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I. Biological Description
Bigeye tuna (Thunnus obesus) is one of two
species known in Hawaii simply as ahi. Similar in
general appearance to yellowfin tuna (the other
species known as ahi), the bigeye may be recog-
nized by its plump body, its larger head and its
unusually large eyes.
Adult bigeye tuna are the deepest occurring of all tuna species, with the depth range of greatest
concentration at 150 to 250 fathoms. Smaller bigeye (20-30 pounds) may be encountered in shal-
lower waters in the vicinity of seamounts or floating objects, including fish aggregation buoys.
II. Of Special Interest For Buying/Distributing
Availability And Seasonality:
The availability of bigeye tuna in Hawaii has increased as a result of an
expansion of the domestic longline fleet and an extension of the fleet’s fishing range to as far as 800
nautical miles from port.
The peak in Hawaii’s landings of bigeye tuna occurs during the winter season (October-April), which
is the off-season for harvesting other tuna species.
Fishing Methods:
Bigeye tuna is harvested in Hawaii primarily by longline boats which set hooks at
the deep swimming depths of this species. Bigeye tuna is a minor component of the catch made by
the small-boat handline (ika-shibi) fleet off the island of Hawaii. It is rarely caught by trollers.
Distribution:
The longline catch of bigeye tuna is marketed primarily through the Honolulu fish
auction. Most of the handline (ika-shibi) catch is sold through the fish auction in Hilo and through the
intermediary buyers on the island of Hawaii. Virtually all bigeye is sold fresh.
Substitution:
Caught in deeper, cooler water, bigeye tuna typically has a higher fat content than
yellowfin and is preferred over yellowfin by more discriminating sashimi buyers. For less discriminat-
ing raw fish consumers, the two species are interchangeable. They are also interchangeable with
other tuna and marlin species for grilling purposes.
III. Of Special Interest For Preparation/Quality Control
Shelf Life And Quality Control:
Bigeye tuna has a longer shelf life than yellowfin tuna, and the natural
red flesh is slower to discolor after exposure to air. Longline-caught bigeye rarely develop the “burnt”
flesh problems often found in yellowfin taken on handline and trolling gear.
Some longline boats which catch bigeye tuna remain at sea for up to 10-12 days, but with proper
care, the fish will retain a high quality for over two weeks after capture (see Table 3). Although not as
Bigeye Ahi (Bigeye Tuna)