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Thunnus thynnushorse mackerel

By Michael Johnson

Geographic Range

Bluefin tuna are distributed throughout the Atlantic and Pacific Oceans in subtropical and temperate waters. In the western Atlantic Ocean, they are found from Labrador, in Canada, to northern Brazil, including the Gulf of Mexico. In the eastern Atlantic Ocean, they are found from Norway to the Canary Islands. In the western Pacific Ocean, they are found from Japan to the Philippines. In the eastern Pacific Ocean, they are found from the southern coast of Alaska to Baja California, Mexico. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Habitat

Bluefin tuna are marine fishes, they occupy both coastal and pelagic waters. They occupy depths from the surface to 1000 meters. They live in tropical, subtropical, and temperate waters. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

  • Range depth
    1000 (high) m
    3280.84 (high) ft
  • Average depth
    30 m
    98.43 ft

Physical Description

Bluefin tuna are the largest of the tunas. They have a long pointed head and small eyes. Bluefin tuna have two dorsal fins with a small space between them and short pectorial fins. Their anal fin begins far behind the second dorsal fin and they have three keels on their caudal peduncle. Bluefin tuna have a metallic blue color on the top half of their bodies and silver from the middle of their sides down to the bottom. Their first dorsal fin is yellow or blue and their second is red or brown. Their anal fin and finlets are yellow edged with black. Their central caudal keel is black. Bluefin tuna are usually between .5 and 2.0 meters in length. They weigh on average between 136 kg and 680 kg (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    136 to 680 kg
    299.56 to 1497.80 lb
  • Average mass
    250 kg
    550.66 lb
  • Range length
    .5 to 4.5 m
    1.64 to 14.76 ft
  • Average length
    2 m
    6.56 ft

Development

Bluefin tuna larvae hatch at 3.0 mm and have large heads, large jaws, and lack body pigmentation. They do have dorsal tail pigment. After hatching they grow 1 mm per day. The young are on average 5.80 mm after 10 days, 10.62 mm by 20 days, and 35.74 mm by 30 days after hatching. Growth is especially accelerated after 20 days after hatching, up to 2.10 mm/day. Young begin schooling with other species of tuna based on size. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Reproduction

Bluefin tuna form spawning aggregations. Males and females synchronously produce eggs and sperm (milt), resulting in mating among many individuals at the same time. This is also called broadcast spawning. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Bluefin tuna migrate to either the Gulf of Mexico or the Mediterranean and form spawning aggregations. Females lay up to 10 million eggs each spawning period. Males fertilize the eggs as they are produced by the females. Water temperatures during spawning are 24.8°C to 29.5°C in the Gulf of Mexico and 18.9°C to 21.1°C in the Mediterranean. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Bluefin tuna become sexually mature between the ages of 4 and 8 years. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

  • Breeding interval
    Bluefin tuna breed once yearly.
  • Breeding season
    Breeding occurs from April to June in the Gulf of Mexico and June to August in the Mediterranean.
  • Range number of offspring
    10,000,000 (high)
  • Range time to hatching
    1.5 to 4 days
  • Average time to hatching
    3 days
  • Range age at sexual or reproductive maturity (female)
    4 to 8 years
  • Average age at sexual or reproductive maturity (female)
    5 years
  • Range age at sexual or reproductive maturity (male)
    4 to 8 years
  • Average age at sexual or reproductive maturity (male)
    5 years

No parental care is provided for the young. (Agustin, et al., 2005; Figaro, 2005; Marinebio.org, 2005; Scott, 1997; Tudela, 2001)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning

Lifespan/Longevity

In the wild bluefin tuna are expected to live about 15 years. It is estimated that the longest lifespan known in the wild is between 20 and 30 years. Tuna caught and placed in captivity have short life spans because they are kept for a short period of time while they are fattened before harvesting. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

  • Range lifespan
    Status: wild
    30 (high) years
  • Typical lifespan
    Status: wild
    10 to 25 years
  • Average lifespan
    Status: wild
    15 years

Behavior

Bluefin tuna display schooling behavior based on size not species. It is not uncommon to see many different species of similarly sized tuna in a school together. Schools migrate north during summer months along the coast of Japan and the west coast of the United States. Trans Pacific migrations have been observed. Bluefin tuna have been known to cross the Atlantic Ocean in 60 days. Recent tagging data has shown that individual bluefin tuna frequently make several migrations from the eastern Atlantic to the western Atlantic and back again during the course of a year. Bluefin tuna can swim up to 72.5 kph. Because they are capable of high speeds, they are very powerful predators. They form feeding aggregations throughout the Atlantic and Pacific when it is not spawning season. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Home Range

The home rane of bluefin tuna is usually only limited to either the Atlantic Ocean or the Pacific Ocean. Individuals frequently migrate throughout the ocean in which they occur. For example, bluefin tuna have been observed to make several trips from the North American Atlantic coast to the European Atlantic coast and back again in a single year. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997)

Communication and Perception

Bluefin tuna perceive their enviroment and communicate through visual and chemical cues. They also have a well-developed lateral line system. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Scott, 1997)

Food Habits

Bluefin tuna chase down their prey using their ability to swim at very high speeds. They can also use modified filter feeding to catch small, slow moving organisms. They have also been known to eat kelp. They form feeding aggregations throughout the Atlantic and Pacific outside of the spawning season. Very little feeding occurs during spawning season. (Agustin, et al., 2005; Figaro, 2005; Gardieff, 2005; Jeffries, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Larvae feed on small organisms such as brine shrimp, other fish larvae, and rotifers. Juveniles also feed on small organisms until they become large enough to start feeding on small fish. The prey of adults include smaller fish, squid, eels, and crustaceans.

