Abstract

BackgroundGreat 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.ResultsWe 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.ConclusionWe 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.

Highlights

  • Great hammerhead sharks (Sphyrna mokarran) routinely swim on their sides and periodically roll from side to side

  • Royer et al Anim Biotelemetry (2020) 8:11 et al [5] using multi-sensor accelerometer instrument packages observed great hammerhead sharks (Sphyrna mokarran) spend up to 90% of their time swimming on their sides at a roll angle of between 50 and 75°

  • Instrument deployments and fin measurements We deployed biologging packages on 11 adult male scalloped hammerhead sharks ranging in size from 204 cm to 270 cm Total Length (TL, Table 1) of which 10 were successfully recovered and 9 recorded accelerometer data

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Summary

Introduction

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) have proportionally taller dorsal fins compared to pectoral fins than most shark species and similar to that of great hammerhead sharks, and 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. Scalloped hammerhead sharks (Sphyrna lewini) have a similar body plan to great hammerhead sharks, including a tall first dorsal fin that may be longer than their pectoral fins and in theory, could exhibit side swimming behavior to reduce their transport costs. Our objectives were to determine whether scalloped hammerhead sharks exhibit rolling behavior and if so, whether there are any patterns in that behavior and any interplay between rolling behavior and other aspects of swimming performance

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