The epibiont Xenobalanus globicipitis indicates differences in swimming kinematics among cetaceans

Abstract

Most research on cetacean swimming has been conducted on captive dolphins due to limited accessibility to wild cetaceans. Epibiotic barnacles have been used as indirect evidence of cetacean hydrodynamics, given their lifelong association with cetaceans and dependence on water flow. Previous studies suggested that the spatial distribution of the barnacle Xenobalanus globicipitis on the tail flukes of striped dolphins (i.e., higher load in the center and dorsal side) sheds light on dolphin hydrodynamics. The present study investigates whether these spatial patterns are shared among 13 cetacean species: 1 species of baleen whale (N=33), 3 beaked whales (N=11), and delphinids: 3 globicephalines (N=21) and 6 smaller dolphins (N=118). We found higher barnacle densities on the dorsal side of the flukes of delphinids, particularly in the smaller species (mostly subfamily Delphininae); whereas both fluke sides of the whales were equally colonized. The center of the flukes was generally a preferred settlement location for X. globicipitis, although it became less predictable in the ventral side of dolphins. Our findings conform to evidence on cetacean morphokinematics: while large odontocetes and whales have greater mobility in their torso during swimming, dolphins rely mostly on asymmetric fluke oscillation, likely favoring a set of more favorable conditions for barnacle settlement on the dorsal fluke side of dolphins (i.e., higher cyprid advection and lower shear stress). Also, the interaction of the dorsal fin vortices with the flow at the flukes could be more pronounced in dolphins. An additional effect of dolphin aerial behavior cannot be ruled out. This study provides novel indirect evidence on cetacean swimming performance, highlighting possible nuances between ecomorphological groups, and underlines that epibionts are a cost-effective tool for studying wild cetaceans.