Regional variation in undulatory kinematics of two hammerhead species: the bonnethead (Sphyrna tiburo) and the scalloped hammerhead (Sphyrna lewini)

Abstract

Hammerhead sharks (Sphyrnidae) exhibit a large amount of morphological variation within the family, making them the focus of many studies. The size of the laterally expanded head, or cephalofoil, is inversely correlated with pectoral fin area. The inverse relationship between cephalofoil and pectoral fin size in this family suggests that they might serve a complementary role in lift generation. The cephalofoil is also hypothesized to increase olfaction, electroreception and vision; however, little is known about how morphological variation impacts post-cranial swimming kinematics. Previous studies demonstrate that the bonnethead and scalloped hammerhead have significantly different yaw amplitude, and we hypothesized that these species utilize varied frequency and amplitude of undulation along the body. We analyzed video of free-swimming sharks to examine kinematics and 2D morphological variables of the bonnethead and scalloped hammerhead. We also examined the second moment of area along the length of the body and over a size range of animals to determine whether there were shape differences along the body of these species and whether those changed over ontogeny. We found that both species swim with the same standardized velocity and Strouhal number, but there was no correlation between two-dimensional morphology and swimming kinematics. However, the bonnethead has a dorso-ventrally compressed anterior trunk and undulates with greater amplitude, whereas the scalloped hammerhead has a laterally compressed anterior trunk and undulates with lower amplitude. We propose that differences in cross-sectional trunk morphology account for interspecific differences in undulatory amplitude. We also found that for both species, undulatory frequency is significantly greater in the anterior body compared with all other body regions. We hypothesize that the bonnethead and scalloped hammerhead swim with a double oscillation system.

Three-dimensional movements of the pectoral fin during yaw turns in the Pacific spiny dogfish,Squalus suckleyi

“…The 3D kinematics of maneuvering behaviors are especially understudied, likely due to problems with calibrating large volumes. Volitional swimming and maneuvering has been studied in a number of large aquatic vertebrates, but is limited by the use of two-dimensional (2D) video, which may oversimplify or disregard movements not visible in the filming plane (Lowe, 1996; Blake et al, 1995; Fish, 1997; Fish and Shannahan, 2000; Rohr and Fish, 2002; Kajiura et al, 2003; Domenici et al, 2004; Porter et al, 2009; Porter et al, 2011; Seamone et al, 2014; Hoffmann et al, 2017). Recent studies have successfully demonstrated the use of multi-camera systems calibrated for 3D analysis in large volume environments (Ros et al, 2011; Sellers and Hirasaki, 2014; Jackson et al, 2016; Fish et al, 2018).…”

“…The volitional swimming behavior of sharks has been documented in a few species but is limited by use of 2D video (Lowe, 1996; Kajiura et al, 2003; Domenici et al, 2004; Porter et al, 2009; Porter et al, 2011; Hoffmann et al, 2017). Studies examining yaw maneuvering in sharks used dorsal video and focused on whole body kinematics, but asynchronous pectoral fin movement has also been noted during turning (Kajiura et al, 2003; Domenici et al, 2004).…”

Scalloped hammerhead sharks swim on their side with diel shifts in roll magnitude and periodicity

“…HH11 transitions from day to night rolling behavior as light level decreases during sunset from 19:20 to 20:00, with an increase in the roll angle and roll period swimming. Both species are noted for their maneuverability, making rapid tight turns when chasing and subduing prey [18,[28][29][30][31]. In their upright posture, they can maximize their maneuverability potential, conducting rapid tight turns while keeping their body level, due to their lateral flexure, head shape, anhedral pectoral fin positioning, and large dorsal fin [2,18,28] (Fig.…”

Volitional Swimming Kinematics of Blacktip Sharks, Carcharhinus limbatus, in the Wild

“…This is known as a double oscillating system, where the undulatory wave in the anterior body differs from the posterior body, and has been identified in sturgeon, eels, and lamprey [1][2][3]. In two hammerhead species, recent work showed a double oscillating system where wave frequency was greater, and amplitude was smaller in the anterior body compared to the posterior body [9]. Swimming kinematics can vary by habitat and experimental conditions; for example, sharks swimming in a flume expended more energy, and tailbeat amplitude decreased relative to speed, when compared to sharks swimming in a semi-natural pond [10].…”

“…We used aerial drones to capture footage from adult blacktip sharks (C. limbatus) in the wild and analyze volitional swimming kinematics using a workflow previously described for animals in a captive study [9]. We aim to quantify volitional swimming speed in relation to tailbeat frequency, tail peak-peak amplitude, and body curvature.…”