Western Tuna and Billfish Fishery

​​Chapter 24: Western Tuna and Billfish Fishery

A Williams, H Patterson and A Bath

Figure 24.1 Area of the Western Tuna and Billfish Fishery, 2017
TABLE 24.1 Status of the Western Tuna and Billfish Fishery
Status20162017Comments
Biological status a Fishing mortality BiomassFishing mortalityBiomass 
Striped marlin (Kajikia audax)Subject to overfishingNot overfishedSubject to overfishingUncertainMost recent estimates of biomass from multiple models range above and below the default Commonwealth limit reference point. Current fishing mortality rate exceeds that required to produce MSY.
Swordfish
(Xiphias gladius)
Not subject to overfishingNot overfishedNot subject to overfishingNot overfishedMost recent estimate of spawning biomass is above the default Commonwealth limit reference point. Current fishing mortality rate is below that required to produce MSY.
Albacore
(Thunnus alalunga)
Not subject to overfishingNot overfishedNot subject to overfishingNot overfishedMost recent estimate of spawning biomass is above the default Commonwealth limit reference point. Current fishing mortality rate is below that required to produce MSY.
Bigeye tuna
(Thunnus obesus)
Not subject to overfishingNot overfishedNot subject to overfishingNot overfishedMost recent estimate of spawning biomass is above the default Commonwealth limit reference point. Current fishing mortality rate is below that required to produce MSY.
Yellowfin tuna
(Thunnus albacares)
Subject to overfishingNot overfishedSubject to overfishingNot overfishedMost recent estimate of spawning biomass is above the default Commonwealth limit reference point. Current fishing mortality rate exceeds that required to produce MSY.
Economic statusParticipation rate was low and latency remained high in 2017, suggesting little economic incentives to fish and relatively small NER.

a Ocean-wide assessments and the default limit reference points from the Commonwealth Fisheries Harvest Strategy Policy (DAFF 2007) are used as the basis for status determination.
Notes: MSY Maximum sustainable yield. NER Net economic returns. TACC Total allowable commercial catch.

[expand all]

24.1 Description of the fishery

Area fished

The Western Tuna and Billfish Fishery (WTBF) operates in Australia’s Exclusive Economic Zone and high seas of the Indian Ocean (Figure 24.1). In recent years, effort has concentrated off south-west Western Australia and South Australia. Domestic management arrangements for the WTBF reflect Australia’s commitment to the Indian Ocean Tuna Commission (IOTC; see Chapter 20).

Fishing methods and key species

Key species in the WTBF are bigeye tuna (Thunnus obesus)yellowfin tuna (T. albacares), striped marlin (Kajikia audax)and swordfish (Xiphias gladius)Some albacore (Thunnus alalunga) is also taken.Fishing in the WTBF mainly uses pelagic longline; some minor-line fishing also occurs (Table 24.2).

Management methods

The management plan for the fishery began in 2005, although the Australian Fisheries Management Authority (AFMA) first granted statutory fishing rights in 2010. Under the management plan, output controls have been implemented in the fishery through individual transferable quotas (ITQs) for the four key commercial species (excluding striped marlin) (Table 24.2). Determinations of total allowable commercial catch (TACC) are made in accordance with Australia’s domestic policies, and apply to the Australian Fishing Zone and the high-seas area of the IOTC area of competence. A harvest strategy framework has been developed for the WTBF (Davies et al. 2008), with the intention that it be implemented if fishing effort increases in the fishery and sufficient data are available for use in the strategy. The framework includes a decision tree that defines rules and subsequent adjustments to the recommended biological catch (or level of fishing mortality) in response to standardised size-based catch rates.

The default limit reference points in the Commonwealth Fisheries Harvest Strategy Policy (DAFF 2007) are used to determine stock status in the WTBF. The limit reference point for biomass is 20 per cent of the unfished biomass (0.2B0). For fishing mortality, the limit reference point is the fishing mortality that would achieve maximum sustainable yield (FMSY). The IOTC determines stock status relative to target reference points, not limit reference points, resulting in a different stock status reported by the IOTC for some stocks.

As of 1 July 2015, electronic monitoring (e-monitoring) was made mandatory for all full-time pelagic longline vessels in the Eastern Tuna and Billfish Fishery and the WTBF. At least 10 per cent of video footage of all hauls is reviewed to verify the accuracy of logbooks, which are required to be completed for 100 per cent of shots.

