Hello.  I'd like to know how a whale's body is affected by swimming in fresh water.  A few whales have swum up & down rivers in the past few years, and I was wondering how their cells handle the osmotic imbalance that I assume would be present.   Also, I've heard that there is a beluga population in the St. Lawrence river.  Are these permanently there, or do they venture out into the ocean as well?

Hi Bruno,

Belugas are indeed found in the St Lawrence, although this system is a big patch of water and I'm not sure how far upstream any of the species found there go (i.e. not sure that any of them enter fresh water). There are of course several species of freshwater dolphin that do live in rivers, but none of them in Canada. For more information about whales and dolphins in the St Lawrence you should have a look at this site.

http://www.whales-online.net/eng/FSC.ht … 1-3-2.html

As for the question relating to the effects of fresh water on a whales body, I may be wrong (if so someone please correct me!) but i think the osmotic challenges may be less than imagine. Moving from freshwater to saltwater (or vice versa) does require particular physiological strategies in fish, but to a large extent this is because of the way in which they transfer gases and salts across the permeable membranes of the gills. For cetaceans this won't be an issue. Perhaps someone will have more info on osmotic issues, but I expect that the problems whales seem to have when they find themselves up rivers are more to do with them being confused, stressed and lost than their salt balance.

I think another big problem they have is reduced buoyancy (since freshwater is less dense than saltwater). This means they have to use more energy to swim and surface, which exhausts them quite quickly.