Marlin, blue

Makaira nigricans

Method of production — Caught at sea
Capture method — Longline
Capture area — Atlantic (FAO 21,27,31,34,41,47)
Stock area — Atlantic
Stock detail

All Areas


Picture of Marlin, blue

Sustainability rating five info

Sustainability overview

The stock has been overfished for the last 10-15 years, and the last assessment undertaken in 2011, using data up to 2009, indicated that the fishery was in an overfished state (Spawning Stock Biomass, SSB, at 0.67 SSB MSY) and was subject to overfishing (Fishing mortality, F, at 1.63 F MSY). The fishery is in need of an updated stock assessment. At the time of the last assessment, it was noted that unless the catches of 3,358 t (2010) were substantially reduced, the stock will continue to decline. Reported catches have reduced in recent years (provisional 2016 catch is 1,295 t and the 2011-2015 average is 1,843 t) yet there are concerns over significant unreported catches, particularly in artisanal fisheries. As part of a rebuilding plan to recover the stock to sustainable levels (BMSY), there is a total allowable catch in place (2016-2018) with country specific limits, and there is a minimum landing size for recreational catches. Better reporting of landed and non-landed catches is needed to evaluate the effectiveness of the plan. Four countries (Brazil, Canada, Mexico, and the United States) mandate or encourage the use of circle hooks on their pelagic longline fleets as an effective measure at reducing marlin mortality, whilst not reducing target species landings. Pelagic longlining can be associated with significant bycatch of other billfish and vulnerable species such as sharks, turtles and seabirds. Whilst some mitigation measures are in place, their effectiveness has not been evaluated and better data collection & reporting is needed. Observer coverage is 5% on large longliners, yet this is not being complied with by several countries and 20% coverage is recommended.

Biology

Blue marlin are highly migratory and are found throughout tropical and temperate waters worldwide. Migrations include trans-Atlantic as well as trans-equatorial movements. They are usually solitary, large predators with an average weight of 100-175 kg. Sexually mature at 2-4 years, they spawn in tropical and sub-tropical waters in the summer and autumn, and are found in colder temperate waters during the winter. Young marlin are one of, if not the, fastest growing of all bony fish.

Stock information

Criterion score: 1 info

Stock Area

Atlantic

Stock information

Atlantic blue marlin stocks are managed by ICCAT - the International Commission for the Conservation of Atlantic Tuna. The stock has been overfished for the last 10-15 years, and the last assessment undertaken in 2011, using data up to 2009, indicated that the fishery was in an overfished state (Spawning Stock Biomass, SSB, at 0.67 SSB MSY) and is subject to overfishing (Fishing effort, F, at 1.63 F MSY). The fishery is in need of an updated stock assessment. At the time of the last assessment, it was noted that unless the catches of 3,358 t (2010) were substantially reduced, the stock will continue to decline. Reported catches have reduced in recent years (provisional 2016 catch is 1,295 t and the 2011-2015 average is 1,843 t) yet there are concerns over significant unreported catches, particularly in artisanal fisheries. Over the last 20 years, Antillean artisanal fleets have increased the use of Moored Fish Aggregating Devices (MFADs) to capture pelagic fish. Catches of blue marlin caught around MFADs are known to be significant and increasing in some areas, however reports to ICCAT on these catches are incomplete. Recent reports from purse seine fleets in West Africa suggest that blue marlin is more commonly caught with tuna schools associated with FADs than with free tuna schools. Furthermore, the Scientific Committee is concerned with the significant increase in the contribution from non-industrial fisheries to the total blue marlin harvest and that these fisheries are not fully accounted for in the current ICCAT database.

Blue marlin are listed globally as Vulnerable by the International Union for the Conservation of Nature (IUCN), and Endangered in the Gulf of Mexico.

