Tuna, southern bluefin
(Castelnau, 1872); SCOMBRIDAE FAMILY; also called Japanese Central Pacific
A species of the southern ocean found worldwide from 30?S to about 50?S
latitude occurring in oceanic to coastal waters below thermoclines. Southern
bluefin are commonly found off the southern and eastern coasts of Australia
and New Zealand.
This pelagic and seasonally migratory species has been studied quite extensively
in Australian waters due to its commercial importance. They spawn in the
eastern Indian Ocean with one and two year old fish appearing off Western
Australia in summer. Three and four year olds appear off Southern Australia
in summer and New South Wales in winter. The migratory route from the Indian
Ocean to the Pacific splits into two routes off southern Tasmania. Fish
move either to northern New Zealand via South Island or up the Australian
They closely resemble the Atlantic bluefin (Thunnus thynnus), and were
once thought to be the same species. The difference is the number of gill
rakers. The southern bluefin has a total of 31 40 on the first arch while
the Atlantic bluefin has a total of 34 43. Both have in common striations
on the ventral surface of the liver, short pectoral fins that do not reach
to the interspace between the first and second dorsal fins, and moderate
second dorsal and anal fins that are never elongated like those of the
yellowfin tuna (T. albacares). The finlets are dusky yellow edged with
black. It is the only species of Thunnus in which the caudal keels are
bright yellow except in fish larger than 150 lb (68 kg) where the caudal
keels tend to be darker.
They travel in schools of similar sized fish. Their diet consists of a
variety of crustaceans, cephalopods, and fish including anchovies and pilchards.
The most popular method of catch this powerful, hard fighting fish is
trolling. It can also be taken from boats or from the shore using live
scombroid fishes (mackerels and little tunas) for bait. It is rarely taken
on dead baits. Hooked fish are prone to fast surface runs and deep sounding.
They are excellent both as a sport fish and as table fare