A hot new tuna fishery is creating excitement among game fishermen on the east coast from Gisborne north. And this weekend up to 100 boats are expected to be launched from Waihau Bay, as the anglers head out in search of southern bluefin tuna which may pull the scales down to 80 kilos.

This is a relatively new fishery, although the fish have always been there, and last year at this time saw the first frenzy spread through the sport fishing fraternity as reports of the huge tuna turning up off the coast spread through social media like wildfire.

The run starts off Gisborne in early May and the first tuna are small, followed by the big fish as water temperatures drop below 16C.

The runs continue up the east coast through to August when they reach North Cape.

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It is deep water fishing, with the schools of bluefin following bait fish like sauries and mackerel from the edge of the continental shelf out to 2000 metres of water.

As the tuna work their way up the coast the closest point from which to reach the continental shelf is about 10km off Cape Runaway, which is across the bay from Waihau Bay. Some boats head out from Te Kaha and Opotiki, but they have to travel further offshore to find the tuna.

Another reason this weekend will see an influx of trailer boats from bases like Waihau Bay is the full moon yesterday; not because fish feed on that moon phase but more for the reason that the moon influences weather and the few days around the full moon usually see calm, settled weather. These are the conditions which anglers in trailer boats need to go out wide off the coast.

Huge bluefin are tough fish and anglers need heavy tackle, at least 37kg line with matching rods and reels while some will put 60kg line – the heaviest allowed under game fishing rules – on 37kg outfits.

Lures are regular marlin and tuna lures like Pakula, Zuker and Rapala trolling lures, and the fishermen will watch for activity on the ocean; like birds, dolphins and seals which also feed on the massed schools of bait fish.

The bait and the tuna can also be picked up on the electronic fish finders which all game fishing boats are equipped with, and this technology has become increasingly sophisticated in recent years.

The bluefin make fine eating, either as steaks, smoked or bottled and the fish should be correctly handled when caught to ensure the best quality flesh. The systems were developed by the Japanese commercial fishing industry for the sashimi market which demands the finest quality fresh fish.

When boated the fish is first killed by inserting a spike in the brain – called iki jime – and a Phillips screwdriver with the end ground to a fine point makes a useful tool for this.

Then the guts and gills are removed, which the Japanese do through the mouth without cutting the stomach wall as this is the most valuable part of the fish. It is then put into a slurry of salt ice and sea water which drops the temperature quickly.

Tuna are the only species of fish where the body temperature heats up when it is in stress, as in being caught on a line or in a net. The flesh will spoil if the body temperature is not quickly cooled.

Of course if a fish is to be weighed for a competition or a potential record, it must remain whole but should still be placed in an ice slurry to keep it cold.

It is unusual to find large tuna in mid-winter as most game fish are international travellers and visit our shores in summer when the warm currents sweep the coasts on both sides.

Another member of the tuna which is commonly caught off the coast at this time of year is the albacore tuna, which may grow up to 30kg and have traditionally been caught off White Island in June and July.

There are two other species of bluefin which visit out coasts – the northern and Pacific Bluefin tuna which can reach 300kg and are occasionally hooked while trolling for marlin in summer.

There is also a run of these giants off the west coast of the South Island in August and September, and this sport fishery is well established with boats heading out from Greymouth and fishing 30 or 40km offshore where the huge commercial hoki boats working.

Fresh water
Tomorrow is the last day of the season on some of the best known fisheries. In Rotorua Lakes Okataina, Rotoiti and Tarawera close to boat fishing, but some limited fishing is permitted from the shore through the closed season. The upper reaches of spawning tributries also close, and as the regulations vary from district to district it is important to check local rules.

Tip of the week

When handling large, powerful fish at the side of the boat it is important that all the crew know what they are doing as it can be dangerous. If the fish breaks away from the "wire man" who is holding the trace with gloved hands, all loose line should be hanging over the side of the boat and the drag on the reel should be reduced to allow the fish to swim away.

When the fish is gaffed, it should be hit in the head or shoulder, which makes it easier to pull on board as the crew actually employs the energy of the fish as it reacts to the gaff. A large fish hooked in the middle of the body is almost impossible to pull in sideways. More fishing action can be found at GTTackle.co.nz.

Bite times
Bite times are 1.35am and 2pm tomorrow and 2.20am and 2.45pm on Sunday.