Management

Criterion score: 0.5 info

Similar to most tuna stocks, blue marlin range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. To try and address this, Intergovernmental Regional Fisheries Management Organisations (RFMOs) have been established. There are five main tuna RFMOs worldwide and it is their responsibility to carry out data collection, scientific monitoring and management of these fisheries. This stock is managed and assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Whilst the RFMOs are responsible for the development of management and conservation measures, the degree to which they are implemented, monitored and enforced still varies significantly between coastal states. There remain large data deficiencies in most tuna and billfish fisheries, particularly with regards to fine scale spatial and temporal data for both target and especially for vulnerable bycatch species. For this reason, it is important to choose blue marlin that has been caught by vessels that are well regulated by their flag state.

The total catch limit for blue marlin for 2016-2018 is 2,000 t, with individual catch limits assigned to each country. Countries approaching their catch limits should try to release any live blue marlin that have been caught, in a way that maximises their chances of survival. While there have been studies and data collected on the live release of blue marlin, there is not enough information on the proportion of fish being released alive for all fleets to evaluate the effectiveness of this. For recreational fisheries, fish must be greater than 251cm and any blue marlin caught may not be sold on. The current management plan has the potential of recovering the blue marlin stock to the BMSY level if properly conducted. However, the scientific committee is concerned with significant increases in catch by non-industrial fisheries, which are not fully accounted for. This data limitation is of serious concern for future assessments, prevents assessment of the effectiveness of current regulations, and reduces the likelihood that any additional management measures will work. Currently, four countries (Brazil, Canada, Mexico, and the United States) mandate or encourage the use of circle hooks on their pelagic longline fleets as an effective measure at reducing marlin mortality, whilst not reducing target species landings. Recent reports from purse seine fleets in West Africa suggest that blue marlin is more commonly caught with tuna schools associated with FADs than with free tuna schools.

Other management measures of note include:
There is a mandatory level of observer coverage of 5%, which may not have been implemented by many fleets, although some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips. This is in spite of scientific committee recommendation of a minimum of 20% for accurate reporting of bycatch. Purse seine and longline vessels over 20m long are encouraged to increase their observer coverage from the required minimum. Vessel Monitoring Systems are required for all vessels over 24m.
In 2015 a working group was formed to look at ways to reduce juvenile catches of bigeye and yellowfin tuna caught in FAD fishing.
Drift nets are banned in the Mediterranean.
ICCAT maintains lists of vessels authorised to fish for tuna and tuna-like species in the ICCAT area, and those caught carrying out Illegal, Unreported or Unregulated activities.
At-sea transhipment is prohibited unless pre-authorised and the vessel has an observer on board.
In 2017 ICCAT banned the discarding of skipjack, yellowfin and bigeye.
In 2016 the Commission passed measures to strengthen and streamline its compliance assessment process and to develop a scheme of responses to non-compliance.

Capture Information

Criterion score: 0.75 info

Blue marlin in the Atlantic are mainly landed as by-catch in longline fisheries for tuna and swordfish, and to a lesser extent as bycatch in purse seine fisheries and in directed recreational and artisanal fisheries. Recent reports from purse seine fleets in West Africa suggest that blue marlin is more commonly caught with tuna schools associated with FADs than with free tuna schools. Over the last 20 years, Antillean artisanal fleets have increased the use of Moored Fish Aggregating Devices (MFADs) to capture pelagic fish. Catches of blue marlin caught around MFADs are known to be significant and increasing in some areas, however reports to ICCAT on these catches are incomplete. Pelagic longlines in the Atlantic need to reduce their interactions with vulnerable species including large sharks, turtles, birds and some billfish species like blue marlin. It is positive to see Brazil, Canada, Mexico and the U.S. mandating or encouraging the use of circle hooks to reduce mortality of blue marlin. Such measures should be considered for adoption more widely.

ICCAT aims to take an ecosystem-based and precautionary approach to fisheries management. In order to protect juvenile swordfish, a closure period applies to longline vessels targeting Mediterranean albacore from 1 October to 30 November each year.

