Hm, I found in the Internet numerous offers for daily whale and dolphin watching excursions in Tenerife. They offer watching and snorkeling for tourists. I'm okay about snorkeling just would prefer to do it with a small team of naturalists instead of crowded tourists boats.
Awesome! The visibility was not the best as I see. I was there last year the same time of year and it was similar. Planning to return there late fall or early summer/late spring for 50 meters visibility.