While bigeye tuna quality is difficult to determine due to subjective criteria, number 2 quality is usually adequate for the U.S. market while Number 1 quality is primarily exported to Japan. Fresh and frozen bigeye is sold to foodservice operators as loins and steaks. Early fall is a good time to buy fresh bigeye tuna, as demand drops and landings are normally still quite good. Frozen bigeye tuna is commonly treated with carbon monoxide or tasteless smoke to prevent the red color of the fish from going brown. If abused, carbon monoxide can be used to enhance the color of lower grade bigeye. However, fresh bigeye loins and steaks are rarely treated with carbon monoxide to maintain color.
Key sustainability sourcing notes for bigeye tuna based on combining landings data from 2016-17 and the most recent Seafood Watch assessments, as of October, 2019, are as follows:
~1% of global landings and ~90% of U.S. landings meet a Seafood Watch "Good Alternative (yellow)" rating (deepset longline-caught from Hawaii Eastern Pacific Ocean and pelagic longline-caught from Hawaii West Central Pacific)
~90% of global bigeye tuna landings meet a Seafood Watch "Avoid (red)" rating
~10% of global bigeye tuna landings are unrated/unknown
% of landings of bigeye tuna stocks is W. Central Pacific ~35%, E. Pacific ~25%, Indian O. ~20%, and Atlantic O. ~20%
Global bigeye tuna landings in 2017 saw a decrease of ~4% compared to 2016 and a decrease of ~6% compared to 2014
Bigeye tuna are similar in appearance to yellowfin tuna, as both have yellow fins and metallic blue bodies; however, the bigeye’s eyes are larger and their finlets have black edges. Similar to bluefin tuna, bigeye are able to change their internal body temperature depending on their location in the water column.
Bigeye tuna grow quickly, reaching lengths of six to seven feet (two meters). They live seven to nine years and reach maturity between three and four years. Although bigeye can weigh up to 400 lbs., they are typically 20-200 lbs. in commercial landings. In tropical waters, bigeye tuna spawn year-round. In cooler waters, bigeye tuna spawn seasonally. They release between three and six million eggs during spawning, which are found near the surface of the water. The eggs have an oily coating, allowing them to easily float until hatched, about 24 to 30 hours after fertilization.
Bigeye tuna reside near the surface during the night, and move to deeper waters during the day to hunt. Their notably big eyes are adapted to low light levels, as they spend most of their time in low light environments. Their blood has a counter-current heat exchanging system, and high oxygen affinity and capacity for oxygen offloading, allowing bigeye tuna to maintain a comfortable body temperature and a regulated metabolic rate in cold and oxygen deficient waters. Bigeye tuna’s preference for feeding in deeper water allows for competition avoidance with other tunas that often live and hunt in the same area. They feed near the top of the food chain, preying on fish, crustaceans, and squid. They are prey to top predators, including larger tuna, billfish, toothed whales, and sharks.
Bigeye tuna are found throughout the tropical and temperate waters of the Atlantic, Indian, and Pacific Oceans. There are four main stocks of bigeye: Western and Central Pacific Ocean, Eastern Pacific Ocean, Atlantic Ocean, and Indian Ocean. In the western Atlantic, they are found from Nova Scotia to Brazil (their range does not extend into the Mediterranean). Off the US Pacific, they are found from California to Hawaii, including US Pacific Island Territories and the high seas. While their range extends from 55-60° N and 45-50° S, larvae are found in more tropical waters and as they grow into juveniles and adults, will move into more temperate waters. Eggs, larvae, juveniles, and adults are pelagic. Bigeye are highly migratory and are known to make extensive seasonal migrations throughout the world’s oceans. Juveniles and small adults will school at the ocean surface – sometimes with yellowfin and skipjack tuna – especially in warm waters. They are often associated with floating objects. Adults will also form schools, but generally in deeper, subsurface waters. Bigeye also tend to school near seamounts and submarine ridges. They are known to dive deeper than other tropical tunas to depths of about 800 feet (244 meters). Bigeye can be found in temperatures ranging from 54 to 84 degrees Fahrenheit (13 to 29 degrees Celsius), but their preferred, optimum range is between 63 and 72 degrees Fahrenheit (17 and 22 degrees Celsius).
