When I dive into the water, I sometimes get water up my nose and rushing into my ears. My ears sometimes crackle and my sinuses feel like they’re going to pop. That’s when I wish I were a seal or a dolphin that can whoosh into the water effortlessly with a streamlined entry. I love watching a seal glide off the rocks, swim out, arch its back and disappear into the deep. We are mammals too, so why is it so much easier for marine mammals to dive than humans?

As far as mammals go, there aren’t very many that can dive — seals, dolphins, and whales are the common ones. Several of the characteristics that make us mammals also make it very difficult to dive. When I was working on a whale watch boat as a naturalist, we used the acronym “WHALE” to remind people what defines a mammal — W (warm blooded) H (has hair) A (air breathers) L (live birth) E (eats milk). The parts of this that make diving particularly challenging for mammals are the “A” and the “W”.

Breathing air is a problem when diving because it works against you by making you float up rather than sink down. If you have air in your lungs, it is harder to dive down deep. That’s why SCUBA divers use weights to help them sink. The other problem with the air in your lungs is that it gets squished by the weight of the water as you go deeper. Your lungs can get squished right along with the air inside them, which gets squished right out into your bloodstream. The nitrogen in that air can become toxic at high levels in the blood, causing “nitrogen narcosis” or “the bends”. The air in SCUBA tanks has less nitrogen than the air we breathe in order to help out with this. That’s another issue — we can only hold our breath for so long — somewhere around five minutes is the human record.

Marine mammals have a couple of natural adaptations that help with these “A” problems. First, they can really exhale — nearly all the air in their lungs in one blow versus our measly 10% at best. That helps them sink rather than float. Also, their blood can store Oxygen much more efficiently than human blood, and they slow down their metabolism to use it up more slowly too. This allows some marine mammals like a sperm whale to stay under water for an hour and a half without coming up for air! The lungs of marine mammals are also super flexible — much more like a balloon than ours so that they can inflate and deflate with no problem under pressure. In addition, they don’t feel pressure changes in their noses and ears either the way that humans do because many do not have external ears and sinuses (hence no water up the nose or in the ears).

On to the “W” problem — the ocean temperature right now is somewhere in the 70s at the surface, which feels balmy for Maine. Nonetheless, it doesn’t take too long before we humans start to feel chilly. Water takes heat away from our bodies 20 times more quickly than air. We often put on a wet suit to provide a little insulation, and to mimic the natural insulation that marine mammals have. Their blubber, or fat layer, is better than any wetsuit people have manufactured. The shape of the human body doesn’t help either. Think about your body parts

that get cold first — your hands and your feet. They’re at the end of these long appendages called arms and legs — appendages that marine mammals don’t have. Their “hands” and “feet” are small and tucked right up against their bodies. That means that all that blood isn’t circulating along all those surfaces that are in contact with the cold water. One more component of the “W” problem is related to “H”. While marine mammals may not look hairy, many of them are — their hair is just super short and dense.

So, while I like to sometimes think of myself as part seal in the summer, hungering to spend as much time in the water as possible, it is humbling to learn more about these marine mammals that are so closely related to us but so perfectly adapted to live in a whole other world that we are only able to visit for as long as a breath with allow.

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