Fishing effort

Effort in the WTBF was relatively low (<20 vessels) from the mid 1980s to the mid 1990s (Figure 24.2). Effort increased in the late 1990s, peaking at 50 active vessels in 2000, but then declined rapidly. Since 2005, fewer than five vessels have been active in the fishery each year.

Figure 24.2 Longline fishing effort, boat statutory fishing rights and active vessels in the WTBF, 1986–2017
Note: SFR Statutory fishing rights.
Source: Australian Fisheries Management Authority

Catch

Swordfish is the main target species in the WTBF, with annual catches peaking at more than 2,000 t in 2001 (Figure 24.3) and declining to a few hundred tonnes in recent years. Bigeye and yellowfin tuna are also valuable target species, although catches of these species have never been as high as for swordfish and have been more variable.

Figure 24.3 Total annual catch, by species, in the WTBF, 1986–2017
Source: AFMA
TABLE 24.2 Main features and statistics for the WTBF
Fishery statistics a20162017
StockTACC
(t)
Catch
(t)
Value

(2015–16)

TACC
(t)
Catch
(t)
Value

(2016–17)

Striped marlin1251Confidential1251Confidential
Swordfish3,000147Confidential3,000166Confidential
Albacore23Confidential16Confidential
Bigeye tuna2,00075Confidential2,00067Confidential
Yellowfin tuna5,00074Confidential5,00072Confidential
Total10,125320Confidential10,125322Confidential
Fishery-level statistics
EffortPelagic longline: 352,274 hooks

Minor line: na

Pelagic longline: 417,997 hooks

Minor line: na

Fishing permits95 boat SFRs95 boat SFRs
Active vesselsPelagic longline: 2

Minor line: 1

Pelagic longline: 3

Minor line: 1

Observer coverage10.2% b11.7% b
Fishing methodsPelagic longline (monofilament mainline), minor line (handline, rod and reel, troll and poling), purse seine
Primary landing portsFremantle and Geraldton (Western Australia)
Management methodsInput controls: limited entry, gear and area restrictions

Output controls: TACCs, ITQs, byproduct restrictions

Primary marketsInternational: Japan, United States—fresh, frozen

Domestic: fresh, frozen

Management planWestern Tuna and Billfish Management Plan 2005 (amended 2016); SFRs issued 2010

a Fishery statistics are provided by calendar year to align with international reporting requirements. Value statistics are by financial year and are in 2015–16 dollars. b As of 1 July 2015, e-monitoring was made mandatory for all full-time pelagic longline vessels in the WTBF. At least 10% of video footage of all hauls are reviewed to verify the accuracy of logbooks, which are required to be completed for 100% of shots.
Notes: ITQ Individual transferable quota. na Not available. SFR Statutory fishing right. TACC Total allowable commercial catch. – Not applicable.

24.2 Biological status

Striped marlin (Kajikia audax)

Striped marlin (Kajikia audax) 

Line drawing: FAO

Stock structure

Mamoozadeh, McDowell & Graves (2017) provided a preliminary assessment of the genetic stock structure of striped marlin throughout the Pacific and Indian oceans using single nucleotide polymorphism molecular markers. Results from the analysis of 29 individual fish suggested that striped marlin in the Indian Ocean represents a genetic stock distinct from those in the Pacific Ocean. There was no evidence for stock structure within the Indian Ocean, but only nine individuals were included in the analysis for the Indian Ocean. Based on these preliminary results, and the lack of evidence to support separate stocks, striped marlin is considered to be a single distinct biological stock for assessments in the Indian Ocean.

Catch history

Catches of striped marlin in the WTBF have been relatively low (<50 t) since the mid 1980s and very low (<5 t) in recent years, with 1 t taken in 2016 and 2017 (Figure 24.4). Total international catches in the IOTC area of competence declined from around 6,000 t in 1995 to around 2,000 t in 2009 (Figure 24.5). Annual catches have increased since 2009, reaching 5,189 t in 2016, which is within the range estimate of MSY from the four stock assessment models (3,264–5,400 t; Table 24.3).

