The end of the summer is approaching, but fortunately here in São Miguel it feels far away still. Dolphins and whales cheer us up whenever encountered making everyday special and bright!

This week (13-19 September 2010), we observed five different species, the bottlenose dolphins, the common dolphins, the Atlantic spotted dolphins, the pilot whales and the sperm whales. 

Both whales and dolphins are often seen breaching out of the water with spectacular jumps. The reason for these acrobatic leaps can be various from courtship display, simple fun or related to a less joyful cause like trying to eliminate parasites! Cetaceans are in fact affected by various ectoparasites which in some cases can produce damage on their skin, but do not cause death.

Below is a photo of an Atlantic spotted dolphin (Stenella frontalis) while leaping out of the water and showing a parasite attached on its flank.

 Ectoparasites of whales and dolphins include the acorn and stalked barnacles typically found on humpback whales, or the Cryptolepas rhachianecti another barnacle species found on gray whales. Barnacles are not true parasites as they don’t feed on whale skin, rather they exploit the swimming of the whales to filter food in the water. However, when in great number they can bother whale movements. Gray whales are also affected by lices gathering around wounds and scars and feeding on their skin. Other parasites damaging skin tissue are cookie cutter sharks and possibly sea lampreys.

 During one of our encounters with Atlantic spotted dolphins we had the chance to enjoy the sighting of some young individuals leaping high into the air. One of them, at closer look, showed a parasite attached on its flank. Although the resolution of the picture doesn’t help to identify the parasite, its size and shape suggests it could be a cookie cutter shark.     

 Cookie cutter sharks (Isistius brasiliensis) are so called because they leave cookie-shaped scars on the body of large fishes and marine mammals. They have a cylindrical body and a circular mouth, which contains many teeth used by the shark to remove the flesh of the host.

 When we see dolphins showing their acrobatic skills it is not necessarily due to parasites luckily for them, and many exhibitions are related to a courtship display during the breeding season.