Yellowfin tuna

Stock assessments of yellowfin tuna in the eastern Pacific Ocean are conducted by the Inter-American Tropical Tuna 7Commission (IATTC). An updated assessment was conducted in 2019. The Stock Synthesis model, a statistical age-structured model was used in this and previous assessments. Information needed for this model includes, catch, discards, indices of abundance and size composition data from fisheries that capture yellowfin tuna (Minte-Vera et al. 2019). This was considered an 'updated' assessment so the same base case model as used in the previous assessment was used with updated data (Minte-Vera et al. 2019).

In 2013 the IATTC scientific staff made the following recommendations to the Commission in 2013 for tunas and sharks: 1. The current tuna management plan should be continued through 2014 because there is evidence that fishing mortality for bigeye tuna may still be too high. In addition, yellowfin tuna longline catches should be reported monthly in addition to bigeye catches and countries reporting more than 500 t of yellowfin catch should provide reports to the IATTC. 2. A harvest control rule that requires effort to be reduced once fishing mortality exceeds the maximum sustainable yield should be adopted and 3. Longline vessels that target sharks should not increase their effort and reporting of shark catches should be mandatory for all vessels {IATTC 2013a}.

In 2014, the Scientific Committee made several additional recommendations including conducting a feasibility study for sampling lengths from adult tuna on a regular basis, combining observer data into a central database, analyze movement patterns of bigeye tuna and that ecological risk assessments for silky and hammerhead sharks should be reported (IATTC 2014). In 2016, the Scientific Committee advised that the current conservation and management measures in place for yellowfin and other tropical tuna should continue, with the addition of extra purse seine closure days (87 instead of 62) (IATTC 2016).

In 2018, the IATTC scientific staff recommended putting a limit on the total number of purse seine (both associated and unassociated) sets (IATTC 2018). In 2019, due to issues with the yellowfin tuna stock assessment, the IATTC scientific staff was unable to make any management recommendations specific to yellowfin tuna. They instead provided a similar recommendation to that from 2018 to maintain the current management resolution and limit the total number of purse seine (associated and unassociated) sets in 2020 to 15,723  (IATTC 2019). The IATTC Scientific Advisory Committee did not endorse this recommendation from the IATTC staff and provided no additional management advice for yellowfin tuna in 2019 (final report not published yet, personal communication from the meeting).

Fishing mortality rates for yellowfin tuna are above maximum sustainable yield (MSY) levels (F multiplier = 089). The spawning biomass ratio at the start of 2019 was below MSY levels. Yellowfin tuna in the eastern Pacific Ocean are overfished and undergoing overfishing (Minte-Vera et al. 2019).

Management measures specific to pelagic longline fisheries operating in the Eastern Pacific Ocean include catch limits (combined) for bigeye and yellowfin tuna by set type for large purse seine vessels (IATTC 2017). IATTC currently uses an interim limit reference point for yellowfin tuna but target reference points and harvest control rules are not used. Management measures specific to the purse seine fisheries include a mandatory closure for 72 days during one of two predefined time periods and there is an additional purse seine closure between October 9 and November 8th in the area of 96⁰ and 110⁰W and between 4⁰N and 3⁰S (IATTC 2017). If a fisheries observer is onboard from the On-Board Observer Program of the Agreement on the International Dolphin Conservation Program (AIDCP), the vessels (182-272 metric tons carrying capacity) can make one 30 day trip during the specified closures dates. An additional time/area closure off the coast of Central and South America for purse seine vessels is also in place (IATTC 2017). Discarding bigeye, skipjack and yellowfin tuna is prohibited {IATTC 2013}. Purse seine vessels are also prohibited from setting on data buoys {IATTC 2010}. There are no management measures specific to the longline fishery for yellowfin tuna (IATTC 2017). IATTC has a multi-annual conservation program in place to monitor yellowfin tuna populations. The Conservation Measures were expanded during 2017 for the 2018-2020 fishing seasons (IATTC 2017).

There is currently no TAC in place for yellowfin tuna.

