IT's actually an interesting point I never considered. If they truly were throwing sheep overboard, which is something they need to prove in order for this point to be credible, it definatly could be connected to an increase in larger shark activity/attacks.
edit: also people don't take into consideration that the more commercial fishing is allowed the less fish in the sea - the more encouragement sharks are given to spread further to look for food.
Pretty simple- they're getting hungrier.
People are starting to realize now that over-fishing in the past and present could be the reason sharks are venturing closer to shore and paying more attention to human limbs.
I think it's a very valid reason for why we are now seeing more shark attacks. It's simple really, take away someones food and they get angry and hungry.