New insight into the swimming kinematics of wild Green sea turtles (Chelonia mydas)

Abstract

Biomechanically, sea turtles could be perceived as birds of the ocean as they glide and flap their forelimbs to produce the necessary forces required for locomotion, making sea turtles an interesting animal to study. However, being an endangered species makes studying the sea turtle's biomechanics a complex problem to solve, both technically and ethically, without causing disturbance. This work develops a novel, non-invasive procedure to develop full three-dimensional kinematics for wild sea turtles by filming the animals in Australia's Great Barrier Reef using underwater drones without disturbing them. We found that the wild animals had very different swimming patterns than previous studies on juveniles in captivity. Our findings show that the flipper goes through a closed-loop trajectory with extended sweeping of the flipper tip towards the centre of the carapace to create a clapping motion. We have named this the “sweep stroke” and in contrast to previously described four-stage models, it creates a five-stage cycle swimming locomotion model. The model presented here could lead to a better comprehension of the sea turtle propulsion methods and their fluid–structure interaction.

Exploring the relationship between environmental drivers and the manifestation of fibropapillomatosis in green turtles (Chelonia mydas) in eastern Brazil

“…It is noteworthy that turtles in group “posterior” presented generally higher FPI values ( Table 2 and Fig 5B ), indicating that their FP tumors were larger and/or more numerous, and this was mainly due to the FPI contribution from the hindlimbs ( Fig 5C ). Green turtles rely primarily on their forelimbs to swim, keeping their hindlimbs tucked in and pointing back to reduce drag [ 85 , 86 ]. It is plausible that the mechanical stress associated with drag poses a constraint to tumor growth rate, with tumors at anatomically sheltered sites such as the hindlimbs showing increased growth.…”

Soft-robotic green sea turtle (Chelonia mydas) developed to replace animal experimentation provides new insight into their propulsive strategies

“…However, gaining this understanding is of enormous complexity. Firstly, studying an endangered live animal brings tremendous inconvenience in obtaining ethical approvals 5 . Additionally, the animal may not even swim with its natural locomotor pattern when in captivity 5 .…”

“…Firstly, studying an endangered live animal brings tremendous inconvenience in obtaining ethical approvals 5 . Additionally, the animal may not even swim with its natural locomotor pattern when in captivity 5 . To overcome these limitations, researchers have tried to design and build animal-inspired robots to help comprehend and take advantage of unique animal characteristics 6 – 12 .…”

“…While other works have introduced three degrees of freedom 15 , 17 , 19 , 20 the main goal in their works was not to try and truly mimic the sea turtle but demonstrate a novel turtle-inspired robotic technology. In recent work, an updated sea turtle locomotor description for the animal's general swimming routine is provided by van der Geest et al 5 , which details the 3-dimensional flipper patterns, including the active twisting of the flipper. They found that wild green sea turtles had a different swimming pattern than previous studies on juveniles in capitivity 21 .…”

“…During the green sea turtles general swimming routine it is understood green sea turtles produce an average limb beat cycle of about 0.23 Hz 5 , 22 to swim an average speed of approximately 0.6 m/s 22 – 25 .

Figure 1 Five stages of the green sea turtle's swimming pattern as illustrated with coloured spheres 5 . ( a ) Swim pattern viewed from the sagittal plane ( b ) Swim pattern viewed from the Coronal plane.

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