Science & Management
Little is known about the ecology of Atlantic bigeye stocks, and much of what has been published has been taken from fisheries data and studies on the Pacific Ocean and Indian Ocean stocks. The International Commission for the Conservation of Atlantic Tunas (ICCAT) compiles fishery statistics, coordinates research, and develops science-based management advice. Their Atlantic Ocean Tropical Tuna Tagging Programme (AOTTP) will spend five years (starting in 2015) tagging bigeye, skipjack and yellowfin tuna in tropical Atlantic waters. The data will be maintained by ICCAT and used to improve stock assessment parameters, as well as contribute to food security and economic growth of the Atlantic coastal states internationally by ensuring sustainable management.
Atlantic bigeye tuna are currently evaluated as a single stock; however, depending on their migratory behavior and habitat use, they could be managed as two separate stocks in the future. In 2014, researchers at NOAA and the University of Massachusetts Amherst tracked bigeye tuna throughout the Atlantic. In order to better characterize the relationship between their behavior and environmental factors, researchers studied the role that location, temperature, light penetration, and water pressure play in impacting their movements throughout their range. The need for long-term, seasonal data is necessary to develop effective management strategies.
A 2010 study published by NOAA found that tuna and billfish populations are more vulnerable to fishing pressure because of shrinking habitat. An expanding hypoxic zone (an area of low oxygen) in the Atlantic Ocean is decreasing oxygen-abundant habitats, forcing the species into shallower waters where they are more vulnerable to predators and fishing. The hypoxic zones occur naturally in tropical and equatorial oceans; however, they are going to continue expanding and increasing in number as sea temperatures rise. Fish that prefer these habitats will move to shallower areas, increasing their catch rates, and giving the appearance of greater abundance than actually exists, thus affecting population and stock assessments. Higher water temperatures absorb less oxygen, and climate change will increase the expansion of hypoxic zones in the world’s oceans.
NOAA’s Pacific Islands Fisheries Science Center (PIFSC) has developed the Pacific Tuna Tagging Project (PTTP) in 2006 to tag and release bigeye, skipjack, yellowfin, and tuna throughout the western and central Pacific Ocean. The goal of the PTTP is to improve stock assessments, and better understand the status of the stocks and tuna movements.
Researchers at the Ocean Science Series of the PEW Environment Group found in 2011 that increasing the use of fish aggregating devices (FADs) changes the species composition of tuna catches. Vessels targeting skipjack tuna using FADs also catch a large amount of juvenile yellowfin and bigeye tuna. This impacts the biology and ecology of bigeye, skipjack, and yellowfin tuna, as younger individuals are being caught and the population is not able to replenish itself.
NOAA Fisheries and NOAA Fisheries’ Atlantic Highly Migratory Species (HMS) Division are responsible for managing the US Atlantic bigeye tuna fishery under the Consolidated Atlantic Highly Migratory Species Fishery Management Plan. Amongst measures outlined in the plan include: permit requirements, gear restrictions, time and area closures, and minimum size limits. All federal management measures for Atlantic tunas apply to US state waters (except in Maine, Connecticut, and Mississippi). The US harvest of bigeye makes up a small proportion of the total worldwide catch (less than one percent).
Like other tunas, bigeye are highly migratory and cross international boarders and the high seas. As such, their management requires international cooperation. The United Nations Law of the Sea indicates that the management of HMS be carried out through Regional Fishery Management Organizations (RFMOs). RFMOs are the only legally mandated fishery management body on the high seas. The RFMO responsible for the management of Atlantic tunas, as well as other Atlantic HMS, is the International Commission for the Conservation of Atlantic Tunas (ICCAT). ICCAT is made up of 51 contracting parties including the United States, Canada, Japan, China, Russia, and the United Kingdom. Among management measures ICCAT outlines are:
A total allowable catch (currently set at 65,000 tonnes) allocated between members as well as sharing arrangements for other countries; Time and area closures; Size limits; Effort controls; and, Monitoring, reporting, and inspection programs.
