Bigeye tuna

The Oceanic Fisheries Programme (OFP) of the Secretariat of the Pacific (SFP), conducted the most recent assessment for bigeye tuna in the Western and Central Pacific Ocean (WCPO) in 2017 (McKechnie et al. 2017).

Stock assessments of bigeye tuna in the WCPO have been conducted regularly since 1999. The most recent assessment was conducted in 2017 and included catch, effort, length-frequency and weight-frequency data from 1952-2015. This updated model included the following changes from the 2014 assessment: 

- Standardied catch per unit effort (CPUE) indices calculated from the recently collated operational longline CPUE dataset

- Investigating alternative spatial structure

- Investigate use of a new growth model

- Implementation of new features developed in the Multi-Fan CL model

In 2018 the SPC, using updated age and growth information, re-evaluated the status of bigeye tuna. The analysis used the same methods as used during the 2017 assessment (Vincent et al. 2018).

The most recent scientific advice, based on the 2016 assessment, is that the Western and Central Pacific Fisheries Commission (WCPFC)  should continue to consider measure to reduce fishing mortality of juvenile bigeye tuna. Fishing mortality levels should not be increased from current levels in an effort to allow the population to be at the least maintained or potentially increase {WCPFC 2017}.

There is currently a limit but no target reference point adopted by the Western and Central Pacific Fisheries Commission for bigeye tuna (Vincetn et al. 2018).

The stock is currently not overfished and overfishing is not occurring (McKechnie et al., 2017)(Vincent et al. 2018).

Last updated on 16 Jan 2018

The spawning potential of bigeye tuna in the western and central Pacific Ocean (WCPO) began to decline after a stable period during the 1950’s. The most rapid declines occurred through the mid-1970’s and since then, the decline has been more gradual. Fishing mortality rates for adults increased throughout the time period and for juveniles increased through the late 1990’s, being stable since {McKenchie et al. 2017}. Short term projections conducted in  indicate the current spawning biomass is likely to remain above the limit reference point (Scott et al. 2017).

There are management measures in place for bigeye tuna in the western and central Pacific Ocean (WCPO) longline and troll and pole fisheries. The measures that are in place include catch limits for bigeye tuna caught in longline fisheries and in fisheries other than longline, the total fishing effort must be below the average level from 2001-2004 or for 2004 (WCPFC 2017).The most recent management measures for this species were adopted in 2017 (WCPFC 2017). These measures apply to the longline, purse seine and other surface fisheries.  The WCPFC has implemented several management measures specific to the purse seine fisheries. For purse seine fisheries, there is a three month prohibition (July, August and September) on setting on fish aggregating devices (FAD’s) for all purse seine vessels in EEZ’s and the high seas in the area between 200 N and 200 S. In addition, member nations (except Kiribati and Philippines) must iprohibit FAD fishing (deployement and service as well) during an additional two sequential months, either April-May or November-December (WCPFC 2017). Coastal CCM's must also adhere to purse seine effort limits in their EEZs (WCPFC 2017). Other CCMs (non Small Islands Developing States and Indonesia) must limit the number of purse seine vessels larger than 24 m operaring between 200 N and 200 S to the level required under CCM 2013-01 (WCPFC 2017). Member nations must have a FAD management plan in place to help reduce the capture of small bigeye and yellowfin tuans, and implementing FAD closures and discarding bigeye, skipjack or yellowfin tuna is prohibited {WCPFC 2012a}{WCPFC 2013b}{WCPFC 2016b}. In addition, member countries of the Parties to the Nauru Agreement have agreed to use a regional fishing vessel register, abide by a high seas pocket area closures, are prohibited from fishing on FAD’s, utilize a Vessel Day Scheme and retain all catch {PNA 2013}{PNA 2012} [PNA 2010}{WCPFC 2016b}{WCPFC 2016c}.

In addition, biomass based limit reference points have been adopted by the Western and Central Pacific Fisheries Commission (WCPFC) for bigeye tuna and are used to determine the status of tuna populations. Target reference points are not yet in place and there are no harvest control rules (WCPFC 2017). However, the WCPFC has a working group that is currently working on identifying potential target reference points and a harvest control rule {WCPFC 2016d}.

Bigeye tuna are included in a Conservation and Management Measure (CMM) for tropical tunas in the WCPO (WCPFC 2017).  

The Western and Central Pacific Fisheries Commission (WCPFC) has a compliance monitoring scheme in place that assess’s members compliance with obligations, identifies areas of conservation and management that may need refinement, responds to non-compliance and monitors and resolves non-compliance issues. The Commission evaluates compliance by members annually with respect to: catch and effort limits and reporting for target species, spatial and temporal closures, observer and Vessel Monitoring Systems (VMS) coverage and provision of scientific data {WCPFC 2012b}.

Vessel Monitoring Systems are required on all vessels fishing for highly migratory species in the Western and Central Pacific Ocean south of 20N and east of 175E. The area north of 20N and west of 175W will have an activation date for VMS’s set at a later time {WCPFC 2012b}. There are measures in place allowing for the boarding and inspection of vessels in the Convention Area {WCPFC 2006} and the WCPFC maintains a list of illegal, unreported and unregulated vessels {WCPFC 2010}. However, assessing the effectiveness of these enforcement measures is difficult because there is a general lack in the transparency of information with regards to surveillance activities, infractions and enforcement actions and outcomes {Gilman et al. 2013}.

