Cold Water Survival, Mammal Style

Spent the day at the car dealers, so here's some shots from Alaska:

Sea Otter (Enhydra lutris), Resurrection Bay, AK 8/4/2012

This Sea Otter (Enhydra lutis) entertained our tour boat in Resurrection Bay for several minutes, rolling over and over, but otherwise just lounging at the surface. No matter how he rolled, however, he always seemed to want his feet out of the water.

Harbor Seal (Phoca vitulina), Kenai Fjords NP, AK 8/5/12

This little Harbor Seal (Phoca vitulina) really isn't stuck. He can be in the water in seconds if he wants to. But this was a pretty uncommon sight -- most of the Harbor Seals we saw looked like this:

Harbor Seal (Phoca vitulina), Kenai Fjords NP, AK 8/4/12

Yes, that's ice, fresh off of Northwestern Glacier!

So what's up with these odd behaviors? Energy! Specifically, they're both ways to save it. In the otter's case, their fur is an astonishing insulator, which allows them to live as the smallest marine mammal in the area despite not having a blubber layer, even in 40-degree water. (That's Fahrenheit, just to be clear.) But, if you look closely at their feet, you see that the fur there is very thin, and what's more, the feet are webbed to increase the surface area to make them more effective for swimming. But increasing the surface area increases the rate at which they lose heat to their surroundings, and even if the air is a bit cooler than the water, the higher specific heat of water means you'll lose heat faster if you stay in the water. So, if you're an Alaskan Sea Otter, you do what you can to keep your feet up when you're lounging about.

The Harbor Seal's, though, are a bit of a puzzle -- ice is definitely not a thermally advantageous surface to rest upon, and yet they swim miles out of their way to rest there! Of course, they do have all that blubber, but they still have to swim there and there doesn't seem to be any advantage to it.

 

Turns out, of course, that there is an advantage to ice -- it floats! Tidal ranges on this coast can run over 10 feet, and Harbor Seals aren't exactly suited to rock climbing. So that poor guy hauled out on the rocks is going to get kicked off by the waves soon, and he'll have to find a new spot. Then when the tide recedes, he'll have to either move or be left with a long, steep climb down to the safety of the water. The guy on the ice can simply let his bed follow the water, and that means he won't have to move for hours -- quite the savings, apparently.

Here's a test case for that idea:

Steller's Sea Lion (Eumetopias jubatus), Kenai Fjords NP, AK  8/5/2012

These are  Steller's Sea Lions (Eumetopias jubatus). Although they don't look much like Mountain Goats, they're surprisingly good rock climbers. Helps to have front and rear feet that support you! Here's a closer look at a female:

Steller's Sea Lion, Kenai Fjords NP, AK  8/4/2012

In three days on the water, I never saw Sea Lions on the ice. If you're capable of climbing your way up above the high tide line and back down again, there's no reason to swim all the way up the glacial fjords to find that summer ice.

Energy may be the thread that ties these behavioral adaptations together, but the fact that these critters have to do such things is a reminder of something else. Natural selection has produced the amazing features of so many creatures, including these delightful marine mammals. But the fact that these animals have to practice such surprising behaviors to survive here shows quite plainly that natural selection isn't all-powerful, and it takes time. For now, Sea Otters and Harbor Seals are imperfectly adapted to their habitat, even here in the heart of their ranges. Critics of evolution sometimes harp on a mythical lack of transitional forms -- when in fact every species now in existence is either a transitional form or well on its way to extinction!