Between 2011 and 2015 bigeye tuna account for roughly 16 percent of the total tuna catch in the Atlantic. In 2015, purse seine and pole-and-line vessels accounted for about 37 and 15 percent of the total Atlantic bigeye tuna catch respectively. According to the last stock assessment conducted by the ICCAT Standing Committee on Research and Statistics in 2015, the stock is estimated to be overfished and overfishing is occurring. NOAA Fisheries uses conservation and management measures adopted by ICCAT, along with their own research, to set regulations for the US Atlantic skipjack fishery.
NOAA Fisheries and the Pacific Fishery Management Council manage the skipjack tuna fishery on the US West Coast under the Fishery Management Plan (FMP) for US West Coast Fisheries for Highly Migratory Species. Management measures outlined within the FMP include: permit requirements, catch recording, gear restrictions (no longlines are allowed within 200 miles of the coast, etc.), and observer coverage (100 percent for longline vessels and large purse seine vessels). In Hawaii and Pacific Island territories, NOAA Fisheries and the Western Pacific Fishery Management Council manage the skipjack tuna fishery in the US Pacific under the Fishery Ecosystem Plan for Pelagic Fisheries of the Western Pacific. Management measures outlined in this FMP include: permit requirements and limits, gear restrictions, area closures (to protect endangered Hawaiian monk seals), and a vessel monitoring system and observer coverage (100 percent for longline vessels operating in Hawaii and America Samoa and purse seine vessels operating under the South Pacific Tuna Treaty).
The Inter-American Tropical Tuna Commission (IATTC) is the RFMO in charge of managing international bigeye tuna stocks in the Eastern Pacific Ocean (EPO). Composed of over 20 different nations including the United States, Canada, China, Belize, Costa Rica, and Mexico, IATTC sets management measures that all member nations must adhere to. As of 2015, the majority of bigeye tuna in the EPO are caught using purse seine (62 percent of the total catch) and longline gear (38 percent of the total catch). In the EPO, IATTC has set management measures for the purse seine and longline fisheries which include time and area closures, 100 percent observer coverage on large vessels, annual catch limits, and requirements that all vessels in the purse seine fishery retain all tuna caught. Any purse seine vessel operating in the EPO must also operate in accordance to the International Dolphin Conservation Program, which works reduce bycatch of dolphins and undersized tuna. Between 2011 and 2015 bigeye account for 16 percent of the total average tuna catch in the EPO. According to the updated 2016 stock assessment EPO bigeye are currently overfished; however, overfishing is not taking place.
The Western and Central Pacific Fisheries Commission (WCPFC) is the RFMO in charge of managing international bigeye stocks in the Western and Central Pacific Ocean (WCPO). WCPFC is composed of over 25 member countries including Australia, China, New Zealand, Indonesia, Japan, France, the United States, and the Republic of Korea. Among measures member nations adhere to are:
A three-month prohibition on setting fish aggregating devices (FADs) in exclusive economic zones (EEZs) and high seas between 20 degrees north and 20 degrees south (additionally each member must choose between extending the FAD closure to a total of four months or limit the annual number of FAD sets made by its vessels as outlined in specified reference period);
Coastal states must reduce purse seine effort to 2010 levels (if they are a member country of the Parties to the Nauru Agreement (PNA);
If they are not a participant in the PNA they must reduce purse seine effort to average levels between 2001 and 2004;
Purse seine vessels for other countries cannot increase;
A FAD management plan to reduce capture of juvenile tunas and prepare for FAD closures;
Annual compliance monitoring requirements and 100 percent observer coverage for purse seine vessels on the high seas, in waters under the jurisdiction of one or more coastal States, or for vessels operating between 20 degrees north and 20 degrees south (unless operating exclusively in their EEZ) ; and,
Prohibition of discarding any tuna catch between 20 degrees north and 20 degrees south.
PNA member countries have also agreed to additional management measures including: a regional fishing vessel register, high seas pocket area closures, FAD prohibitions during set times, and a vessel day scheme.
The majority of the WCPO bigeye catch is caught using purse seine and longline gears. From 2011 to 2015 bigeye tuna accounted for an average of six percent of the total tuna catch from the WCPO. Despite management measures, the WCPO bigeye stock is considered to be overfished and measures in place are considered to be insufficient to end overfishing.