Figure 24.4 Striped marlin catch and TACC in the WTBF, 1983–2017
Note: TACC Total allowable commercial catch; initial TACC for 19 months.
Source: AFMA
Figure 24.5 Striped marlin catch in the IOTC area, 1970–2016
Note: IOTC Indian Ocean Tuna Commission.
Source: IOTC
Stock assessment

Four assessment models were used to assess the Indian Ocean stock of striped marlin in 2017: a stock reduction analysis (SRA), a stock production model incorporating covariates (ASPIC), a Bayesian surplus production model (BSP) and Stock Synthesis 3 (SS3) (Table 24.3). The SS3 model is a fully integrated model that accounts for spatial, length, age and sex structure, whereas the SRA, ASPIC and BSP models are simpler biomass dynamic models that do not. The SRA, ASPIC and BSP models provided estimates of total biomass (B), and SS3 provided estimates of spawning biomass (SB). The median estimates of the 2015 total biomass were 9–32 per cent of unfished (1950) levels using the SRA, ASPIC and BSP models (B2015/B1950 = 0.09–0.32), and the median estimate of the 2015 spawning biomass using SS3 was 6 per cent of unfished (1950) levels (SB2015/SB1950 = 0.06) (Table 24.3). These estimates were all below the level that would support MSY. The median point estimates of fishing mortality from all four models were above the level that would result in MSY (F2015/FMSY = 1.32–3.40). Results from all four models were used to provide management advice to the IOTC (IOTC 2017).

Numerous sources of uncertainty make it difficult to interpret clearly the outputs from the stock assessments for striped marlin. There was uncertainty in the catch data for striped marlin in the Indian Ocean due to non-reporting by some fleets, reporting of striped marlin in an aggregate billfish species group, and conflicting reports from different data sources indicating potentially much larger catches than initially reported by some fleets. Therefore, a large proportion of striped marlin catch data (41 per cent in 2016) is estimated by the IOTC Secretariat. There were large data conflicts among the time series of standardised catch-per-unit-effort (CPUE) and catch data (and length data for SS3) used for the assessments. Standardised CPUE data from the coastal gillnet fisheries, which report the largest catches of striped marlin, were not used in any of the assessment models. For the SS3 model, no length data were available from the coastal gillnet fisheries to estimate selectivity for this fleet, and all the biological parameters used—including growth, maturity, steepness and mortality—were sourced from the Pacific Ocean.

Stock status determination

The numerous sources of uncertainty in assessments, and the range of assessment outputs, lead to significant uncertainty in the status of the striped marlin stock. It is likely that the stock has been heavily depleted, but it is not possible to determine whether the stock is currently above or below the biomass limit reference point (0.2B0). As a result, the Indian Ocean striped marlin stock is classified as uncertain.Despite large uncertainty, fishing mortality was above FMSY for all assessment models, so the stock is classified as subject to overfishing.

Table 24.3. Summary of assessment outputs from four stock assessment models, and ranges (where available), used to assess Indian Ocean striped marlin in 2017
Stock assessment modelMSY (t)B/B1950SB/SB1950B/BMSYSB/SBMSYF/FMSY
SRA3,264
(2,542–4,051)
0.22
(0.08–0.40)
na0.44 (0.17–0.79)na3.04 (1.51–9.16)
ASPIC5,400 (4,863–6,171)0.32na0.62 (0.06–1.18)na1.32 (0.69–5.18)
BSP5,352
(4,330–6,890)
0.09 (0.06–0.13)na0.24 (0.16–0.35)na3.40 (2.45–4.75)
SS34,960 (4,762–5,157)na0.06
(0.04–0.08)
na0.37

(0.25–0.48)

2.43 (1.63–3.23)

Note: B Biomass. F Fishing mortality. MSY Maximum sustainable yield. na Not available. SB Spawning biomass.

Yellowfin tuna
Georgia Langdon, AFMA

Swordfish (Xiphias gladius)

Swordfish (Xiphias gladius) 

Line drawing: Gavin Ryan

Stock structure

Swordfish in the Indian Ocean is considered to be a single distinct biological stock. The possibility of a separate south-west Indian Ocean stock was examined in the Indian Ocean Swordfish Stock Structure project—a genetic study focused on the links between the south-west and other regions. The study found that genetic markers were consistent with a single stock in the Indian Ocean (Muths et al. 2013).

