Sea mammals and fresh water

Have you ever wondered if sea mammals drink sea water from the ocean?  Or do they require fresh water to survive?

According to Dr. Sara Iverson, an expert in marine physiology and a Professor of Biology at Dalhousie University in Halifax, Nova Scotia, they do require fresh water, but they get it in a different way than we do.  

There are basically three ways to obtain water.  Drink it directly, get it from the water content in the food one eats, or the body produces it as food is metabolized (broken apart).  Marine mammals rely mostly on these last two ways to get their water.

Piscivores, those who live on eating fish, can acquire all of their water needs through their food, since fish have a high water content.  When they swallow fish as they eat, they do swallow some sea water.  Their kidneys are much more complex than the kidneys of a human, and they are able to expel these high amounts of salt and keep a correct chemical balance.

Some mammals, like the grey seal, go through periods of expected fasting.  When they give birth, it is in a place where they cannot eat or drink.  To get ready for this event, they bulk up.  While they are giving birth and then nursing for about 16 days, their bodies metabolize this stored fat.  During metabolism, the conversion of one gram of fat produces 1.07 grams of water!

To listen to this story, go here. It is the fourth story of the bunch.

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In a related story, black bears hibernate for four months.  During this time, it does not eat or drink, nor does it urinate nor defecate.  The bears get enough water to remain healthy as they metabolize their fat. And then it emerges four months later with its blood chemicals balanced and without losing any protein.

In preparation for this hibernation, they start gorging in the summer on carbohydrate-rich foods and can gain 30 pounds a week.

Other hibernating animals wake every few days to eat and pass wastes, but black bears don't rouse the entire time they are hibernating unless disturbed.

This next bit is a little off topic, but while I was double checking the story above, I ran across this funny, true story.

"The heart rate, which is usually between 40 and 50 beats per minute while asleep during the summer, drops to around 8 beats per minute while hibernating.
 
"Black bears keep their heads and torsos warm enough that they can wake if disturbed, though some may take awhile to do so. In a 1981 article in Natural History, Rogers told of the time he accidentally fell onto a six-year-old female in her den. Even though her cub bawled, she didn't wake up for at least eight minutes. On the other hand, some individuals can revive disconcertingly quickly. Rogers again:

"On January 8, 1972, I tried to hear the heartbeat of a soundly sleeping five-year-old female by pressing my ear against her chest. I could hear nothing. Either the heart was beating so weakly that I could not hear it, or it was beating so slowly I didn't recognize it. After about two minutes, though, I suddenly heard a strong, rapid heartbeat. The bear was waking up. Within a few seconds she lifted her head as I tried to squeeze backward through the den entrance. Outside, I could still hear the heartbeat, which I timed (after checking to make sure it wasn't my own) at approximately 175 beats per minute."

Now you've heard something interesting.