Researchers have discovered how seals and sea lions evolved to swim, findings which could have potential implications for improving the design of machines such as underwater drones and submersibles.
While biologists have long known that seals and sea lions have had two different methods for swimming, the reason behind this has been a mystery.
By using cutting-edge engineering alongside footage of animal behaviour, scientists can now explain the origins of efficient swimming in the animals.
Seals and sea lions are fast-swimming ocean predators that use their flippers to “fly” through the water.
But not all seals are the same – some use their front flippers to swim, while others propel themselves with their back feet.
Fur seals and sea lions have wing-like front flippers specialised for swimming, while grey and harbour seals have stubby, clawed paws and swim with their feet.
A new study led by Australia’s Monash University and including scientists from London’s Natural History Museum (NHM) has attempted to understand the evolution of these distinctive styles to finally answer the mystery.
“One of the key specimens used in this study was a female grey seal that was brought to the Natural History Museum after its remains were found in Margate,” said Dr Travis Park, a researcher from the Natural History Museum who was involved in the study.
“Along with help from the Royal National Orthopaedic Hospital, who CT-scanned the animal for us, our scientists were able to turn this sad loss into a new understanding of how swimming in seals has evolved.”
The adult grey seal was found dead in Walpole Bay in Margate in 2018 and was taken to the NHM for study.
As well as analysing the animal’s limbs for the study, the team looked for parasites and investigated its stomach for a study into marine life ingestion of plastics.
During the dissection, the team found a metal object in the seal’s head which they believed to be the cause of death. They reported the finding to the RSPCA.
As well as real specimens, researchers used simulations to help understand how different seals propel themselves through the water.
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Lead author Dr David Hocking, of Monash University, teamed up with engineer Dr Shibo Wang, from the university’s department of mechanical and aerospace engineering, to use simulations to show how water flows around seal flippers of different shapes.
“Our analysis showed that some Antarctic seals, like leopard seals, actually have very streamlined, wing-like forelimbs, despite being from the ‘foot-propelled’ seal family,” said Hocking.
The discovery shows how wing-like flippers can evolve in seals that already swim with their back feet, providing a pathway for the evolution of forelimb swimming in the fur seals and sea lions.
“We found that grey seals still use their paws to hold their prey when processing it, but other seals like leopard seals have forgone this ability to maximise their swimming speed and agility, being able to capture more mobile prey,” said Park.
The study is published in the journal Current Biology, and the authors say that as well as explaining the origin of seals, the research may also improve human design.
“Seals have had millions of years to perfect their swimming, and they can teach us a thing or two about underwater grace and elegance,” said Hocking.
“Learning from them may help us to improve the design of human-built machines like underwater drones and submersibles, increasing their speed, manoeuvrability or energy efficiency.’