The Indian Ocean Tuna Commission (IOTC) is the RFMO charged with managing bigeye tuna in the Indian Ocean. There are currently 31 members (majority are nation states) in the IOTC. There are no species-specific conservation measures established by the IOTC for IO bigeye tuna; however, member countries must have: reference points and harvest control limits, bycatch mitigation strategies (particularly with sea turtles, juvenile tunas, and sharks), and observer coverage (IOTC requires at least five percent of vessels have an observer). Additionally, IOTC members must have a FAD management plan that includes information on the fleet, number of drifting FADs, logbooks, and monitoring and review plans. IOTC member nations require all tuna caught by purse seiners be retained and landed, and encourages retention of other non-targeted finfish. Member countries are also required to record and report catch and effort data by species and gear type. From 2011 to 2015 bigeye tuna accounted for roughly 11 percent of the total tuna catch in the IO. According to a 2016 stock assessment, overfishing is not occurring and the stock is not overfished.
Bigeye tuna, also called ahi, reproduces quickly. Fast and highly migratory, bigeye tuna can be found in the Pacific, Atlantic and Indian Oceans. This tuna is also long-lived but growth rates vary by population and ocean. Seafood Watch reports that in the Indian Ocean bigeye populations are healthy and fishing mortality rates are low. In the Atlantic, bigeye tuna populations are fluctuating around healthy levels, but have been below these levels in recent years, according to a Seafood Watch report. Despite their wide distribution and abundance, bigeye tuna in the Pacific declined over the past several decades due to intense fishing pressure. Bigeye are overfished in the eastern Pacific. In the western and central Pacific, bigeye populations are not healthy and fishing pressure is too high.
Habitat impacts (Wild)
Bigeye tuna are caught primarily with longlines, which are set off the bottom so they have minimal habitat impacts. Bigeye are also caught with troll lines, pole-and-lines, gillnets and purse seines. Purse seines usually have little contact with the bottom, although fish aggregating devices can be anchored there. Trolling and pole-and-line fishing also have minimal impact on bottom habitats, according to the Seafood Watch.
The longlines and purse seines targeting bigeye tuna also capture non-targeted fish such as other tunas, billfish and bony fish as well as sharks, seabirds and threatened sea turtles. Longliners in particular result in high bycatch rates. Purse seiners using fish aggregating devices can inadvertently attract non-targeted fish and sometimes protected species. Juvenile and small adult bigeye tuna bycatch is high for the skipjack and yellowfin purse seine fisheries. Bigeye tuna caught by troll or pole-and-line, particularly in the U.S. Atlantic, results in some of the least bycatch.
Bigeye tuna’s wide distribution requires effective international management, which has not been successful so far. Despite measures that include reporting requirements, observer programs, bycatch reduction, vessel monitoring, and fishing capacity limits, conservation goals are not being met in every region.
In the Atlantic, bigeye tuna is managed by International Commission for the Conservation of Atlantic Tunas (ICCAT). The National Marine Fisheries Service, and Fisheries and Oceans Canada manage tuna in U.S. and Canadian waters. The Inter-American Tropical Tuna Commission manages bigeye and other tuna species in the eastern Pacific.
There is a multi-annual management plan in place for bigeye in the eastern Pacific. However, many of ICCAT’s measures for the longline tuna fisheries do not meet best practice requirements, and scientific advice has not always been followed when setting those measures, according to Seafood Watch. Purse seines have 100% observer coverage but there are no harvest control rules or target reference points. For state waters in the western and central Pacific, the state of Hawaii manages tuna. In U.S. federal waters, the Western Pacific Regional Fishery Management Council (WPRFMC) manages them. Seafood Watch considers measures in this region to be moderately effective. The Western and Central Pacific Fisheries Commission (WCPFC) also manages bigeye. While some purse seine specific management measures have been introduced in that region, the success is not known.
Indian Ocean bigeye tuna are managed by the Indian Ocean Tuna Commission, and by the Ministry of Fisheries and Aquatic Sciences in Sri Lanka. Seafood Watch gave management in that region a red rating.