Catch history

Annual swordfish catch in the WTBF peaked at around 2,000 t in the early 2000s but has declined to below 350 t since 2005. In 2017, the annual catch was 166 t, a slight increase from 2016 (Figure 24.6). Total international catches of swordfish in the IOTC area of competence peaked in 2004 at more than 40,000 t, but declined to around 24,000 t in 2008 (Figure 24.7), likely as a result of the impacts of piracy in the western Indian Ocean. Annual catches in the IOTC area of competence have increased since 2009, reaching 31,407 t in 2016, which is near the 2017 estimate of MSY (31,590 t). However, there is uncertainty in the catch estimates from the Indonesian longline fleet, and an alternative catch history provided a total catch estimate of 39,774 t for 2016, which is above the 2017 estimate of MSY (IOTC 2017).

Figure 24.6 Swordfish catch and TACC in the WTBF, 1983–2017
Note: TACC Total allowable commercial catch; initial TACC for 19 months.
Source: Australian Fisheries Management Authority
Figure 24.7 Swordfish catch in the IOTC area, 1970–2016
Note: IOTC Indian Ocean Tuna Commission.
Source: IOTC
Stock assessment

In 2017, the Indian Ocean swordfish assessment was updated using SS3 with data up to 2015 (IOTC 2017). The SS3 model was spatially disaggregated, sex explicit and age structured. The 2015 spawning biomass for the Indian Ocean–wide stock was estimated to be 31 per cent of unfished (1950) biomass (SB2015/SB1950 = 0.31; range 0.26–0.43) and above the level that supports MSY (SB2015/SBMSY = 1.50; 80 per cent confidence interval [CI] 1.05–2.45) (IOTC 2017). Fishing mortality was estimated to be below FMSY (F2015/FMSY = 0.76; 80 per cent CI 0.41–1.04).

Stock status determination

Assessments of the ocean-wide stock indicate that swordfish biomass is above the default limit reference point (0.2B0) and that fishing mortality is below FMSY. As a result, the stock is classified as not overfished and not subject to overfishing.

Albacore (Thunnus alalunga)

Albacore (Thunnus alalunga) 

Line drawing: FAO

Stock structure

The stock structure of albacore in the Indian Ocean is uncertain, but the species is assumed to be a single biological stock for assessments. A global genetics study of albacore found that the Atlantic Ocean and Indian Ocean populations were not genetically distinguishable, and found no evidence of genetic heterogeneity within the Indian Ocean (Montes et al. 2012). However, the study was based on relatively small sample sizes, and samples were not collected across the entire distribution of albacore in the Indian Ocean. Two distinct stocks of albacore occur in the Atlantic and Pacific oceans, associated with distinct northern and southern ocean gyres. There is no northern gyre in the Indian Ocean, supporting the assumption of a single Indian Ocean albacore stock (IOTC 2014).

Catch history

Historically, albacore catches in the WTBF have been low, peaking at 115 t in 1994 and again at 94 t in 2001 (Figure 24.8). Since 2004, annual catches have been below 30 t. Total international catches in the IOTC area of competence peaked at more than 43,000 t in 2010, and have fluctuated between 30,000 t and 41,000 t since 2011 (Figure 24.9). The average annual catch during the past six years (2011–2016) was approximately 35,000 t, which is lower than the 2016 estimate of MSY (38,800 t) (IOTC 2017).

Figure 24.8 Albacore catch in the WTBF, 1983–2017
Source: Australian Fisheries Management Authority
Figure 24.9 Albacore catch in the IOTC area, 1970–2016
Note: IOTC Indian Ocean Tuna Commission.
Source: IOTC
Stock assessment

In 2016, five assessment models were used to assess the Indian Ocean albacore stock: SS3, ASPIC, a statistical catch-at-age model (SCAA), a Bayesian state-space production model (BSPM) and a Bayesian biomass dynamic model (BBDM). The results from the SS3 model were used to determine the current status of albacore and provide management advice (IOTC 2017), although the results from all the models were generally consistent. Considerable uncertainty exists in the SS3 model results because of uncertainty in CPUE data and length composition data, and a lack of biological information on albacore stocks in the Indian Ocean (IOTC 2017).

