Hi mr. X, so you can't wait to try the new gun, eh?
Mullets: I suspect they don't have the same behaviour everywhere, my impression is rather that their reaction to the presence of a spearo may change based on the experience of the local mullet population: believe it or not, fish LEARN to stay away from spearguns.
In areas with lots of active spearos, such as in my Tuscany, mullets are very shy and will swim away quickly soon as they detect you. But in other areas, where spearfishing is less popular, I found very dumb mullets who came close with no fear.
Being pointless to talk about dumb, easy fish, the shy ones must be hunted with the agguato and aspetto techniques mixed together.
Basic agguato:
You have to dive to the bottom BEFORE seeing the fish and then start to look for them: Dive very silently belly-crawling on the bottom (Old Man Dave calls this technique "indian style"), with minimal fin strokes or no fin strokes at all, using your free hand to grab to help the crawling.
Swim large silent loops around kelp bushes and rocks, stopping every little while to have a look around, and every while TURN, make a curve around the rocks and bushes trying to take by SURPRISE the eventual fish being behind the obstacle. If they're there at range, aim and shoot. If they're too far, lay very flat on the bottom, still covered behind something, and wait hoping they will come closer.
If you scare them they will disperse far away, but don't lose hope: they're curious fish, and many times they will just swim a large loop to get back to you, for investigating about you. This time they're more likely to come at range, because their initial fear of your vibrations will be methabolized and they'll feel more self assured.
Of course, waiting for them to come back might require a long breath hold. If it's too much, just surface very silently, ventilate for as long as necessary, then go back down very silently to the place you were at before. If you're lucky, the mullets are coming back to the same place. It happens sometimes.
Mullets in schools
In my waters, mullets tend to swim around in large number schools when young, and in smaller groups of 2 or 3 when adult. They rarely will be found alone.
It's very difficult to hunt fish when in schools/groups, because schools always have a sort of sentinel alarm system: if you scare one, you scare them all.
Once they get nervous, they start swimming faster and you will certainly get jammed by all those fishes dispersing around, and you will loose precious time trying to make a decision on WHICH ONE to shoot among the lot.
So the best thing, even if they are dozens, is to focus on ONE single fish, track him calmly until he comes at range, and never change target, unless your first target fish disappears.
Shooting:
If they come in schools or even small groups or pairs, NEVER target the first one of the row: if you aim to him and he detects you, he'll get nervous. And, for being the first one in front of the row, he will immediately scare all the others following from behind because they will all SEE him accelerating.
If the fish come towards you frontally, don't wait for him to turn on a side, but shoot him straight to his face. If it's close target: aim to the gill plate. Distant target: aim to his lips and one inch above his head. Try to avoid shooting the belly: the meat is very soft under there and they're likely to get broken.
...
Long post but it's just a few scattered thoughts.
I'm sure the English/Guernsey boys will give you better and more specific tips for hunting mullets in British waters.