The Western and Central Pacific Ocean (WCPO) tuna longline fisheries incidentally capture green, hawksbill and leatherback sea turtles, which are currently listed on CITES Appendix I, meaning they are threatened with extinction and international trade is banned. The International Union for Conservation of Nature (IUCN) has listed green turtles as Endangered and hawksbill and leatherback turtles as Critically Endangered. Leatherback turtles have also been listed as Endangered on the Endangered Species Act since 1970 and Olive Ridley turtles as Threatened since 1978. The IUCN classified loggerhead turtles as Endangered in 1996, although it has been suggested that this needs to be updated {Marine Turtle Specialist Group 2006). In the North Pacific Ocean, loggerheads have been listed as Endangered on the Endangered Species Act list since 1978 {NMFS 2012}. Purse seine (associated) fisheries also capture green, hawksbill, and olive Ridely sea turtles.

Marine mammals interactions are not common in longline fisheries operating in the WCPO {Molony 2005} but false killer whales, rough-toothed and short-beaked dolphins are reported as bycatch in purse seine fisheries {OFP 2012}.

Sea birds are most commonly encountered in the southern part of the WCPO. Common species include Black-browed albatross, grey petrel, flesh-footed shearwater, light manteled albatross, Salvin’s albatross, wandering albatross and white-chinned petrel {Birdlife International}.

The Western and Central Pacific Fisheries Commission (WCPFC) has adopted several management measures to protect vulnerable bycatch species. For example, WCPFC members are asked to implement the International Plan of Action for Reducing Incidental Catches of Seabirds in Longline Fisheries. Vessels fishing north of 23N in the WCPO are required to use at least two mitigation measures including at least one of the following: side setting, night setting, tori line or weighted branch line. Members must submit annual reports detailing the mitigation measures used and are encouraged to undertake additional mitigation research {WCPFC 2012d}. Members of the WCPFC are also to implement the FAO Guidelines to Reduce Sea Turtle Mortality in Fishing Operations. Proper handling and release guidelines should be used when hard-shell turtles are incidentally captured and longline vessels must carry line cutters and de-hookers to allow for the safe handling and release of turtles. Longline fisheries are also urged to research mitigation techniques such as the use of circle hooks {WCPFC 2008}. In addition, fisheries observers record and report interactions with seabirds and turtles {WCPFC 2012d}{WCPFC 2008}.

The Western and Central Pacific Ocean (WCPO) longline fisheries catch a number of other species of fish, including billfish, other tuna species, and sharks. The troll fishery catches small amounts of other tuna species and fish.

Common bycatch species in the longline fisheries include blue, shortfin mako, silky and oceanic whitetip sharks, opah, and blue, striped and black marlin. In the purse seine fishery, silky and whale (unassociated) sharks are also incidentally captured. Oceanic whitetip, silky and shortfin mako sharks and striped marlin are either overfished or their status is unknown {Rice and Harley 2012a,b}{Clark 2011}{Lee et al. 2012}.

Members of the Western and Central Pacific Fisheries Commission (WCPFC) are prohibited from retaining, transshipping, storing or landing oceanic whitetip sharks and any incidentally caught sharks should be released, the incident recorded and reported {WCPFC 2012e}. Members are also to implement the FAO International Plan of Action for the Conservation and Management of Sharks and National Plans of Action should have policies in place to reduce waste and discarding of sharks. Information on catch and effort for key species is to be reported and shark finning is banned (5% ratio) {WCPFC 2010}. In addition, a phased reduction in catches of striped marlin in the North Pacific began in 2010, and was scheduled to run through 2012, resulting in an 80% reduction of 2000-2003 levels. Individual countries were to identify ways to accomplish this {WCPFC 2010b}. Member countries were also to limit the number of fishing vessels targeting swordfish to levels from any year between 2000 and 2005 {WCPFC 2009}.

Purse seine vessels in the WCPO are prohibited from setting on a school of tuna with a whale shark, although members that fish north of 30N can implement this measure or a comparable measure. If a whale shark is incidentally encircled, the vessel must take reasonable steps to ensure its safe release and report the incident. However, these measures did not become mandatory until January 1, 2014 {WCPFC 2012f}.

The impact of pelagic longlines, purse seine's and troll/pole fishing gears, which are used to capture bigeye tuna in the western and central Pacific Ocean, on bottom habitats is minimal.

The Western and Central Pacific FIsheries Commission (WCPFC) has a time/area closure on purse seine sets on fish aggregating devices (FADs) and other floating objects by purse seine vessels for three months annually in the area bounded by 20ºN and 20ºS (WCPFC, 2008a, 2009a). In 2008, the Parties to the Nauru Agreement, a regional agreement establishing terms and conditions for foreign access to the Exclusive Economic Zones of eight Pacific Island Countries, closed to purse seine fishing two areas of high seas international waters that are enclosed by the Parties’ domestic waters (PNA, 2008). These areas were modified slightly in 2016 {WCPFC 2016c}. There are no closed ares to longline fishing.