The result of the SS3 model indicated that the current (2014) biomass was above the limit reference point (SB2014/SB1950 = 0.37; 80 per cent CI 0.28–0.46) and above the level that supports MSY (SB2014/SBMSY = 1.80; 80 per cent CI 1.38–2.23). Fishing mortality was estimated to be below the level that supports MSY (F2014/FMSY = 0.85; 80 per cent CI 0.57–1.12) (IOTC 2017).

Stock status determination

The assessment indicates that the spawning biomass is above the default limit reference point (0.2B0), and so the stock is classified as not overfished. Fishing mortality across the entire IOTC area is below FMSY, and so the stock is classified as not subject to overfishing.

Bigeye tuna (Thunnus obesus)

Bigeye tuna (Thunnus obesus) 

Line drawing: FAO

Stock structure

The stock structure of bigeye tuna in the Indian Ocean is uncertain, but the species is considered to be a single distinct biological stock for assessments. The assumption of a single stock is based on a genetic study (Chiang et al. 2008) that indicated no genetic differentiation within the Indian Ocean, and tagging studies that have demonstrated large-scale movements of bigeye tuna within the Indian Ocean (IOTC 2014).

Catch history

Annual catches of bigeye tuna in the WTBF varied widely between 1983 and 2004, with the highest catch of more than 900 t in 1987 and the lowest catch of less than 22 t in 1991 (Figure 24.10). Catches have been more stable since 2004, and have not exceeded 200 t. Total international catches in the IOTC area of competence have declined from a peak of more than 160,000 t in 1999 to less than 100,000 t in recent years (Figure 24.11). Bigeye catch was 87,297 t in 2016, which is below the 2016 MSY estimate of 104,000 t, as is the five-year average catch.

Figure 24.10 Bigeye tuna catch and TACC in the WTBF, 1983–2017
Note: TACC Total allowable commercial catch; initial TACC for 19 months.
Source: Australian Fisheries Management Authority
Figure 24.11 Bigeye tuna catch in the IOTC area, 1970–2016
Note: IOTC Indian Ocean Tuna Commission.
Source: IOTC
Stock assessment

Six assessment models were used to assess the Indian Ocean bigeye stock in 2016: SS3, ASPIC, SCAA, an Age Structured Assessment Program (ASAP), a BBDM and a BSPM (IOTC 2017). The SS3 assessment captured uncertainty in the stock–recruitment relationship, as well as the influence of tagging data on the model outcomes, and was used to provide management advice. Current (2015) spawning stock biomass was estimated to be above the level that would produce MSY (SB2015/SBMSY = 1.29; 80 per cent CI 1.07–1.51). Similarly, the assessment indicated that spawning biomass was above 20 per cent of the initial unfished level (SB2015/SB0 = 0.38; 80 per cent CI not available). Fishing mortality was below the level associated with MSY (F2015/FMSY = 0.76; 80 per cent CI 0.49–1.03).

Stock status determination

The SS3 assessment indicates that bigeye tuna spawning stock biomass is above the default limit reference point (0.2B0). As a result, the Indian Ocean bigeye tuna stock is classified as not overfished.Since the current spawning biomass is above the level that would produce MSY, and fishing mortality is below FMSY, the stock is classified as not subject to overfishing.

Yellowfin tuna (Thunnus albacares)

Yellowfin tuna (Thunnus albacares) 

Line drawing: FAO

Stock structure

The stock structure of yellowfin tuna in the Indian Ocean is uncertain, but the species is considered to be a single biological stock for assessments. There have been no ocean-wide genetic studies of yellowfin tuna in the Indian Ocean, but tagging studies have demonstrated large-scale movements of yellowfin tuna in the Indian Ocean, which is consistent with the assumption of a single stock (Langley, Herrera & Million 2012).

Catch history

Historical catches of yellowfin tuna in the WTBF have varied widely from peaks of around 800 t in 1984 and 1995 to less than 15 t in 1991 and 1992 (Figure 24.12). Since the early 2000s, declining effort in the WTBF has resulted in reduced catches of yellowfin tuna. Catches have not exceeded 100 t since 2004 (Figure 24.12). Total international catches in the IOTC area of competence peaked at more than 500,000 t in 2004, then declined for several years (2007–2011) because of the impacts of piracy in the north-west Indian Ocean. From 2012 to 2015, catches remained relatively stable at around 400,000 t. Catches increased to 421,910 t in 2016 (Figure 24.13), which is close to the 2016 MSY estimate of 422,000 t.

