Southern bluefin tunaSBF

© J. Yick, taken in Tasmania, Australia, ~ 90 cm FL
© J. Yick, taken in Tasmania, Australia, ~90 cm FL

Characteristic features:

  • Large median keel with 2 smaller keels on either side of caudal peduncle
  • 31–34 gill rakers on first gill arch
  • 8–10 dorsal and 7–9 anal fins
  • Interpelvic process with 2 flaps
  • Pectoral fins short, not reaching beyond interdorsal space
  • Caudal-peduncle keel yellow in adults
  • Ventral surface of liver striated, lobes roughly equal in length (Fig. 1)

Colour:

Dark blue to black above, silvery white sides and below. A series of silvery white vertical lines alternating with vertical rows of dots, appearing only in fresh specimens and more prominently in younger fish. First dorsal fin yellow or blueish. Anal fin and finlets dusky yellow and edged with black; caudal-peduncle keel yellow in adults.

Size:

Up to 225 cm FL and up to 200 kg in weight.

Distribution:

Throughout cool-temperate waters of the Southern Ocean for most of its life. Extends to warmer waters as far northwest as Indonesia during the spawning season.

View FAO distribution map

Habitat:

Pelagic and oceanic. Usually found in waters between 5–20 °C, but also in waters over 20 °C during spawning season. Found at depth range of 50–2,743 m.

Biology:

A highly migratory species forming schools. Feeds on a variety of fish, crustaceans and salps. Length at first maturity is estimated at 120–130 cm FL, with 50% of individuals becoming mature at 152 cm FL. Age at first maturity estimated between 8 and 11 years. Maximum age estimates vary, ranging from 20 to 40 years.1,2

Indonesian fisheries:

Caught primarily by longlining.

Similar species:

Thunnus alalunga
Albacore tuna
Thunnus alalunga differs in having very long pectoral fins extending to second dorsal finlet (vs. short never reaching interdorsal space); white/silver horizontal to oblique, incomplete stripes present in stressed live, and freshly dead specimens only (vs. white/silver vertical, irregularly spaced, often broken or incomplete stripes present in stressed live specimens only); 25–31 gill rakers on first gill arch (vs. 31–34) and a dark coloured median keel (vs. yellow in adults).

 

Thunnus albacares
Yellowfin tuna
Thunnus albacares
Thunnus albacares differs in having moderately long pectoral fins, not reaching posterior of second dorsal-fin base (vs. short, never reaching interdorsal space); white/silver body markings in regularly spaced, vertical lines and alternating lines of spots in a ‘chevron’ pattern (vs. a series of white/silver irregularly spaced, often broken or incomplete vertical stripes present in stressed live specimens only, otherwise dark above, metallic silver below); ventral surface of liver not striated, right lobe elongate (vs. striated, lobes roughly equal in length); 26–34 gill rakers on first gill arch (vs. 31–34) and a dark coloured median keel (vs. yellow in adults).

 

Thunnus obesus
bigeye tuna

Thunnus obesus

Thunnus obesus differs in having a greater head length and depth (vs. smaller) and larger eye diameter (vs. smaller) for a given FL; pectoral fins very long, tips tapering to a thin flexible point (in adults) (vs. short, not reaching beyond interdorsal space); a series of white/silver body markings in irregularly spaced vertical sometimes broken lines (vs. white/silver irregularly spaced, often broken or incomplete vertical stripes present in stressed live specimens only, otherwise silver/white below); 23–31 gill rakers on first gill arch (vs. 31–34) and a dark coloured median keel (vs. yellow in adults).

 

Thunnus orientalis
Pacific bluefin tuna
Thunnus orientalis differs in having a series of white/silver markings as vertical lines and alternating lines of spots, mostly confined to lower portion of body (vs. white/silver irregularly spaced, often broken or incomplete vertical stripes present in stressed live specimens only, otherwise silver/white below) and a grey median keel (vs. yellow in adults).

 

Thunnus tonggol
Longtail tuna
Thunnus tonggol differs in having longer pectoral fins, not reaching origin of second dorsal fin (vs. short, not reaching beyond interdorsal space); posterior portion of body (from deepest point to caudal peduncle) long relative to FL (vs. moderate); horizontal rows of white/silver elongate spots on belly (vs. white/silver irregularly spaced, often broken or incomplete vertical stripes present in stressed live specimens only, otherwise silver/white below); 19–27 gill rakers on first gill arch (vs. 31–34) and a dark coloured median keel (vs. yellow in adults).

External inks:

FishBase
The IUCN Red List of Threatened SpeciesTM

References

1.
Collette BB, Nauen CE. FAO species catalogue. Volume 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. 1983.
2.
Gunn JS, Clear NP, Carter TI, Rees AJ, Stanley CA, Farley JH, et al. Age and growth in southern bluefin tuna, Thunnus maccoyii (Castelnau): direct estimation from otoliths, scales and vertebrae. Fisheries Research. 2008;92(2):207–20.