A lot of tuna are lost right at the side of the boat, not because the angler did much wrong on the fight, but because the gaff was too small, too long, too short, or simply the wrong style for the fish being targeted. If you are asking what size gaff for tuna, the real answer is not one number - it depends on the size of the tuna, your boat height, sea conditions and whether you are trying to boat the fish quickly or control it beside the hull.

For most Southern Bluefin tuna and similar offshore tuna work, a fixed or flying gaff with a hook gape around 3 to 4 inches and a handle in the 6 to 8 foot range is the practical starting point. That covers a lot of real-world fishing off South Australia. Smaller school fish can be handled with less, while bigger barrel tuna demand more steel, more reach and a lot more control.

What size gaff for tuna depends on the fish size

The biggest mistake is buying one gaff and expecting it to suit every tuna from a school fish to a proper barrel. A gaff that is perfect for a 12kg fish can be underdone on a 70kg fish, and a big heavy game gaff can be awkward and clumsy when a smaller tuna is circling fast at the boat.

If you are targeting school tuna in the roughly 8 to 20kg class, a gaff with a 2 to 3 inch hook gape is usually enough. You still want decent strength, but you do not need an oversized hook tearing a large hole in softer flesh. A handle around 5 to 6 feet often suits trailer boats where the gunwale is not too high above the water.

For the common mid-range tuna many local anglers chase offshore, roughly 20 to 50kg, a 3 to 4 inch gape is where most setups start to make sense. This gives enough bite to hold solidly in the shoulder area without becoming cumbersome. Pair that with a 6 to 8 foot handle and you have a versatile option for a lot of boats and a lot of tuna work.

Once you are talking serious barrel tuna, the question of what size gaff for tuna shifts from convenience to control. A 4 inch or larger gape, or a proper flying gaff setup, is often the safer call. These fish have weight, power and momentum, and a light, undersized gaff can turn a clean shot into a disaster very quickly.

Handle length matters as much as hook size

A lot of anglers focus on the hook gape and forget the handle. In practice, handle length changes how easy the shot is, how safe the deck work is, and how much leverage you have once the fish is stuck.

Shorter handles are easier to control. They are quicker in close, less tiring to hold out over the side, and often better on smaller boats with low sides. The trade-off is reach. If the fish is sitting wider from the hull in sloppy conditions, a short gaff can leave you lunging when you should be waiting for a better angle.

Longer handles give reach, which helps on larger boats, high-sided hulls, and fish that will not settle close. But they are heavier and harder to place cleanly, especially when the tuna is doing tight circles near the boat. Too much length can make a good gaffie miss the shot or hit in the wrong place.

As a rough guide, 5 to 6 feet suits smaller boats and school fish, 6 to 8 feet is the all-round range for many tuna anglers, and anything beyond that is usually a specialised choice for bigger boats or heavier fish.

Fixed gaff or flying gaff?

For smaller tuna, a fixed gaff is straightforward and quick. You stick the fish, lift or control it, and get it aboard. It is simple gear and for the right size fish it does the job well.

For larger tuna, especially heavy Southern Bluefin, a flying gaff makes more sense. Once the hook is set, the detachable head and rope let the fish stay connected without using the pole as a giant lever. That reduces the chance of tearing out and gives the crew more control during a chaotic moment at the side of the boat.

If your tuna fishing regularly pushes into proper heavy fish territory, this is one area where buying up makes sense. It is not about showing off with game gear - it is about landing fish cleanly and safely.

Where to gaff a tuna

The right gaff size helps, but placement matters just as much. With tuna, you generally want a solid shot in the shoulder area or head region where there is tougher structure and better holding power. Gaffing too far back into softer body tissue increases the chance of pull-out, especially on larger fish that are still green.

This is another reason not to oversize the hook unnecessarily. A massive gape on a smaller tuna can do more damage without improving control. Match the hardware to the fish and aim for one clean, committed shot rather than poking around and hoping for the best.

If the fish is intended for release, a gaff is not the right tool at all. In that case you are looking at leadering, tail ropes where legal and practical, or release methods that avoid punching steel into the fish.

Boat setup changes the right answer

The same tuna can require a different gaff setup depending on the boat. On a low-profile trailer boat, a 6 foot gaff may be ideal. On a larger hardtop or game boat with more height off the water, that same gaff can suddenly feel too short.

Sea state matters too. In calm water you can often wait for the fish to plane close and take an easy shot. In chop, timing gets harder, the fish can surge under the boat, and extra reach becomes valuable. But there is always a balance. More reach is only helpful if the person on the gaff can still control it properly.

That is why experienced crews often build their setup around the boat first, then the fish size second. It is no good choosing a textbook tuna gaff if it does not suit the way your cockpit actually works.

What size gaff for tuna on South Australian trips?

For many South Australian anglers chasing Southern Bluefin, the practical all-round option is a strong 6 to 8 foot gaff with a 3 to 4 inch gape, backed by a heavier option or flying gaff if barrel fish are likely. That covers a broad middle ground without locking you into an oversized setup for every trip.

If you mostly fish for school-sized tuna and want an easy all-rounder, stay towards the lighter end. If your trips are built around bigger fish, rougher weather windows and proper offshore work, buy for the top end of the job, not the average day. The cheap or undersized option nearly always becomes expensive when the fish of the season turns up beside the boat.

At Reel ’N’ Deal Tackle, that is the kind of gear choice worth getting right the first time - practical, species-specific and matched to how you actually fish.

Common mistakes when choosing a tuna gaff

One common mistake is buying by hook size alone. Anglers see a big gape and assume bigger must be better. In reality, balance matters. The hook, pole, grip and overall weight all need to work together.

Another is ignoring storage and deck space. A long fixed gaff is useful only if it can be stowed safely and grabbed quickly when the fish is ready. If it lives buried under gear, it will not help when the tuna pops up at the transom.

The third is forgetting the crew. If one person on board is always the gaffie, choose a setup they can handle confidently. The best gaff on paper is the wrong one if it is too heavy or awkward for the person actually using it.

The practical answer

If you want the short version, here it is. For smaller tuna, look at a 2 to 3 inch gape with a 5 to 6 foot handle. For general tuna fishing, especially 20 to 50kg fish, a 3 to 4 inch gape and 6 to 8 foot handle is the sweet spot. For big barrels, step into heavy-duty gear with at least a 4 inch gape or a proper flying gaff setup.

That gives you a starting point, not a rule carved in stone. Fish size, boat height, crew experience and conditions all matter, and they matter more on the day than any catalogue spec ever will.

If you are unsure, buy the gaff that matches the tuna you are most likely to catch, not the one fish you hope turns up once a season. Then make sure it is sharp, accessible and in the right hands when colour shows beside the boat.