Hi,
Dog tooth tuna does get big, being 245cm the maximum length registered, for a weight or around 130 kilograms, still Doggies in the 80 kilo range and above are HUGE and underwater they are even bigger so its very easy to be mistaken on their size if you are not used to see and land big fish.
These monster fish have tremendous power and they usually go so fast in the first run that you have only one chance and that is to land a perfect holding or killing shot!!!
Normally two things happen:
If your shot hit the upper body from a distance and you have too much flotation (too many floats or too big floats) as soon as the fish finishes stretching the bungee he takes everything down so fast that it almost immediately rips the slip tip of he's flesh duo to the impact of the floats on the end of the line.
The second situation is to have too little flotation (not enough floats or too little floats), even if the shot is good the fish will take off to the reef walls like a rocket and simply smash himself against every coral or rock he can get a hold of, wrapping the shooting line all over the bottom and tearing it off.
Doggies normally “hang” with bad neighbors, and its not rare for sharks to tear out the fish completely, so a quick recovery, if possible is advisable.
My advice is to have good flotation for it will prevent the fish from hitting the bottom as soon as you get to the surface, but only to take the shot if it is at close range to take the spine or kill spot on the head or enough range to penetrate the gill plate or another good holding spot preventing the slip tip to be dragged out on impact of the buoys on a fast descend.
Unfortunately sometimes this fish do come bye and the gear we have in the moment simply as to do the trick…
For doggies as well as marlin I do recommend a slip-tip, its does improve your chances of landing these fish.(Rob Allen has an excellent one, the Slip-Tube, I have landed a 110 kg black marlin with it and I must say it performs very well)
As for the flasher you should have it with you on the water attached to a separate float.
Have your spearing buddy to work it as you are down and vice-versa.
Always keep it at a depth confortable to you, if its too deep there's a good chance you dont make it to the fish as well as not safe at all.
“Chumming” does work well on tuna, at least much better then flashers, but since you mention a healthy population of tiger sharks in the area, and if you don’t have much experience of spearing in “sharky” waters I really don’t recommend it.
A 140 gun, double 16mm bands, (a bit shortened to help driving the slip tip) with a 7,5mm spear, and slip tip will do the job just fine, being mobile and fast enough to cope with other smaller open water preys.
A 170 does give a good advantage in range if well rigged, but it has its limitations on manouvrebility and fast response. My biggest gun is 160, and i only use it while bluewater hunting and with excellent viz.
Best regards,
Dias