Published On: Tue, Apr 4th, 2017

Southern Bluefin Tuna – Thunnus maccoyi – southern bluefin tuna

Southern Bluefin Tuna – Thunnus mccoyi

Murray Whyte, bluefin tuna, image.

Murray Whyte with a Southern Bluefin Tuna he caught fishing off Fiordland, New Zealand.

Southern Bluefin Tuna

The body of the southern bluefin tuna is almost round in cross section. The first dorsal fin folds down into a groove on the back affording the fish an almost perfect bullet like shape free of protrusions that would hinder forward swimming speed. There is a caudal keel stabiliser at the base of the tail. There is also small finlets present between the second dorsal fin and the tail, and also between the anal fin and the tail. The pectoral fins are relatively short for a tuna. The body is covered with small scales.

The body colour is blue to black on the back and silver to white on the flanks and underside. Fish fresh from the water are a dark metallic blue. The finlets in the upper and lower surfaces near the rear of the body are yellowish edged with black. The caudal keel is yellow on smaller fish and much darker on larger fish.

Southern bluefin tuna lineart image

Southern bluefin tuna

The southern bluefin tuna is now classified as Critically Endangered on the IUCN Red List of Threatened species. Overfishing by commercial interests has greatly reduced their numbers to the extent that they are nowhere near as abundant as they were back in the 1970s.

This species can grow to a maximum length of 2.5m and weigh over 400kg. The southern bluefin is a large, fast-swimming migratory tuna found in southern oceans between 10 degrees South and 50 degrees South during the autumn and winter. Its preferred temperature range is 10 to 22 deg C. The best New Zealand fishing grounds for bluefin tuna are off the West Coast of the South Island. During the summer months, schools are occasionally seen on the surface. These migratory schools usually contain fish of a similar size as they pursue squid, anchovies, sauries and pilchards.

A bluefin tuna caught by Steve Smith off Fiordland, in New Zealands deep south. The fish species that every sport angler would love to catch. Photo: Lex Coutts

A bluefin tuna caught by Steve Smith off Fiordland, in New Zealand’s deep south. This is the fish species that every offshore angler would love to catch. Photo: Lex Coutts. Click on image to enlarge.

Like other migratory tunas, the southern bluefin is able to maintain a body temperature up to 10 degrees C higher than the surrounding water temperature making it possible for them to make sudden extremely quick bursts of speed in pursuit of prey.

Big southern bluefin tuna have been taken off the West Coast of New Zealand’s South Island while drift fishing fillet baits in a burley trail. This method has proven successfully in as bluefin follow hoki trawl nets to the surface.

Fishing Methods

Bluefin tuna are taken by anglers trolling Hexheads, Konaheads and Rapalas in offshore waters out from Westport and Greymouth. Strikes are more likely on tuna when lures are trolled on monofilament leaders instead of wire.

It also pays to keep the boat moving forward when a lure is struck as this often results in multiple strikes on other lures at the same time.

In general deep water ocean trolling for bluefin tuna is a somewhat “hit and miss” affair. The waters off the South Island’s West Coast are often rough, and there is almost always a considerable swell running. Look for surface activity signalled by the presence of mollymawk and shearwaters.  Expect bluefin to make a powerful surface run when first hooked that may take out several hundred meters of line. As the fish begins to tire it will most likely go deep and slug it out well beneath the boat circling in an anti-clockwise direction. On lighter lines, this battle can easily drag on for many hours.

The flesh of the southern bluefin tuna is excellent eating and is much prized in Japan particularly fish caught late in the season when the flesh has its highest fat content.

Southern Bluefin Tuna – Thunnus mccoyi – with Gary Wilson

Description

Exquisitely coloured blue-black above with silvery white belly. First dorsal fin grey with a yellowish tinge, with 2nd dorsal a reddy brown and anal fin silver. All other finlets are bright yellow with tinges of black. By Far and away the largest of the tuna species present in South Island waters. The average size for this tuna species is 40cm to 1.5m and average weight 20 – 50kg although large specimens can reach lengths of over 2 meters and top a massive 180kg in weight.

General

The southern bluefin is a very large and powerful migratory tuna capable of swimming vast distances during the course of a year. This species has a broad distribution in the southern hemisphere and can be found in waters off the coasts of Australia, South Africa and New Zealand although – like most of our tuna its migration patterns and growth rates are poorly understood. We know that the stocks present in New Zealand waters breed in the waters south of Java in the Indian ocean and the juveniles migrate along the west and southern coasts of Australia and then on around Tasmania and into the Tasman sea. By the time they arrive on New Zealand’s shores they have reached adulthood. Along the way, they have also been susceptible to heavy commercial pressure from both Japanese and Australian sources.

