Eastern Tuna and Billfish Fishery

Annual Status Report 2005-2008

6. Status of target stock

Resource concerns
Stock assessments and recovery strategies

6.1. Resource concerns

The five target species in the ETBF are highly migratory and internationally managed by WCPFC, therefore it is important to note that any assessment of resources is based on the WCPFC assessment (See Section 6.2: Stock assessments and recovery strategies).

Table 5: BRS Fishery Status Report 2006 results for target species in the ETBF (Source: BRS,2007[5])

Yellowfin tuna	Overfishing in the western and central Pacific Ocean, but stocks not overfished
Bigeye tuna	Overfishing in the western and central Pacific Ocean, but stocks not overfished
Albacore tuna	Not overfished and not subject to overfishing in the South Pacific
Broadbill swordfish	Overfished status uncertain and overfishing status uncertain in the south-western Pacific
Striped Marlin	Overfished status uncertain and overfishing status of striped marlin uncertain in the south-western Pacific

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6.2.Stock assessments and recovery strategies

Albacore

The current stock assessment for albacore tuna in the south-Pacific (2005) identified albacore fishing mortality well below the mortality associated with Maximum Sustainable Yield (MSY) and total biomass well above the level capable of supporting MSY. As a preliminary measure the WCPFC has implemented boat limits to prevent mobilisation of new fleets that would expand albacore catch levels but currently no need for a stock recovery strategy exists. A brief update of the stock assessment in 2006 reinforced the conclusion that there was no concern regarding the biological sustainability of the stock at the current level.

Striped Marlin

The first formal stock assessment for striped marlin in the south-west Pacific was conducted in 2006 and results were surrounded by considerable uncertainty. Some model runs indicated that biomass and fishing effort were close to exceeding MSY. The WCPFC has implemented boat country limits in the south Pacific south of 15° south to prevent further increases in fishing mortality, which was the recommendation from its Scientific Committee.

Broadbill Swordfish

The first formal stock assessment for broadbill swordfish in the south-west Pacific was conducted in 2006 and results were surrounded by considerable uncertainty. Some model runs indicated that biomass and fishing effort were close to exceeding MSY. Australia and New Zealand completed the stock assessment at a time that catch rate declines were occurring in the ETBF, indicating localised depletion of stock. No regional stock recovery strategy has been developed for swordfish due to disagreement between the parties but boat country limits have been implemented in the south-west Pacific south of 20° south. However, AFMA has implemented domestic arrangements (an annual total allowable catch (TAC) of 1,400 tonnes on swordfish since 2006), which is expected to stabilise catch rates and prevent further depletion of stock in the local area.

Yellowfin Tuna

The 2006 stock assessment of yellowfin tuna identified overfishing likely to be occurring in the Western and Central Pacific Ocean (WCPO) but the stock was not overfished. The WCPFC Scientific Committee recommended a 10% reduction in fishing mortality to maintain stock at levels capable of supporting MSY. The 2007 stock assessment however was more positive indicating that current exploitation rates were at the limit of MSY. No stock recovery strategy has been developed yet for yellowfin tuna by WCPFC.

Bigeye Tuna

The current stock assessment for bigeye tuna (2006) identified overfishing highly likely to be occurring in the WCPO but the stock was not yet overfished. The fishing mortality was above FMSY but biomass was above BMSY. The WCPFC has failed over three consecutive sessions to implement arrangements that would reduce fishing mortality. Australia assisted in tabling a Forum Fisheries Agency (FFA) draft measure for bigeye and yellowfin tuna to address overfishing of stock which combined catch retention, FAD closure and longline reduction. However the measure was not adopted by the WCPFC due to disagreement between member states.

The stock assessments for yellowfin and bigeye tuna indicated that most of the overfishing is occurring in equatorial waters whilst only moderate fishing mortality is occurring in more temperate waters (such as off Australia). Of particular concern is the capture of juvenile yellowfin and bigeye tuna when fishing on Fishery Aggregation Devices (FADs). AFMA does not allow the use of FADs in Australia. Due to the low catches in temperate waters, any stock recovery strategy to be effective, will need to address as a priority, fishing in equatorial waters where the highest levels of fishing pressure and exploitation of stock are occurring.

Stock assessments of south pacific albacore, swordfish and bigeye tuna will be revised in 2008.

Table 6: Summary of stock assessments completed by the WCPFC for relevant ETBF target species

WCPFC Scientific Committee Stock Assessments
Species	Year of stock assessment	Summary of main results
Yellowfin tuna	2005	Overfishing of yellowfin is now likely to be occurring in the WCPO. While the stock is not yet in an overfished state further biomass decline is likely to occur at 2001−2003 levels of fishing mortality.
	2006	Yellowfin stock in the WCPO is not in an overfished state. However, biomass levels in recent years have been declining and the probability of the stock becoming overfished is increasing over time. Overfishing of yellowfin is likely to be occurring in the WCPO. While the stock is not yet in an overfished state further biomass decline is likely to occur at 2001−2004 levels of fishing mortality.
	2007	Yellowfin stock in the WCPO is not in an overfished state. It is not possible to make a definitive statement as to whether or not overfishing of yellowfin is occurring in the WCPO. Nonetheless, current exploitation rates are likely to be, at least, approaching the MSYF level and any further increase in exploitation rates will not result in an increase in equilibrium yields from the stock under the current age specific pattern of exploitation. On that basis, the WCPO yellowfin tuna fishery can be considered to be fully exploited.
Bigeye tuna	2005	A high probability that current fishing mortality on bigeye tuna is above MSY levels, but that current total biomass remains above the MSY level. Adult biomass could be above or below the MSY level depending on the analysis chosen.
Bigeye tuna	2006	Bigeye stock in the WCPO is not in an overfished state due to average recruitment. However, biomass levels in recent years have been declining and the probability of the stock becoming overfished is increasing over time. Overfishing of bigeye is occurring in the WCPO with high probability. While the stock is not yet in an overfished state further biomass decline is likely.
Albacore tuna	2005 (with an update in 2006)	The current levels of exploitation of the total biomass are low. Nevertheless, the current level of longline catch is estimated to be having a measurable impact on the portion of the stock vulnerable to the longline fishery.
Broadbill swordfish	2006	The data are not sufficient to estimate a stock recruitment relationship reliably,and most or all models explored suggest some form of non-stationary (or at least highly variable) recruitment dynamics.
Striped marlin	2006	Current stock status is uncertain. There appears to be no potential to substantially increase the current level of yield from the stock. However, the fishery has supported catches at about the MSY level for the last 20 years at a relatively constant level of fishing effort. Consequently, there is no indication that current exploitation rates are having a deleterious impact on the productivity of the stock. Regardless, several of the plausible model scenarios investigated indicate that current levels of fishing mortality may approximate or exceed the reference level and current biomass levels. On this basis, it is recommended that there be no increase in fishing mortality (fishing effort).

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(5) BRS (2007) “Regional Profile – East Marine Region: Description of commercial, recreational and charter fishing activities”. Bureau of Rural Sciences. 171pp.

Page last updated 23 April, 2008