Up for Air

Harbor Seal (Phoca vitulina)

It was an almost birdless morning. A few crows, a gull or two, one Snowy Egret, one probable cormorant in the distance. That was the visible bird population of the North Basin waters. But, as if by way of consolation prize, a Harbor Seal (Phoca vitulina) poked its head above the waves, had a look around, and grabbed some of the fresh, sunshiny air that prevailed this morning. You can tell it’s a Harbor Seal and not a Sea Lion because it ears are in holes without ear flaps; the Lions have ear flaps.

I noticed in looking at the snapshot that its eyes are opened an unequal amount. The eye that’s in the dark side of its head, away from the sun, is open wider than the other one that’s on the sunny side. You can see a similar adaptation with birds, where their pupils vary in openness between the two eyes depending on sun exposure. I don’t know if we humans can do that — do we have an ophthalmologist reader?

Note also in the video how the seal leans backward into the water when going under. That’s just the opposite of what birds do; they go forward. The seal’s move may have to do with the fact that seals breathe out and empty their lungs before diving. They use oxygen already in their blood, and they slow their heartbeat from 100 bpm to 10 bpm while underwater. With that heart rate they can swim at a steady 6 mph underwater with sprints up to 18 mph. They can dive down to 1500 feet and stay underwater for half an hour. The seal is a highly adapted mammal that operates in a whole different league from unaided human diving efforts.

Harbor Seal (Phoca vitulina)

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5 thoughts on “Up for Air

  • To Peter Rauch:
    Excellent feedback, thank you. The link you provided says that unequal pupil dilation in humans is anisocoria and may be the sign of injury, disease, or even life-threatening emergency.
    In birds, though, at least our Burrowing Owls, it seems to be routine. See e.g. https://chavezpark.org/first-owl-portraits/
    I’ve not found a source that discusses whether harbor seals or other pinnipeds have individually adaptive pupils.

  • “I don’t know if we humans can do that”

    Dunno if that was a pondering about squinting one eye, or about bilateral differences in pupil dilation, or abut both.

    People squint or close one, or the other, or both eyelids for various reasons, including to reduce glare / brightness of light impinging on the respective eye.

    On the other hand, for normal human pupils, “[d]irect and consensual responses should be identical, whichever eye is illuminated”. (https://www1.racgp.org.au/ajgp/2019/january%E2%80%93february/unequal-pupils)

  • I noticed the eye difference too and wondered if left eye was injured. I miss volunteering at The Marine Mammal Center!

  • what a perfect video! thanks

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