There are no sharks in Denia or any part of Costa Blanca. There is precious little of anything in terms of fish life although there is a marine reserve which start just past Javea Port but I'm not sure if it extends all the way round to Denia. Vizibility is usually good at this time of year but I'm afraid the commercial fishermen have all but destroyed inshore fisheries! The only sharks you might find are in the deep trench which if you swim for about 8 hours straight out towards Ibiza from Denia you will find!
Remember that you cannot spear in the marine reserves and the local authorities will come down hard on you if you do! Good luck.
