SOUTHERN BLUEFIN TUNA (Thunnus maccoyii)


Southern Bluefin Tuna: The Ultimate Fisherman’s Guide

There’s nothing quite like watching a big southern bluefin ghost up behind your spread, tracking the lure with that eerie calm, before exploding in a detonation of whitewater. Then comes the chaos—rods buckling, reels screaming, and line vanishing at blistering speed as that barrel dives deep into cobalt water. It’s raw power, pure adrenaline, and the kind of moment that keeps you thinking about the next trip before the boat even hits the ramp.

Southern Bluefin Tuna (SBT) is one of the most powerful, fast-swimming pelagic fish found in the southern oceans. It’s highly sought after for its fatty, rich, red meat, making it a top-tier sashimi-grade fish, especially in Japan, where it commands premium prices. Whether you’re targeting them for sport or commercial fishing, understanding their biology, migration patterns, and best fishing techniques will give you the edge.

All tackle world record 

173.6kg caught near White Island, New Zealand by Charles Baty on 07 August 2022.


Biology & Identification

Physical Features

  • Shape: Almost round in cross-section, with a bullet-like body designed for speed.
  • Fins: The first dorsal fin folds into a groove, reducing drag. Small finlets run between the second dorsal fin and tail, and between the anal fin and tail.
  • Tail: Features a caudal keel stabilizer for better swimming efficiency.
  • Color: Dark metallic blue when fresh from the water, with silver-white flanks. The finlets near the tail are yellow-edged with black, and the caudal keel is bright yellow in smaller fish, darkening in larger specimens.
  • Size: Can grow up to 2.5m long and weigh over 400kg.

Speed & Hunting Ability

Like other migratory tunas, SBT can maintain a body temperature up to 10°C higher than the surrounding water. This allows them to make explosive bursts of speed when chasing prey, making them one of the ocean’s most formidable hunters.

Diet

  • SBT hunt in schools of similar-sized fish and feed on:
  • Squid
  • Anchovies
  • Sauries
  • Pilchards
  • Other small fish and crustaceans

Where to Find Them & Migration Patterns

Australia

SBT are commonly found in southern Australian waters, particularly in the Great Australian Bight and off Tasmania. Their migration follows seasonal patterns:

  • 1-2 year-olds appear off Western Australia in summer.
  • 3-4 year-olds appear off Southern Australia in summer and New South Wales in winter.
  • Their migration splits near southern Tasmania, with some heading north to New Zealand via the South Island, while others move up the Australian coast.

New Zealand

The best New Zealand fishing grounds for SBT are off the West Coast of the South Island, particularly in Fiordland and the Hokitika Trench.

  • Commercial season runs March to September.
  • Schools occasionally seen on the surface in summer, chasing squid and baitfish.

Fishing Seasons

  • Australia: Best time to catch wild SBT is December to April, when they gather near the surface along the southern coast.
  • New Zealand: Best time is March to September, with peak activity in deep offshore waters.

Fishing Methods for Southern Bluefin Tuna

1. Trolling Lures (Most Common & Effective Method)

Trolling is the go-to technique for targeting SBT in offshore waters.

  • Trolling Speed: 5.5-6.5 knots is ideal.
  • Leader Choice: Use fluorocarbon leaders (200lb) to prevent chafing.
  • Strike Strategy: Keep the boat moving forward when a lure is struck—this often leads to multiple hook-ups.


2. Finding the Fish

  • Bird Activity: Watch for mollymawks and shearwaters circling or diving—this signals feeding tuna.
  • Bait Schools: If you spot anchovies, sauries, or pilchards on your sounder, tuna won’t be far behind.
  • Whales & Dolphins: These indicate food in the area, meaning tuna will likely be nearby.

3. Drift Fishing with Fillet Baits

Drift fishing is effective when targeting big bluefin in deep waters.

Best Baits:

  • Hoki fillets, squid, pilchards.

Burley Trail: Set up a burley trail to attract tuna to the boat.

Depth: Drop baits deep where tuna are feeding.

4. Live Bait Fishing

Live baiting is highly effective for targeting big bluefin.

Best Live Baits:

  • Mackerel, small Tuna, Squid, Koheru.

Rigging: Use circle hooks for better hook-ups.

Depth: Drop live baits deep or slow-troll them near bait schools.

6. Key Locations in New Zealand

  • Waihau Bay, East Cape – Deep water close to shore, ideal for trailer boats.
  • Whakatane & Tauranga – Target tuna east of White Island and Rangatira Knoll.
  • Whangamata, Tairua & Whitianga – Best spots near Mayor Knolls, Alderman Knoll, and Mercury Knoll.

Commercial Fishing & Ranching

  • Wild Catch: Purse seine and longline fishing methods are used.
  • Ranching (Sea-Pen Farming): Over 90% of wild-caught juveniles are transferred live to sea pens in Port Lincoln, South Australia, where they’re fattened up before being sold.
  • New Zealand Commercial Fishing: The Solander Fishing Company catches about 300 tonnes annually, using longlines on both the East and West Coasts.

Threats & Conservation

Overfishing & Population Decline

Southern Bluefin Tuna is now classified as Critically Endangered on the IUCN Red List due to overfishing. Their numbers have declined significantly since the 1970s, making sustainable fishing practices more important than ever.

Sustainable Fishing Practices

  • Catch limits help manage wild populations.
  • Ranching (sea-pen farming) allows for controlled growth while reducing pressure on wild stocks.
  • Tagging & monitoring programs track migration and population health.

Why They’re Worth the Effort

Sport Fishing Challenge

SBT are hard fighters, known for fast surface runs and deep dives when hooked. On lighter lines, battles can last several hours, making them one of the most rewarding fish to catch.

Table Quality

Their fatty flesh is highly prized in Japan, especially late in the season when fat content is at its peak. Whether you’re catching them for sport or the dinner table, SBT is one of the most valuable fish in the ocean.

Final Thoughts

Southern Bluefin Tuna is a legendary fish for both sport and commercial fishermen. Whether you’re trolling offshore, drift fishing in deep waters, or targeting them commercially, understanding their biology, migration, and best fishing techniques will give you the best chance at landing one of these powerful, prized fish.

So, if you’re heading out to chase big bluefin, be prepared for a battle, because these fish don’t give up easily!

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