Figure 24.12 Yellowfin tuna catch and TACC in the WTBF, 1983–2017
Note: TACC Total allowable commercial catch; initial TACC for 19 months.
Source: Australian Fisheries Management Authority
Figure 24.13 Yellowfin tuna catch in the IOTC area, 1970–2016
Note: IOTC Indian Ocean Tuna Commission.
Source: IOTC
Stock assessment

In 2016, the 2015 yellowfin tuna assessment was updated using a revised composite CPUE series and revised catch estimates. Two assessment models were used (BBDM and SS3; IOTC 2017), although management advice for the stock was based on the results of the SS3 analysis. The results indicate that 2015 levels of fishing mortality were above the level that would achieve MSY (F2015/FMSY = 1.11; 80 per cent CI 0.86–1.36). Current spawning biomass was estimated to be below the level associated with MSY (SB2015/SBMSY = 0.89; 80 per cent CI 0.79–0.99) but above the default limit reference point (SB2015/SB0 = 0.29; 80 per cent CI not available).

Stock status determination

The assessments indicate that fishing mortality is above the level associated with MSY. As a result, the yellowfin tuna stock is classified as subject to overfishing. The biomass is above the default limit reference point (0.2B0), and, as a result, the stock is classified as not overfished.

24.3 Economic status

Key economic trends

Economic surveys have not been conducted in the WTBF since 2001–02 because of the low level of fishing activity. During 2016 and 2017, 95 fishing permits were issued in the fishery. A small number of vessels were operational in the fishery in those years (Table 24.2): three vessels in the 2016 fishing season and four vessels in the 2017 season. Total effort in the fishery increased from 352,274 hooks in 2016 to 417,997 hooks in 2017, but the average number of hooks per active vessel declined. Despite an 18 per cent increase in the total effort in the fishery, catch remained largely unchanged in 2017 at 322 t.

As in previous years, landed catch in the fishery was a small proportion of the TACC during 2017. This high level of latent quota (the extent to which the TACC is not fully caught) and a relatively low participation rate indicate that permit holders expect low profitability from operating in the fishery.

Management arrangements

Before 2010, the WTBF was managed solely under an input control regime in which entry was limited, and gear and operating areas were restricted. In 2010, output controls were introduced in the form of species-specific TACCs, allocated as ITQs. The impact of the move to ITQs has not been measured because of the low participation in the WTBF in recent years. In general, ITQs allow fishers to use input combinations that are more efficient, particularly after any unnecessary input controls are relaxed. The transferability of fishing rights between fishers can also allow more efficient allocation of fishing rights so that catch is taken by the most efficient operators in the fishery. However, the very low levels of catch relative to the TACC in the WTBF are unlikely to provide any incentive for such trade to occur, minimising any efficiency gains.

Performance against economic objective

Although a harvest strategy has not been implemented because of low levels of effort in the fishery, the current management arrangements are unlikely to be constraining fishers’ ability to operate profitably. The high levels of latency experienced in the fishery are more likely to arise from market factors that affect business input costs and international tuna prices. Furthermore, since the WTBF accesses a relatively small component of broader, internationally managed ocean-wide stocks, domestic management actions to control catch are likely to have limited impact on the biomass of these stocks and, therefore, on fishers’ ability to access the resource for profitable operations. Hence, the economic objective of maximising net economic returns is likely being met for the fishery, as constraints to further fishing appear to be market related rather than arising from management arrangements.

24.4 Environmental status

The WTBF has been granted continued export approval under the Environment Protection and Biodiversity Conservation Act 1999, expiring on 28 November 2019. Conditions of export approval include a requirement to develop and implement a harvest strategy in the WTBF. Because of the very low effort in the fishery, the harvest strategy has not been implemented. A revised harvest strategy that takes different levels of effort into account is currently being developed.

