you never get to see them. reporter: local fisherman paul fong snapped these shots of a great white off hihiboat. i seen a lot of sharks, you know, fishing and tuna fishing and doing some other things out there. but never seen a great white before. reporter: a new study shows unprovoked shark attacks are on the rise. there were 79 in 2010. up from 63 in 2009. 42% of those attacks happened in north american waters. the majority in the united states. one reason the sharks like this area, these beaches are full of seals. the seal population has grown here. you just walk around and you see so many of them. and of course, seals are a food source for sharks. swimmers are being urged to be extra vigilant when they re in the water and to visit beaches where the seals aren t around. be alert, be aware. if you see a shark, anything that might look like a shark, get out of the water and notify authorities. reporter: linsey davis, abc news, new york.