This article is about newborn and juvenile epaulette sharks and how they move underwater. While, of course, epaulette sharks are able to swim, they can also perform a walking movement underwater. Researchers wanted to find out how epaulette shark movement may be affected by how old they are, or if there are different factors that affect how they are able to move.
Data Collected: Age, Mass, Length, Movement
Six newborn and six juveniles, or younger, epaulette sharks were taken from Sea World, Gold Coast, as eggs and held in individual glass aquariums at the Marine and Aquaculture Research Facilities in Queensland, Australia. During the first month, the newborns fed on their yolk sacs while the juveniles got fed small fish like sardines, or white meat, and squid mantle. The goal was to use the mass and length of these individuals to see if mass and length influences movement. The widest part of the abdomen was meant to represent a cylinder to calculate how much their body shape would resist bending or flexing; animal length and mass were then used to calculate how their body shapes impact their ability to move freely.
Photo A shows a view from the top of a newborn shark, which has a much more round middle section than the juvenile shark in Photo B.
Different Strides Of The Epaulette Shark
Three different strides have been identified for this species.
- Fastest: swimming with fins not touching the ocean floor
- Slowest: walking motion with fins
- Mix: mix of walking & swimming
The fastest stride occurs when the shark is swimming and their fins do not touch the ocean floor. The slowest stride occurs when they perform a walking motion with their fins, but do not touch the floor very often while moving. This means they don’t take as many “steps,” which makes it take longer for them to move. Then there is the stride that is a mix of walking and swimming; in this stride, they begin to swim but still place their fins against the ocean floor while moving.
All three of these stride types were found in both the newborn and juvenile populations. Observations of these strides were recorded on GoPro cameras located 15 cm below the tank to provide a view from below.
Researchers used the 13 points in the photo above to calculate information about how the sharks moved when swimming or walking. They were able to track the shark’s movement using a computer software. See the results they found below!
Results Of Study
Body Shape
Body shape refers to the length and width of the shark, as well as the circumference of the shark, which is a measurement around the shark’s body.
Newborns were 20% shorter and 47% lighter than the juveniles in this study. This did not affect body width or resistance to bending between the two groups. The resistance to movement, however, was found to be three times lower in newborns than in juvenile sharks, indicating that it is easier for newborns to move in any given direction.
Velocity
Velocity, in general, just refers to the shark’s speed while moving.
Velocity was significantly different between the newborns and juveniles, and this was mainly attributed to stride, as it was the only factor that seemed to change their speed. Their speed was highest when swimming and slowest while walking. Velocity only changed due to the different stride styles, but was unaffected by an individual’s life stage (newborn or juvenile).
Tailbeat frequency and amplitude
Amplitude refers to how far the tail moves side to side during motion, and frequency refers to how often this movement occurs in a given period of time.
Amplitude trends increased among the different strides and were greatest during swimming; this makes sense because they must move their tail further to generate more force and move faster. The frequency, however, was unaffected by life stage, body width and length proportion, or movement style.
Axial bending
Given position on the body (anterior, posterior, or tail) was the only thing significantly affecting how the fins bend towards the body while moving. It was found that axial bending increases from the anterior trunk to the tail; additionally, the tail angle is almost three times greater than the anterior bending angle, meaning the tail moves further than the fins do during movement.
Duty factor
Duty factor is the amount of time the fins made contact with the ocean floor. This varied significantly, and was mainly attributed to stride type. However, it was similar between newborns and juveniles. Generally, fins contacted the ocean floor for 5% longer during slow-to-medium walking than in fast walking and pelvic fins touched the floor 5% longer than pectoral fins; this can be compared to the difference between walking and running in humans. Swimming strides were not considered for this area of the study since neither set of fins come into contact with the ocean floor.
Fin rotation
There was found to be much more fin protraction, or extension, in the slow-to-medium walking than in swimming, while fast walking was found to have an average amount of fin protraction.
An interesting finding was that fin retraction was much higher in newborns than in juveniles; this could indicate that they have to move more often to get the same outcome. Additionally, fin retraction occurred four times as often in pelvic fins compared to pectoral fins.
Why Does This Matter?
Many people have a deep love for the ocean and all of the animals that inhabit it. It is known that epaulette sharks have adaptations allowing them to still move efficiently even when exposed to environmental stressors, like varying temperature or oxygen levels.
With global temperatures on the rise, ocean temperatures have also been increasing; warmer ocean temperatures cause sharks to have higher energy demands, leading to them needing more food to maintain their activity. Warming oceans can also cause changes to the reef ecosystem, where they feed, and food availability for these sharks.
Understanding how and why these sharks are able to move so efficiently will create a path for further studies like this in the future; many factors impacting movement of carpet sharks, like the epaulette shark, have yet to be studied, thus it is important to learn as much about them as possible.
Article written by: Greer Jessie, BS Undergraduate Student, University of Florida and Shark Angels Intern.
Scientific Study: Aquatic Walking and Swimming Kinematics of Neonate and Juvenile Epaulette Sharks by Porter et al., 2022. This study was performed and written by Marianne E Porter, Andrea V Hernandez, Connor R Gervais, and Jodie L Rummer. It was published on July 27, 2022.
Photos provided by: Kat Zhou, Triton Bay, Indonesia.