Saltwater's effect on cetaceans.

Can whales sense any differences between saltwater and fresh? It seems to me that the effects on their bodies would at least be uncomfortable, and turning back to brackish water would ease that discomfort.

Of course. Salt water tastes completely different to fresh water.

Why would it be uncomfortable? Whales aren’t fish, and while their skins may not be as waterproof as most mammals it’s still fairly salt impermeable and they lack the gills through which fish suffer a lot of osmotic stress. There’s no particular reason I can see why whales would find fresh water uncomfortable.

On the contrary many whale species migrate into freshwater to gain relief from parasites and predators and they show every sign of showing great comfort from fresh water.

I worked at an amusement park one summer that had a dolphin show. While the dolphins clearly found the size of the tank (~20m in diameter and probably about 8-10m deep) they didn’t seem to be bothered by the barely saline content of the water, and in fact I’d assume that this was selected as being optimum for their health during the summer. There are several dolphin species that regularly live in moderately brackish river water. In general, marine mammals have a number of adaptations that allow them to cope with the high salt content of seawater, but as Blake points out, they aren’t adapted to absorb oxygen through the water and excrete salts the way branchial marine animals do.


According to wildlife experts, the freshwater has a very detrimental effect on whale’s skin.
The mother and baby whale swimming up the Sacramento River show these effects, of which a symptom is sagging skin. Also, cuts on the skin are slow to heal.
Scan down about seven paragraphs.

It’s no mystery that many whales suffer health probelms as a result of prolonged exposure to “fresh” water, but that’s no different to a the health problems experienced by a human who is exposed to water or sunlight for prolonged periods. Nonethless humans don’t find either water or sunlight uncomfortable until well after they start becoming harmful. In fact as with whales and fresh water most humans actively seek out both water and sunlight for comfort and relaxation.

That’s probably the best way to think about this. The effect of fresh water is equivalent to a sunburn in a human. Humans can sense sunlight perfectly well yet still find it comforting and actively seek it out, and so it is with many whales and salt water. And just as with humans and sunlight the problem comes with overexposure, not with immediate exposure. Moderate exposure is comforting, not uncomfortable.

Thay can almost certainly sense the difference in density, since it affects their buoyancy. Not that this should be particularly difficult to cope with.