Helping out a fellow surfie
Hi Josh,
I surf a bit, lot better at freediving though, mostly in NSW, water is not as warm down here.
Part of what Mako said is true, to really stay under for a long time you want to relax and do some deep breathing for at least a minute or so. This is what most freedivers do before a static breath hold or any dive. Pretty much float motionless and concentrate on relaxing and breathing & take as big a breath as you can on the last one.
I don't think you will get this chance when you get caned by a huge wave ?!
Having said this I still think it's a good idea if you learn to hold your breath longer. If you can do 3 or 4 minutes in the pool when relaxed with proper breathing, hopefully you should be able to do at least a minute or so with only one a quick gulp of air before you get held down by a big wave.
The basics are, 1st get a buddy to spot you at the Pool. Practise Slow, Deep breathing for a minute or two, then exhale a lot on the last breath, then inhale as much air as you can.
Once under water you have to try and relax as much as you can, try closing your eyes, or focusing on something like a tile in the pool. Some people meditate, almost sleep, or just kind of "space out". This is the hard part, relaxing under water, your body and mind will get better at this with practise.
Use a stop watch, and don't push yourself too much.
Do a couple of these in a row, have at least 3-5 minutes rest in between for your body to recover the oxygen. You will find that on your 3rd or 4th attempt it will be a lot easier to stay under for longer.
I got to around 3 minutes within the first month I practised this, everyone is different though.
It's learning the "relaxed state" under water that will help you with surfing, if you get held down by a wave, either go limp, or curl into a ball, but then go into the relaxed state that you have learned in the pool. It's not as easy as it sounds, the more you panic (Big Wave dumps you and you are in the washing machine), the faster your heart beats, and the faster you use up oxygen....
It would be good for you to practise to swim underwater, probably without fins too, as you won't have these when you surf. Same as above, relax & breath for a minute or so, then swim breastroke underwater. Long slow strokes with the arms, and only a light kick with the leg works well for me. I can only swim about a pool lap(50m) without fins though. (Can do 90m with my freediving fins)
Hope that might help you get started. There is heaps of info on this site about training, Bit hard to sumarise it so you will just have to search through it yourself!