AFMA’s ecological risk assessment examined 187 fish species in the WTBF (38 chondrichthyans and 149 teleosts), all of which were classified as being at low risk of potential overfishing, based on the level 3 Sustainability Assessment for Fishing Effects analysis (Zhou, Smith & Fuller 2009). Although no shark species were identified as high risk, an increase in effort could move some species to a higher-risk category. A priority action identified in the WTBF ecological risk management report is to monitor the catch of, and level of interaction with, sharks. Management of shark interactions in this fishery will be reviewed if the landed amount of any one shark species exceeds 50 t within a year (AFMA 2010). Trip limits on sharks apply, depending on species.

AFMA publishes quarterly logbook reports of interactions with protected species on its website. In 2017, 409 shortfin mako sharks (Isurus oxyrinchus)were hooked in the WTBF; 1 was dead, and 408 were released in an unknown condition. Nine porbeagles (Lamna nasus) were also released in unknown condition. Two New Zealand fur seals (Arctocephalus forsteri) were hooked and released alive. Thirteen leatherback turtles (Dermochelys coriacea)were also hooked and released alive, as were five loggerhead turtles (Caretta caretta). One wandering albatross (Diomedea exulans), one shy albatross (Thalassarche cauta) and two unidentified albatrosses were all dead after being hooked. Finally, nine flesh-footed shearwaters (Puffinus carneipes) were hooked; eight were released alive, and one was dead.

24.5 References

AFMA 2010, Ecological risk management: report for the Western Tuna and Billfish Fishery, Australian Fisheries Management Authority, Canberra.

Chiang, H-C, Hsu, C-C, Wu, GC-C, Chang, S-K & Yang, H-Y 2008, ‘Population structure of bigeye tuna (Thunnus obesus) in the Indian Ocean inferred from mitochondrial DNA’, Fisheries Research, vol. 90, pp. 305–12.

DAFF 2007, Commonwealth Fisheries Harvest Strategy: policy and guidelines,Australian Government Department of Agriculture, Fisheries and Forestry, Canberra.

Davies, C, Campbell, R, Prince, J, Dowling, N, Kolody, D, Basson, M, McLoughlin, K, Ward, P, Freeman, I & Bodsworth, A 2008, Development and preliminary testing of the harvest strategy framework for the Western Tuna and Billfish Fishery, CSIRO, Hobart.

IOTC 2014, Report of the seventeenth session of the Scientific Committee, Victoria, Seychelles, 8–12 December 2014, IOTC-2014-SC-R[E], Indian Ocean Tuna Commission, Victoria, Seychelles.

—— 2017, Report of the twentieth session of the Scientific Committee, Seychelles, 30 November – 4 December 2016, IOTC-2017-SC-R[E], IOTC, Victoria, Seychelles.

Langley, A, Herrera, M & Million, J 2012, ‘Stock assessment of yellowfin tuna in the Indian Ocean using MULTIFAN-CL’, paper presented at the 14th session of the IOTC Working Party on Tropical Tunas, Mauritius, 24–29 October 2012, IOTC-2012-WTT14-38_Rev 1, IOTC, Victoria, Seychelles.

Mamoozadeh, NR, McDowell, JR & Graves, JE 2017, ‘Preliminary results from an assessment of genetic population structure for striped marlin (Tetrapturus audax) in the Pacific and Indian oceans’, paper presented at the 15th session of the IOTC Working Party on Billfish, San Sebastián, Spain, 10–14 September 2017, IOTC-2017-WPB15-28, IOTC, Victoria, Seychelles.

Montes, I, Iriondo, M, Manzano, C, Arrizabalaga, H, Jiménez, E, Angel Pardo, M, Goni, N, Davies, CA & Estonba, A 2012, ‘Worldwide genetic structure of albacore Thunnus alalunga revealed by microsatellite DNA markers’, Marine Ecology Progress Series, vol. 471, pp. 183–91.

Muths, D, LeCouls, S, Evano, H, Grewe, P & Bourjea, J 2013, ‘Multi-genetic marker approach and spatio-temporal analysis suggest there is a single panmictic population of swordfish Xiphias gladius in the Indian Ocean’, PLoS One, vol. 8, e63558.

Zhou, S, Smith, T & Fuller, M 2009, Rapid quantitative risk assessment for fish species in major Commonwealth fisheries, report to AFMA, Canberra.

Last reviewed:
22 Oct 2018