The longline fisheries operating in the eastern Pacific Ocean (EPO) that capture yellowfin tuna can also incidentally catch several species of sea turtles currently listed under CITES Appendix I. Purse seine fisheries have some interactions with sea turtles, but far less than in the longline fisheries. The troll and pole fisheries for yellowfin tuna do not incidentally capture any of these species.

Green, hawksbill, leatherback, loggerhead and olive ridley sea turtles have been reported as incidentally captures in longline fisheries operating in the EPO. The International Union for the Conservation of Nature (IUCN) classifies green, leatherback and loggerhead turtles as Endangered, hawksbill as Critically Endangered, and olive ridley as Vulnerable (www.iucn.org).

Marine mammal interactions are not common in this fishery.

Several species of seabirds, including black-footed, laysan and waved albatross. Black-footed, laysan albatross are considered Near Threatened by the IUCN and waved albatross as Critically Endangered.

The Inter-American Tropical Tuna Commission (IATTC) has put several management measures aimed at bycatch species into place. IATTC member countries are to implement an International Plan of Action for Seabirds. Two seabird mitigation methods are requiredon vessels larger than 20 m fishing in specific areas. A 3 year program to reduce the impact of fishing on sea turtles has been put into place. This plan requires reporting of any interaction and carrying of proper handling and release gears. Shark finning is banned (5% rule) and oceanic whitetip sharks are prohibited from being retained (IATTC 2011b)(IATTC 2011c)(IATTC 2005)(IAC 2012). Purse seine fisheries fishing on fish aggregating devices (FADs) must use specific methods designed to avoid entangling sea turtles or other bycatch species. Any interactions must be reported and sea turtles are to be released (IATTC 2012)(IATTC 2007).

The dolphin set fishery has historically had interactions with spinner and pan tropical dolphins. The Agreement of the International Dolphin Conservation Program (AIDCP) was put into place to track this fishery and any dolphin moralities (IATTC 2003).

Eastern Pacific Ocean (EPO) longlines fisheries that capture yellowfin tuna also catch a number of other species of fish, including billfish and other tuna species, and sharks.Purse seine fisheries also catch a number of fish and shark species. The troll fishery catches small amounts of other tuna species and fish.

Other common bycatch species in the longline fishery include blue and silky sharks, indo-Pacific sailfish, dolphinfish and swordfish. Blue shark populations are currently healthy in the north Pacific region of the EPO but populations in the south Pacific appear to be in much worse condition. The current status of silky sharks, despite an assessment being conducted, is unknown in this region. The status of indo-Pacific sailfish is also uncertain. Swordfish populations are healthy in both the northern and southern region of the EPO {ISCSWG 2014}{IATTC 2013c}{IATTC 2014b}.

In the purse seine fishery (floating object), yellowtail, mahimahi, rainbow runner and wahoo are common bycatch species. Mahimahi and rainbow runner are also caught in the unassociated fisheries. Assessments have not been conducted on these species, so their status is unknown. Silky and oceanic white tips sharks, along with manta rays (unassociated) are also incidentally caught (Hall and Rowman 2013). No assessments of oceanic whitetip sharks or manta rays have been conducted. Oceanic whitetip sharks are prohibited from being retained and shark finning (5% rule) is prohibited (IATTC 2011c).

The gears used to capture tuna have no impact on bottom habitats.

Last updated on 29 Dec 2009

Under Resolution C-11-01 of IATTC for Conservation of Tuna in the Eastern Pacific Ocean Purse seiners over 182 metric tons carrying capacity ((IATTC size classes 4, 5 and 6) fishing for tunas in the Eastern Pacific Ocean shall cease fishing for 62 days from either (1) 29 July to 28 September; or (2) 18 November to 18 January 2012 during the current year (IATTC 2011).

IATTC Closures for purse seiners (IATTC 2011):
2011– 29 July to 28 September, or from 18 November to 18 January 2012.

2012– 29 July to 28 September, or from 18 November to 18 January 2013.

2013 – 29 July to 28 September, or from 18 November to 18 January 2014.