assessment process, and are conducted by the CCSBT Scientific Committee. They are an integral part of the CCSBT Management Procedure evaluation process, and provide indications of the prospect of recovery under a range of alternative catch scenarios. Even at current catch levels, some models show a rapid recovery of the stock over the next 30 years whereas others show extinction even at zero catch levels.

Projections of future biomass levels are highly variable, depending on the variables used. The CCSBT Scientific Committee meeting in October 2004 reported 'Given all the evidence, the probability of further stock decline under current catch levels is now judged to be greater than in 2001, when an increase or decline under current catches were considered equally likely.'

Overall, there appears to be a very low chance that the current CCSBT recovery objective will be met at current catch levels, and even if global catches were reduced to zero, the recovery objective may not be met.

The Committee is concerned about the threat to SBT from fishing in its single, relatively restricted spawning ground in the Indian Ocean, between Java and northern Western Australia. The ongoing loss of mature individuals from the spawning population is likely to impact on the abundance of the species both globally and within the Australian jurisdiction.

In addition, the Committee notes the progressive changes in the distribution of juveniles, including the loss of schools of juvenile fish along the NSW coast of Australia since the 1980s, which indicates there has been a reduction in the geographic distribution of the species and supports a conclusion that an overall decrease in the abundance of the species has occurred.

Conclusion

Australia and the CCSBT Scientific Committee have consistently agreed that the SBT parental biomass is at historically low levels. Trends in estimates of SBT parental biomass exhibit a long and continuous decline as a consequence of intensive fishing of the SBT stock since the late 1950s. In 2004, CSIRO estimated the current spawning biomass to be in the order of 3 to 14% of that which existed in 1960 (Basson et al 2004).

In the 1980s, management action resulted in large reductions in the SBT catch. This slowed the decline of the parental biomass in the early 1990s. It is uncertain whether the spawning stock is continuing to slowly decline since the late 1990s, remaining essentially unchanged or beginning to slowly increase.

Notwithstanding the recent trends in parental biomass, CSIRO (Basson et al 2004) has estimated that the parental biomass is currently in the order of 3 to 14% of that in 1960 (and in the order of 14 to 59% of the 1980 level). According to Caton (1996) a Southern bluefin tuna generation (generation length) is about 10 to 18 years. Two generations would involve 20 to 35 years, and three generations would be 30 to 54 years. Therefore, using the 1980 figures, there has been a conservative decline of between 41 and 86% of the SBT parental biomass within three generations of the species.

Therefore, the species is eligible for listing as endangered under this criterion.

Criterion 2 - Its geographic distribution is precarious for the survival of the species and is very restricted, restricted or limited

The SBT is a highly migratory species, forming a single widely distributed population in the southern oceans, particularly in the Southern Ocean and the Indian Ocean, and with a single spawning ground in the Indian Ocean, between Java and northern Western Australia. The single population of SBT is distributed around the globe in waters between 30°S and 50°S.

In Australian waters, SBT range from northern New South Wales, around the southern region of the continent, to northern Western Australia.

Notwithstanding SBT's single, relatively restricted spawning ground in the Indian Ocean being subject to threats from fishing (see discussion under Criterion 1), SBT is a species with a wide geographic distribution.

Therefore, the geographic distribution of SBT is not precarious for the survival of the species and the species is not eligible for listing under this criterion.

Criterion 3 - The estimated total number of mature individuals is very low, low or limited and: (a) evidence suggests that the number will continue to decline at a particular rate; or (b) the number is likely to continue to decline and its geographic distribution is precarious for its survival

As indicated in the discussion under Criterion 1, despite there being widespread agreement among scientists regarding the historical decline of SBT spawning biomass, there is major disagreement about the most likely longer-term trend of spawning biomass. For example, even at current catch levels, some stock projections show a rapid recovery of the stock over the next 30 years whereas other projections show extinction even at zero catch levels.

Therefore, it is not possible to conclude that numbers of SBT will continue to decline at a particular rate, nor is it considered that the geographic distribution of SBT is precarious for the survival of the species.

Therefore, the species is not eligible for listing under this criterion.

Criterion 4 - The estimated total number of mature individuals is extremely low, very low or low

There is widespread agreement between the scientific authorities of CCSBT member countries that the parental biomass of SBT is a fraction of the 1960 level. The 2004 CCSBT meeting concluded that 'the current assessments suggest the SBT spawning biomass is at a low fraction of its original biomass and well below the 1980 biomass.' Relative to 1960, CSIRO's assessment results estimate that current spawning biomass is between 3 and 14%, and 14 and 59% of the 1980 level (Basson et al 2004).

In addition, BRS has classified SBT as being 'overfished' every year since the first BRS fishery status reports were first produced in 1992.

However, while the parental biomass may be considered to be very low compared to the 1960 level (its unfished size) and the 1980 level (the CCSBT target level), this information cannot be used to determine the total number of mature individuals of the species.

Therefore, the species is not eligible for listing under this criterion.

Criterion 5 - Probability of extinction in the wild

All assessments of the SBT stock indicate that catches of SBT are the primary factor that have caused the decline of the stock to its current low level and which has prevented the recovery of the stock.

However, it is difficult to assess whether fishing has the potential to cause the biological extinction of the species. Given the nature of targeting in some components of the international fishery and the fact that SBT is taken primarily as bycatch in some components of the fishery, there is potential for continued fishing mortality even at very low levels of SBT abundance. Whether this would be sufficient to cause extinction of the species is uncertain.

The effects of fishing on the SBT stock could potentially be compounded by environmental changes affecting recruitment or survival. Of particular concern, given the current low stock of SBT, is the risk that a combination of factors including:

could combine to cause an abrupt recruitment decline and a subsequent further decline in the spawning biomass. However, it is not possible to quantify the probability of this event occurring.

