Where Do Orcas Find Drinking Water? (How Many Fish Do Orcas Need; Part Three)

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Orcas are beautifully adapted to life in the marine environment, but unlike fish, they are not able to meet their water needs by drinking seawater. Sources of fresh water are limited to coastal river inputs and subsurface springs, and although it is unknown at this point to what degree orcas or other whales can utilize those sources, they are certainly not able to rely upon them. So, how do orcas survive without fresh water?

Whales and dolphins have undergone some adaptations to cope with the marine environment- their kidneys are able to remove some of the excess salt that is inevitably swallowed, and their rubbery skin presents a good barrier which helps keep salt out. But there are really only two known ways that the fish eating orcas can get water; one is through the fish and squid they consume, and the other is by using their fat stores.

All vertebrate animals maintain their bodies at about the same salinity, which is a quarter to a third of the salinity of the ocean – so when the orcas can find enough fish, presumably they don’t need any other source of water. When fish become scarce though, the whales use their own blubber for energy, and one byproduct of breaking down their fat is water, at least enough to get by.

Like any other system that uses energy, there is a net loss when the whales don’t have enough to eat – in other words, there is loss both in storing the fat and then using those reserves later to provide sustenance and water. For the orcas, any shortage of fish is also a shortage of water, leaving them in a doubly precarious situation if the shortages extend for any great period of time.

Research on baleen whales indicates that those animals may need 30% more krill (which is saltier than fish) than previously thought when the problem of salt balance is taken into account. Even though orcas are completely different animals from the baleen whales, it does stand to reason that their need to obtain water from fish may drive both the type and the quantity of salmon needed to provide them with both water and nourishment.

J40 catches a salmon off False Bay, September 8, 2008 (CWR photo by Astrid van Ginneken)

“Water, water everywhere, nor any drop to to drink”. (From Rime of the Ancient Mariner by S. Coleridge)

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