There are types of freshwater river dolphins in the Yangtze (well, one of these species probably is extinct there as of recently but still) and the Amazon, for example. Sea dolphins can survive in freshwater for awhile but their skin isn’t adapted to it, and it will get damaged eventually. That and the difference in buoyancy in sea water vs freshwater leads to the sea dolphins eventually getting exhausted in freshwater.
this post was submitted on 21 Jan 2024
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Not in the Yangtze anymore :(
There is still a bit of the Finless Porpoise left there, but not dolphins specifically no.
They probably cut the fins off to make soup.
I would think marine mammals are also adapted to the level of salt in their diet. So not just food abundance but its salt content could be important.
That said, I know orcas like to drink freshwater if they can get it. So salinity may not be required. Their adaptations are likely built around eliminating salt, and therefore may not be stressed at all by low salt food.
Yeah from my brief reading it seems they can adapt to food salinity by altering their urine concentrations so I don’t think that’s a huge factor, at least it’s not something that comes into play before the other factors begin to harm them. But if you could fix their skin and buoyancy, diet may start to matter. But their prey is also a different salinity than the water it lives in a lot of the time, and sometimes they eat land animals like birds and such ofc.
Orcas rely on the salt in the water to keep their skin healthy. If they stay too long even fresh water they will succumb to infections. Other types of dolphins seems to be able to adjust a little better to shifting amounts of salt in the water. I have no clue about the larger whales but I suspect they have problems with fresh water because they wont float as easy in it.
Good call on buoyancy! Swimming in fresh water would probably feel like us walking in knee high mud.
Seals and sea lions come up rivers all the time, what matters is the food sources.