There are insufficient quantitative data available to assess this species against this criterion.

5. Conclusion

SBT continues to be overfished despite the international management arrangements which have been formally in place since 1994.

The parental biomass is currently in the order of 3 to 14% of that in 1960 (its unfished size). In addition, BRS has classified SBT as being 'overfished' every year since the first BRS fishery status reports were first produced in 1992.

Stock assessment models have shown a significant historic decline in the biomass of SBT. The mature population of SBT has declined significantly over its last three generations (since the 1980s) and is currently at a very low level.

Therefore, the species is eligible for listing as endangered under Criterion 1.

6. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by including in the endangered category:

The Committee notes the importance of Australia's leadership within CCSBT to achieve long-term conservation outcomes for the SBT. In particular, the Committee recognises the need for international co-operation to address fishing impacts on the species' spawning ground. The Committee is concerned that the listing of SBT under the EPBC Act at this time may be detrimental to the survival of the species, as it may weaken Australia's ability to influence the global conservation of the species, and by implication, its conservation in Australian waters.

The Minister for the Environment and Heritage, Senator the Hon Ian Campbell has considered the advice of the Threatened Species Scientific Committee on the Southern Bluefin Tuna and decided not to list the species under the EPBC Act at this time.

The Minister has concluded that the listing of the Southern Bluefin Tuna as a threatened species under the EPBC Act would be detrimental to the survival of the species, as it may weaken Australia's ability to influence both the management of the global fishing effort and the global conservation of the species. As a result, conservation of the Southern Bluefin Tuna in Australian waters could not be achieved.

Publications used to assess the nomination

ABARE (Australian Bureau of Agricultural and Resource Economics), 'Southern Bluefin Tuna and CITES - An Economic Perspective' Canberra, 1999.

AFMA, 2002. 'Draft Assessment Report - Southern Bluefin Tuna' Australian Fisheries Management Authority, Canberra, July 2002.

AFMA, 2003. Explanatory Notes for further proposed amendments (July 2003) to the SBT Fishery Management Plan. Australian Fisheries Management Authority, July 2003.

Basson M, Kolody D, Polacheck T, Preece A and Hartog J, 2004. Assessment and projections of SBT stock assessment and summary of agreed stock status reference points. CCSBT-ESC/0904/23.

BRS, 1998. 'BRS Comments on the nomination of SBT as a vulnerable species' Bureau of Rural Sciences, Canberra, May 1998.

BRS, 2001. Fishery Status Reports 2001. Bureau of Rural Sciences, Canberra, ACT, 2001.

BRS, 2002. Fishery Status Reports 2002-2003 - Southern Bluefin Tuna Chapter. Bureau of Rural Sciences, Canberra, ACT, 2002-2003.

BRS, 2004. Fishery Status Reports 2004. Edited by Albert Caton and Kevin McLoughlin. Bureau of Rural Sciences, Canberra, ACT, 2004.

Caton A E, 1991. 'Review of aspects of SBT Biology, Population and Fisheries' Bureau of Rural Sciences, Canberra, ACT, 1991.

Caton A, 1996. 'Characteristics of southern bluefin tuna relative to CITES Appendices criteria: A review for the Australian Nature Conservation Authority, Canberra. From BRS, 1998. 'BRS Comments on the nomination of SBT as a vulnerable species' Bureau of Rural Sciences, Canberra, May 1998.

CCSBT, 2003a. 'Report of the Tenth Annual Meeting of the Commission' Commission for the Conservation of Southern Bluefin Tuna, 7-10 October 2003, Christchurch, New Zealand.

CCSBT, 2003b. 'Report of the Eighth Meeting of the Scientific Committee' Commission for the Conservation of Southern Bluefin Tuna, 1-4 September 2003, Christchurch, New Zealand.

CCSBT, 2003c. 'Report of the Fourth Meeting of the Stock Assessment Group' Commission for the Conservation of Southern Bluefin Tuna, 25-29 August 2003, Christchurch, New Zealand.

CCSBT, 2004a. 'Report of the Eleventh Annual Meeting of the Commission' Commission for the Conservation of Southern Bluefin Tuna, 19-22 October 2004, Busan, Republic of Korea.

CCSBT, 2004b. 'Report of the Ninth Meeting of the Scientific Committee' Commission for the Conservation of Southern Bluefin Tuna, 13-16 September 2004, Seogwipo City, Jeju, Republic of Korea.

CCSBT, 2004c. 'Report of the Fifth Meeting of the Stock Assessment Group' Commission for the Conservation of Southern Bluefin Tuna, 6-11 September 2004, Seogwipo City, Jeju, Republic of Korea.

CSIRO, 1996. 'Characteristics of SBT relative to CITES Appendices Criteria - A review compiled by CSIRO and BRS for the Australian Nature Conservation Authority' Canberra, 1996.

CSIRO, 2001. 'An Intergrated Staisitical Time Series Assessment of the SBT Stock based on Catch at Age Data' CSIRO Marine Research, August 2001.

CSIRO, 2002. 'Commercial Aerial Spotting for SBT in the Great Australian Bight by Fishing Season 1982-2000' CSIRO Marine Research Report R99/1498, April 2002.

Kearney, Bob, Foran, Barney, Poldy, Franzi, Lowe, Don, 2003. 'Modelling Australia's Fisheries to 2050: Policy and Management Implications' Fisheries Research and Development Corporation, Canberra, March 2003.

Footnotes

1. Recruitment overfishing is fishing above the level at which the recruitment to the exploitable stock becomes significantly reduced. This is characterized by a reduced spawning stock, a decreasing proportion of older fish in the catch, and generally low recruitment year after year.
2. The CCSBT's rebuilding objective or target is to rebuild parental biomass to 1980 levels by 2020.