Dorsal Fin Edge Proportions and Their Relationship to Swimming Strategy in Sharks

Benjamin Ronald Janitz, Ashley Stoehr

Dorsal fins play a critical role in elasmobranch locomotion by providing stability, reducing roll, and enhancing swimming efficiency. Variation in dorsal fin geometry may therefore reflect ecological niche and swimming strategy. This study quantitatively compares dorsal fin leading-to-lagging edge ratios in three shark species with differing ecological roles: the spiny dogfish (Squalus acanthias), salmon shark (Lamna ditropis), and longfin mako (Isurus paucus). Using lateral-view photographs, dorsal fin leading and trailing edges were measured and expressed as proportional ratios to account for differences in overall body size. Results revealed substantial interspecific variation: the spiny dogfish exhibited the most significant leading-edge proportion (137.5%), the salmon shark showed an intermediate ratio (116.67%), and the longfin mako displayed a symmetrical fin geometry (100%). These differences closely correspond to each species’ swimming behavior and habitat use. The elongated leading edge of the spiny dogfish enhances maneuverability at low speeds, the salmon shark’s moderately extended leading edge supports high-speed pursuit and stabilization, and the longfin mako’s symmetrical fin promotes efficient cruising during long-distance migration. These findings demonstrate that dorsal fin morphology is an adaptive trait shaped by hydrodynamic and ecological demands, highlighting the functional relationship between fin geometry and swimming performance in sharks.