From here it is believed that the bluefin retraces their steps again making their way back to the tropics to breed.

Here in New Zealand, the bluefin is relativity common in South Island waters with it being present off both coasts for at least several months of the year. Prime time to locate these tuna in West Coast waters is between the months of February and May. Whilst anglers searching for the less available East Coast stocks have to target the brief period between April and July, this is when a small run of fish make their way up the East Coast to around Kaikoura. This run appears to be fairly small and each year only a few fish are extracted from it. 

One year on the East Coast just four fish were taken – all of which were caught commercially. Testimony to the existence of this run is the mounted bluefin on the wall of the Cheviot garage. This fish was taken, as most are, on a long line, quite some years ago.Chasing bluefin in the south of the country is an altogether different proposition. Here greater numbers of fish over the last few seasons has allowed the recreational angler the chance to tangle with one of these exquisite gamefish with a more than reasonable chance of success. ln fact over the last couple of years the norm has been for the average days fishing to produce not one but several shots of landing a fish and a good day could quite easily see 2 or 3 fish boated, which by anyone’s standards has to be great fishing, especially considering that only a short few years ago these fish were nearly non-existent off our coasts.

Chasing bluefin in the south of the country is an altogether different proposition. Here greater numbers of fish over the last few seasons has allowed the recreational angler the chance to tangle with one of these exquisite gamefish with a more than reasonable chance of success. ln fact over the last couple of years the norm has been for the average days fishing to produce not one but several shots of landing a fish and a good day could quite easily see 2 or 3 fish boated, which by anyone’s standards has to be great fishing, especially considering that only a short few years ago these fish were nearly non-existent off our coasts.

The primary area for targeting bluefin in the deep south is in the wild and rugged waters off the Fiordland coast here the angler has the choice of chartering one of the local operators, or if they are really keen, trailering their own rig into either Milford or Doubtful Sounds, and motoring the 20 or so km out to the heads each morning before setting their gear. The drawback with the latter system is two-fold.

First, the weather which traditionally is extremely wet and wild and can lay the angler up in port for days at a time. The second problem is the need to be almost totally self-sufficient in every area. Food, fuel and tackle are not readily available so virtually everything required for the trip has to be brought in with you. It can be quite a logistical challenge getting fuel for a week’s fishing into such a remote area but the results are defiantly worth while. To tangle with one of these massive fish with our own gear has to be one of the ultimates in South Island angling.

Tackle for Southern Bluefin Tuna

Soft plastic squid lure bodies are ideal for bluefin tuna. They run straight causing fewer problems than bibbed minnows. A lumo stick can also be placed inside the squid body.

Soft plastic squid lure bodies are ideal for bluefin tuna. They run straight causing fewer problems than bibbed minnows. A lumo stick can also be placed inside the squid body.

Here as in other parts of the world the primary method for the capture of these fish is by trolling. Although at times they will respond to both live baiting and chumming, most of the angling for bluefin in Fiordland is done by dragging hex heads, soft-bodied squid lures, Rapalas and other small to medium sized trolling lures around, out in the open ocean outside the mouths of the sounds.

Lures with proven track records are CD 18s – blue and silver and mackerel colours, Yo-Zuri soft-bodied squids – brown and natural. As well as Pukula Pushers in a large selection of colours. These are usually mated to a strong reliable rod and reel combos with Shimano and Penn being the front runners here and the reels are generally spooled to capacity with line classes in the heavier end of the range with 15, 24 and 37kg being the most popular.

The fight of a bluefin, like all tunas, is characterised by long hard scorching surface runs and plenty of deep, tough, and draining circling, and is guaranteed to keep the angler busy for at least an hour or more. Just a word of warning here a good reliable drag is a must when tangling with these fish but the angler must be careful not to apply to much pressure as most tuna have fairly soft mouths and too much pressure applied throughout a prolonged fight could quite simply rip the hooks out resulting in the loss of a good fish. So as a rule of thumb go a little easier on the drag when fishing the heavier line classes.

The eating qualities of bluefin tuna are well known. These are the fish that the Japanese pay megabucks for in the Asian fish markets and that is the primary reason that they were nearly fished into extinction in local waters a few years ago. Thankfully the last few years have seen an increase in their numbers off our coasts due mainly to a decrease in international fishing pressure but this recovery is again under threat as the Japanese again threaten to destroy the bluefin’s fragile come back by exceeding the international quotas specifically laid down to allow the bluefin breeding stocks to recover by again sending up to an extra 50 boats into southern waters some years to yet again over fish this species. Hopefully, international pressure and common sense will prevent this from happening before the mighty bluefin tuna is once again fished to the brink of extinction.

About the Author

Profile photo of Allan Burgess

- Fishingmag.co.nz website editor.

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