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans
  • echinoderms
  • other marine invertebrates
  • zooplankton

Predation

Predators of bluefin tuna include sharks, large predatory fishes, humans, marine mammals, including killer whales and pilot whales. Their anti-predator behaviors are schooling and the ability to make a fast escape. Their countershaded coloration makes them camouflaged in aquatic environments, their blue coloration dorsally makes them less visible from above and their light ventral coloration makes them less visible when seen from below. (Agustin, et al., 2005; Figaro, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Bluefin tuna are predators in their ecosystem and they are also a source of food for larger predators, including humans. They act as hosts for at least 72 parasites. These include: Euryphorus brachypterus, found in branchial cavities, Brachiella thynni, found on the fins, Pennella filosa, which inserts itself into the flesh of the fish, Pseudocycnus appendiculatus, found on the gill filaments, and Caligus bonito and C. productus which are found on the surface of the body and the wall of the branchial cavities.

They are also mutualists with other tuna species because tunas school in groups of similar sizes and mixed species, rather than groups of the same species. (Gardieff, 2005; Marinebio.org, 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Bluefin tuna are a popular sport fish. A very large and profitable industry has developed around bluefin tuna. They are a popular food item worldwide. (Agustin, et al., 2005; Miyashita, et al., 2001; Scott, 1997; Tudela, 2001)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Tuna fishing practices often result in harm to other species, including dolphins and sea turtles. There are potential health risks to humans that come from consuming large amounts of tuna due to mercury contamination in their flesh. Mercury contamination can result in damage to the nervous system, digestive system, respiratory system and kidneys. It can also have damaging effects on the male reproductive system and on developing fetuses. Mercury contamination is usually the result of bioaccumulation of toxins in water as a result of human activities. (Hightower and Rider, 2005; Jeantheau, 2004; Marinebio.org, 2005; Shwartz and Peterson, 2005)

Conservation Status

Many are concerned that bluefin tuna could easily become endangered due to high demand as a food source and resultant overfishing. Because bluefin tuna are migratory, they are often fished in international waters which caused the International Commission for the Conservation of Atlantic Tunas to be created in 1966. The ICCAT proposes management methods, conservation methods, and conducts reseach. Also in 2001 helicopter spotting was banned in the Mediterranean to try to control the amount harvested. Bluefin tuna cannot be breed in captivity. Bluefin tuna farms are not real farms. Tuna are instead caught and fattened rapidly, then processed. (Agustin, et al., 2005; Figaro, 2005; Miyashita, et al., 2001; Scott, 1997)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Michael Johnson (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

macroalgae

seaweed. Algae that are large and photosynthetic.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Agustin, L., A. Sampang, S. Luna. 2005. "Species Summary" (On-line). Accessed October 12, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=147.

Figaro, L. 2005. "MEDITERRANEAN BLUEFIN TUNA ON ENDANGERED LIST?" (On-line). Accessed October 18, 2005 at http://www.spc.int/coastfish/News/Fish_News/100/NIAR_100_3.htm.

Gardieff, S. 2005. "Bluefin Tuna" (On-line). Accessed October 14, 2005 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/BluefinTuna/BluefinTuna.html.

Hightower, J., R. Rider. 2005. "NRDC: Mercury Contamination in Fish" (On-line). NDRC. Accessed December 01, 2005 at http://www.nrdc.org/health/effects/mercury/effects.asp.

Jeantheau, M. 2004. "Mercury in Fish" (On-line). Grinning Planet. Accessed December 01, 2005 at http://www.grinningplanet.com/2004/08-10/mercury-in-fish-article.htm.

Jeffries, B. 2005. "Southern Bluefin Tuna" (On-line). Accessed October 16, 2005 at http://www.sardi.sa.gov.au/pages/aquafin/southern_bluefin_tuna_industry.htm.

Marinebio.org, 2005. "Atlantic Bluefin Tuna" (On-line). Accessed October 12, 2005 at http://marinebio.org/species.asp?id=236.

Miyashita, S., Y. Sawada, T. Okada, O. Murata, H. Kumai. 2001. "Morphological development and growth of laboratory-reared larval and juvenile Thunnus thynnus" (On-line). Accessed October 12, 2005 at http://www.findarticles.com/p/articles/mi_m0FDG/is_4_99/ai_81790014.

Scott, S. 1997. "Ocean Watch" (On-line). Accessed October 13, 2005 at http://www.susanscott.net/OceanWatch1997/sep01-97.html.

Shwartz, M., K. Peterson. 2005. "Electronic tags reveal transatlantic migrations and breeding grounds of Atlantic bluefin tuna" (On-line). Accessed December 02, 2005 at http://www.stanford.edu/dept/news/pr/01/tunastudy822.html.

Tudela, S. 2001. "Tuna Farming in the Mediterranian: The Coup de grace to a Dwindling Population" (On-line). Accessed October 17, 2005 at http://72.14.203.104/search?q=cache:x9DyDZgfi00J:www.wwf.no/english/aquaculture/wwf_medpo_tuna_farming_report.doc+bluefin+tuna+captivity+lifespan&hl=en.

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