Hammer it out: shifts in habitat are associated with changes in fin and body shape in the scalloped hammerhead (Sphyrna lewini)

Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.

Automated summary

The study found that scalloped hammerhead sharks undergo significant morphological changes in response to changes in habitat, including adaptations in head morphology, fin length, and aspect ratios. Additionally, larger individuals may exhibit better locomotor efficiency.