For sharks: Countries are required to develop and submit National Plans of Action for the conservation and management of sharks. Sharks must be fully utilised (e.g. no removal of fins). Sharks must be released wherever possible (if not being directly targeted) and countries must try to minimise bycatch of sharks (although no gear-specific measures are identified). Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako can be caught and retained, but as of 2017 the country’s law must require a minimum length of 180cm for males and 210cm for females, otherwise, shortfin makos caught alive must be released unharmed. This is expected to prevent the stock’s currently poor state from worsening, and a rebuilding plan will be developed for 2019. In 2016 additional measures for blue shark were introduced, mainly focussed on improved data recording, with potential to introduce Harvest Control Rules. A catch limit of 39,102 t was also introduced in the north Atlantic (but none for the south Atlantic): if exceeded the commission has committed to reviewing the effectiveness of its blue shark management measures. Preliminary catch in 2016 was 42,117 t. Porbeagle is overfished throughout the Atlantic, significantly so in the northwest, and for the north Atlantic overall it is predicted to take at least 30 years to recover if there was zero fishing mortality. The main porbeagle-directed fisheries (EU, Uruguay and Canada) have closed, and ICCAT have a recommendation to release live porbeagle unharmed, but it is still caught incidentally and discarded, and also landed by other fleets. Currently there is not enough data to properly assess the status of many pelagic sharks (no assessments have been carried out for the Mediterranean).

For seabirds: There are particular concerns over the status of albatross and petrels. South of 20 degrees South, vessels must use bird-scaring lines. Swordfish vessels are exempt from this if they fish at night and weight their hooks. South of 25 degrees South, vessels must use 2 of the three measures mentioned. In the Mediterranean, these measures are voluntary. However, recommended best practice is to use all three of the aforementioned measures for all longline vessels.

For turtles: Longliners must carry equipment and have training to enable them to safely release turtles that have been caught. Countries are required to research and trial circle hooks for longliners. The scientific committee recommends that longliners targeting swordfish and sharks must use either large circle hooks or finfish bait as mitigation, but this has not been implemented.

There is a mandatory level of observer coverage of 5%, which may not have been implemented by many fleets, in spite of scientific committee recommendation of a minimum of 20% for accurate reporting of bycatch. However, some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips.

References

Collette, B., Acero, A., Amorim, A.F., Boustany, A., Canales Ramirez, C., Cardenas, G., Carpenter, K.E., de Oliveira Leite Jr., N., Di Natale, A., Die, D., Fox, W., Fredou, F.L., Graves, J., Guzman-Mora, A., Viera Hazin, F.H., Hinton, M., Juan Jorda, M., Minte Vera, C., Miyabe, N., Montano Cruz, R., Nelson, R., Oxenford, H., Restrepo, V., Salas, E., Schaefer, K., Schratwieser, J., Serra, R., Sun, C., Teixeira Lessa, R.P., Pires Ferreira Travassos, P.E., Uozumi, Y. & Yanez, E., 2011. Makaira nigricans. The IUCN Red List of Threatened Species 2011: e.T170314A6743776. Available at http://dx.doi.org/10.2305/IUCN.UK.2011-2.RLTS.T170314A6743776.en [Accessed on 05.12.2017].

ICCAT, 2017. Report of the Standing Committee on Research and Statistics (SCRS) of the International Commission for the Conservation of Atlantic Tunas, 2-6 October 2017, Madrid, Spain. 465 pp. Available at http://www.iccat.int/com2017 [Accessed on 27.11.2017].

ICCAT, 2017. Resolutions, Recommendations and other Decisions. Available at http://www.iccat.es/en/RecsRegs.asp [Accessed on 12.12.2017]

MSC, 2017. Marine Stewardship Council: Track a Fishery. Available at https://fisheries.msc.org [Accessed on 20.11.2017].