Diving with Seals / Marine Life

Humans and Fur Seals

Humans and Fur Seals, how alike are we?

Seals

Taking a look at the animal kingdom and more specifically mammals within the animal kingdom, we can split it into three directions.

  1. Placental Mammals
  2. Marsupials
  3. Monotremes

Seals are Placental Mammals, meaning that the baby receives its nutrients to grow directly from its mother through blood. Placental babies are born much more developed then Marsupials (pouch young) and Monotremes (egged young). Milk is provided to their young through teats. If this is sounding familiar, it should be, because we are also placental mammals. In fact, we have more in common with our fur seals than you may think.

Not only do we share reproductive traits, but we also share structural and behavioural traits. Fur seals have a similar bone structure in their fore- flippers to what humans do in their hands except seals are adapted to swimming. While seals are known for their swimming ability, they are surprisingly fast on land and could almost outrun a human. To make this possible, fur seals have an extremely flexible spine, which enables them to tuck their hind flippers underneath them, while their powerful forelimbs can hold their entire body mass off the ground. Like dogs, the fur seal can use individually or combined actions involving fore and hind flippers which gives them the ability to walk, gallop and climb. This is why you see them sitting high on rocky crevices. In the water, this large, bulky animal is something different, streamlined, graceful and agile. Their body shape while in the water becomes hydrodynamic by forming a spindle shape with the widest part in the centre. Fur seals have narrow fore- fins which allows for fast turns and less drag when manoeuvring. They have adapted well to be good at their craft.

Another feature that we have in common with the Fur seals, is that they breathe air and their ability to hold our breath. The physiological response from the human body is very similar to what occurs in within the Fur seal. The heart rate slows (bradycardia) and peripheral vasoconstriction (movement of blood to vital organs) occur to help maintain oxygen levels vital for a successful dive. This physiological response can be titled the dive reflex or mammalian dive reflex (MDR). The reason that Fur seals can still outdo us in the water is that they have the ability to control their dive reflex, but also their increase in haemoglobin, storage of oxygen, large spleen and acid buffering capacity.

Just like us, seals use thermoregulation to moderate body temperature. While we sweat and warm blood rushes to our face to cool down, seals use a similar method but utilising their flippers. Blood vessels travel through the relatively thin and furless flipper, so it can be quickly cooled along with the blood flowing through it, this is one of the many reasons you see seals with their flippers raised into the air or lowered into the water. You may think flippers are completely different humans hands, well externally, they look quite different because flippers have webbing. Internally, the bone structure is surprisingly similar – the fore flippers are very similar in structure to human hands, and the hind flippers are similar in structure to human feet.

Let’s get diving and see how our similarities compare in the water together. 

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