Why do spinner dolphins spin?
No single factor is considered to be the reason for the aerial spinning behavior (Hester et al., 1963; Norris and Dohl, 1980; Norris et al., 1994). The various factors include leadership or dominance, alertness, acoustic communication, courtship display, defining positions of members in the school, and dislodging ectoparasites. The most notable ectoparasites are remoras and whalesuckers (order Perciformes, family Echeneidae). ... Hester et al. (1963) suggested that the aerial maneuvers executed by spinner dolphins are involved in the removal of remoras. ... While aerial spinning maneuvers may not have developed specifically to remove ectoparasites like remoras, dynamically it is plausible that this proves to be an added benefit.


--Dynamics of the aerial maneuvers of spinner dolphins