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

Abstract

Background: Great hammerhead sharks (Sphyrna mokarran) routinely swim on their sides and periodically roll from side to side. A previous study used wind tunnel tests with a rigid model hammerhead shark to demonstrate that the rolling behavior could improve swimming efficiency using the tall first dorsal fin as a lift-generating surface. Scalloped hammerhead sharks (Sphyrna lewini) also have proportionally taller dorsal fins compared to pectoral fins than most shark species and similar to that of great hammerhead sharks, and thus might exhibit similar rolling behavior. This was assessed by deploying multi-sensor accelerometer instrument packages on free-swimming adult scalloped hammerhead sharks to directly measure swimming depth, body orientation and swimming performance. Specific objectives were to (1) determine whether scalloped hammerhead sharks exhibit side swimming and rolling behavior, (2) characterize the patterns of these behaviors, and (3) evaluate the purpose of these behaviors. Results: We obtained 196.7 total days (4720 h) of data from 9 free-swimming adult scalloped hammerhead sharks equipped with multi-instrument biologgers with deployment durations ranging from 7 to 29 days. All sharks exhibited rolling behavior throughout the entire period of observation. The roll angle magnitude and periodicity of rolling showed a clear diel pattern. During daytime, the sharks spent an average of 48% of the time swimming at a roll angle > 30°, with an average roll angle of 41° and rolling periodicity of around 4 min. At night, the sharks spent an average 82% of their time at an angle > 30°, with an average roll angle of 60° and rolling periodicity of around 13 min. In addition to an increase in degree of roll and roll duration, overall dynamic body acceleration (ODBA) also increased at night, and tailbeat frequency was more regular and consistent than during daytime. Conclusion: We observed rolling behavior in scalloped hammerhead sharks similar to that observed in great hammerhead sharks. The diel changes in roll angle and periodicity were accompanied by other changes in swimming behavior. These changes are possibly due to interplay between reducing cost of transport and social interactions with conspecifics.

Diverse Activity Rhythms in Sharks (Elasmobranchii)

“…Qualitative studies have shown that many ram ventilating species of sharks appear to swim constantly (reviewed by Kelly et al, 2019), and acoustic and telemetric tracking studies have yielded powerful data on the movements and behavior on many of these species (Holland et al, 1993(Holland et al, , 1999Nelson et al, 1997;Weng et al, 2007;Papastamatiou et al, 2010;White et al, 2019). In recent years, advances in biologging techniques, such as the combining of accelerometry data with positioning technology, have facilitated further insight into the daily activity and behavior of elasmobranchs (Whitney et al, 2007(Whitney et al, , 2010Gleiss et al, 2009Gleiss et al, , 2013Shipley et al, 2018;Papastamatiou et al, 2018;Royer et al, 2020).…”

Diel Vertical Habitat Use Observations of a Scalloped Hammerhead and a Bigeye Thresher in the Northern Gulf of Mexico

“…Similar behavior was observed for this species satellite tagged in the tropical eastern Pacific, where scalloped hammerheads spent most of the time near surface waters, specifically above 100 m [31]. However, it is important to note that Bessudo et al (2011) [31] and Hoffmayer et al (2013) [33] found scalloped hammerheads are able to make extensive dives reaching depths of approximately 1000 m, where temperatures can reach 4 • C. Most recently, Anderson et al (2022) [47] noted a new diving record for the species in coastal-pelagic waters of Hawai'i where a scalloped hammerhead reached a depth of 1240 m. Previous research has described ways in which scalloped hammerheads increase physiological efficiency by demonstrating a "breath holding" technique that allows them to compensate and maintain a warm body while they actively pursue prey in deeper, colder depths, and by swimming on their sides to possibly help reduce the cost of transport [48,49]. However, the scalloped hammerhead described here did not seem to reach depths or temperatures that required either of these strategies.…”

PILOT tags, new non-invasive towed tags for free ranging deep-diving megafauna, advantages and challenges

“…Tags were deployed by free divers using non-invasive attachment methods (16). One 230 cm (TL) tiger shark (Galeocerdo cuvier) captured in Kaneohe bay (Hawaii) was restrained and doubletagged with both a harness-towed i-Pilot tag and a high frequency triaxial accelerometer tag attached directly to the pectoral fin (10). In addition, five sicklefin devil rays (250.5-300 cm-DW) and five blue sharks (250-300 cm-TL) were harnesstagged with G-Pilot tag in the Azores to evaluate Fastloc performance.…”