you can also find a couple of suggestions in the web just search - horseriding in Mauritius. Unfortunately I din't find any prizes.
except when you dive outside the reef there is no more other place to find sharks. In the north where there was a place, they have disaappeared according to the agency that did this excursion.
Weather should be fine in May it's the end of summer.
Hope this will help you a little. Brgs Barbara