Cleaning interactions by bluestreak cleaner wrasse (Labroides dimidiatus) and moon wrasse (Thalassoma lunare) on pelagic thesher sharks (Alopias pelagicus)

Abstract: Cleaning symbioses are a well-studied mutualism among marine species. However, the interactions occurring between cleaner fish and sharks are lacking in research, which makes it a target for further investigation. With this study, intentions were to analyse the behaviour of two kinds of cleaner species, bluestreak cleaner wrasse (Labroides dimidiatus) and moon wrasse (Thalassoma lunare), to be able to distinguish differences in cleaning behaviour on pelagic thresher sharks (Alopias pelagicus). A total of 68,4 hours of video was recorded on the edge of a seamount outside of Malapascua, called Monad Shoal, during 18 days in January 2018. The number of interactions were divided into two categories, where the behaviour was classified as an inspection or a bite and could occur on different patches of the sharks’ body (head, gills, body, dorsal, pectoral, pelvic or caudal fin). In total 118 events occurred which comprised in total 4079 interactions from the two cleaner species. Of these interactions 3626 were considered inspections and 453 were bites. Bluestreak cleaner wrasse conducted 3598 of the inspections and 28 of the inspections were conducted by the moon wrasse. All bites were conducted by bluestreak cleaner wrasses. The results indicated a preference in patches of the body to inspect, where the pelvis got the most inspections on 34,1 %, followed by the pectoral fins on 22,8 %. The dorsal fin and the gills accounted for the least number of bites, with 1,3 % on the dorsal and 1,4 % on the gills. Furthermore, a difference in inspected patches between males and females were discovered, where females got significantly more inspections on their head, gills, body, dorsal and pectoral fin. The pelvis and caudal fin did not show any significant differences.