Bigeye Tuna

Thunnus obesus

Allen Shimada/NOAA fisheries

The Science


This fish's blood has a counter-current heat exchange system that allows it to stay warm in colder, deeper water

big eye

Taxonomic description

  • Has a large, robust body that is slightly compressed from side to side. [1]
  • Back is metallic dark blue, lower sides and belly is whitish, yellow fins and lateral iridescent blue band runs along sides of live individuals. [1]
  • Distinguished from yellowfin tuna by its bigger eyes and black-edged finlets. [1]
  • Usually weighs 20-200 lbs. [2]


  • Found in tropical and temperate waters of the Atlantic, Indian, and Pacific Oceans. [2]

Life history

  • Lives seven to nine years and matures between three and four years. [2]
  • Spawns year-round in tropical waters, seasonally in temperate waters. [2]
  • Releases 3-6 million eggs during spawning! [2]
  • Eggs have oily coatings in order to float until hatched, about 24 hours after fertilization. [2]


  • Migratory, and will school with other tuna species at ocean surface. [2]
  • Moves to deeper waters at night, has eyes adapted to low light levels and can regulate body temperature. [2]
  • Feeds on fishes, cephalopods, and crustaceans. [1]
  • Preyed on by larger tuna, billfish, toothed whales, and sharks. [2]

The Fishery


After a historic low level in 2004, Eastern Pacific bigeye tuna populations have been increasing and are now above target population levels!

big eye
Tuna Harbor Dockside Market/Facebook

Seasonal availability

  • Available year-round. [3]

Regulatory and management authority

  • Internationally overseen by the Inter-American Tropical Tuna Commission (IATTC) and the Western and Central Pacific Fisheries Commission (WCPFC). [3]
  • Along the Pacific West Coast, the fishery is overseen by NOAA fisheries and, as established by the Magnuson-Stevens Act, the Pacific Fishery Management Council  through the West Coast Highly Migratory Species Fisheries Management Plan. [3,4]
  • As established by the Marine Life Management Act, the California Department of Fish and Wildlife (CDFW) collects data on this fishery through the Pelagic Fisheries and Ecosystem Program. [5,6]

Gear type

  • Caught by purse seine, longline and handlines, and hook-and-line. [3]

Status of the fishery

  • Stock is considered vulnerable by IUCN, but is monitored closely by governing authorities. [3]

Potential ecosystem impacts

  • Fishing gear rarely contacts seafloor, so there are minimal habitat impacts. [3]
  • To minimize the impact of bycatch, management measures, training programs, and observer programs are required for American fishermen. [3]

The Seafood


Although "Ahi" refers to both bigeye and yellowfin tuna, bigeye has a higher fat content and is typically preferred by sashimi lovers!


Edible portions

  • Typically only the meat is consumed, but the rest of the fish can also be utilized. [2]

Description of meat

  • Firm and moist with a mild, meaty flavor and reddish-pink color that has large flakes when cooked. [2]

Culinary uses

  • Enjoy it raw, baked, broiled, grilled, sautéed, or smoked! [2]
  • For a tuna nigiri recipe, visit Izzy Cooking. [7]
  • For a Spanish tuna meatball recipe, visit Luxe Gourmets. [8]

Nutritional information

  • Information for 100g of bigeye tuna shown on table at the right. [3]
  • Bigeye tuna is a good source of Omega-3! [3]

Toxicity report

  • As bigeye tuna may have mercury, recommended servings depend on age and gender. [3]

Seasonal availability

  • Available year-round. [3]


[1] Luna, S.  Fishbase. n.d. Thunnus obesus. Web. Accessed 4 February 2021.

[2] FishChoice. 2020. Bigeye Tuna. Web. Accessed 4 February 2021.

[3] Fishwatch. 2020. Pacific Bigeye Tuna. Web. Accessed 4 February 2021.

[4] Fishery Management Plan for U.S. West Coast Fisheries for Highly Migratory Species. 2018. Pacific Fishery Management Council. Web.…. Accessed 24 August 2020. 

[5] Marine Life Management Act. n.d. California Department of Fish and Wildlife. Web. Accessed 24 August 2020. 

[6] Overview of the Pelagic Fisheries and Ecosystems Program. n.d. California Department of Fish and Wildlife. Web. Accessed 9 December 2020. 

[7] izzy cooking. 2020. Tuna Nigiri (How to make tuna sushi). Web. Accessed 4 February 2021.

[8] Matsumoto, M. Luxe Gourmets. 2015. Bigeye Tuna Albondigas. Web. Accessed 4 February 2021.

[9] Hawaii Seafood. 2015. Bigeye Tuna (Ahi). Web. Accessed 5 February 2021.

[10] Shimada, A. NOAA fisheries. 2006. Thunnus_obesus Longline fishing research on the NOAA Ship OSCAR ELTON SETTE. Bigeye tuna. Digital image. Web.…. Accessed 5 February 2021.

[11] bexlloyd. iNaturalist. 2017. Digital image. Web. Accessed 12 February 2021. 

[12] Tuna Harbor Dockside Market. Facebook. 2021. Digital image. Web. Accessed 5 February 2021.

[13] McCullum, J. flickr. 2016. Tuna the way they like it. Digital image. Web. Accessed 12 February 2021.