I have seen a couple.
First experience, barely planing about 2km off the beach heading back in, on board 10L less than my weight, gusty wind gradually dropping at the end of the day and I saw a 3m ish shark head under me (perpendicular).
I had to bear away to keep planing, wind was gusty and I did not wanna sink so I ended up losing about 500m downwind in a 2km reach

but it was worth it. Never saw him come back for a look but it was a grey day, choppy etc. I was sh!tting myself all the way back!
Second one was (for those who know it) at 9 mile in Esperance.... I was in the carpark which is about 200ft above sea level and looking down you can see everything, the water si so clear. Saw a couple of guys tearing up waves and a shark about 3m long was cruising along the beach. One guy bottom turned over the top of it in no more than 2m of water and the shark maintaiend course and speed... not even interested.
My take on it is they are not too fussed about us unless we fall in
and are thrashing about
and they are hungry
and don't see us well (like in whitewater in the waves) and they take a curious bite.