Diving with Seals

How hydrodynamic are you?

Seal swimming

As scuba divers, freedivers and snorkelers, we depend on a lot of equipment to help us get around in the water. Without the equipment, we can still move but not as efficiently. Let’s take a closer look at how our beautiful Fur seals travel.

Believe it or not, seals are not fish!  Even though a great part of their life is spent in the sea, seals are warm-blooded air-breathing mammals known as marine mammals.

When we swim we position ourselves in the most streamlined position usually with our arms out in front of us and legs trailing behind, seals bodies are naturally adapted to this same torpedo shape. Their head and the lower half is quite small compared to their midsection. So as they swim, you can see their widest part in the middle of their body and unless turning nothing sticks out further than this.

While in the water the fur seal moves its head from side to side in search of food. Its rear end acts as a rudder. The front flippers are used as oars which makes the animal ‘fly’ along under water. They are using their front flippers to swim and back flippers for steering. Their thick no-neck physiques and loosely interlocked vertebrae make them strong and flexible enough to quickly change direction and navigate difficult shores.

Seals have very sensitive whiskers called Vibrissae. Studies have been done to analyse the hydrodynamic perception in seals from there vibrissae. A variety of seal species were studied to determine their ability to recognise local water movements and follow hydrodynamic trails from objects that have passed by earlier in time. The shape of their vibrissae helps to suppress the ‘noise’ made by the seal itself while swimming while still picking up trails around itself. The vibrations of seal whiskers provide the ability to track wakes.

This ability to control the flow of water around their bodies and supress the noise surrounding their movement as well as the design of the body, which minimizes drag and the morphology of the appendages provides hydrodynamic advantages with respect to drag, lift, thrust, and stall.

Seals together with the walrus, belong to the group of animals called pinnipeds. The word ‘pinniped’ actually means ‘fin foot’. These fin feet are perfect for both swimming and walking/running.

Whilst Seals spend most of their time in the water they also ‘haul out’ onto land at certain times including lounging, sleeping, bellowing, birthing and barking. In order to support the movement of their strong flippers across the ground Fur Seals have big broad shoulders. With their ‘furry’ heads this makes them look every bit as big as they are.

Fur seals have the appearance of walking on all fours as their hind flippers move forward under their bodies and their front flippers support their weight. They also experience large oscillations in their centre of gravity to enable their limbs to be lifted and moved during locomotion.

While sea lions tend to move each hind limb independently, fur Seals are more often seen moving their hind limbs in unison for a power and acceleration on land.

It’s been said that some seals can reach approximately 20km/hr on land… Can you outrun a seal?