A great tragedy has been unfolding for some time now in the North Sea, where a large pod of sperm whales have lost their lives. Whales have been stranded on the coasts of the Netherlands, the UK, France and Germany, and the known death toll as of February 3, 2016 has reached 28 sperm whales (just today 2 more stranded sperm whales were discovered in Germany). These strandings and resulting deaths represent a huge blow to the sperm whale population, and although many whales have been stranded alive, no efforts have been made to rescue any of them. Among numerous arguments and rationalizations against any kind of rescue attempts, one in particular, stands out, as it has been repeated many times, even by so-called reputable media sources, and could be considered the main reason for the lack of attempts to rescue these magnificent mammals. This argument concerns the notion that the weight of a beached whale crushes its internal organs, leading to certain death. For examples of this argument, see the quotes below:

Whales’ enormous mass is normally supported by water. When they are beached, the weight of their bodies damages their internal organs and muscles. New Scientist

or

Rob Deaville, from the Cetacean Strandings Investigation Programme — which examines all whale, dolphin and porpoise strandings in the UK — said once out of water the whales’ organs would have compressed, causing them to die. “When they were in the water the weight would support their organs, but unfortunately when they’re stranded alive they get compressed and that causes death fairly quickly,” he said. BBC News

or

“These animals were in good body condition but in the process of stranding became crushed under their own weight, which sadly led to their death.” BBC News

But is this true? What kind of pressure from a whale’s weight are we talking about? We asked a physicist to clarify this for us, and here are the resulting calculations:

1. Not considering a whale’s weight

The pressure on whale’s organs in a liquid like water is: P = PA + ρgh where ρ is the density of the liquid (in this case ρw = 1000 kg/m3 ), g is the acceleration due to gravity ≈ 9.81 m/s2 and h is the whale’s depth in the liquid. Therefore, the pressure on his liver at a depth of 3000 m in water is: P = 101325 + (1000)(9.81)(3000) = 29,531,325 Pa Now, what is going on when the whale is stranded? When the whale is on the beach, the pressure on his organs is simply atmospheric pressure, i.e. P = PA = 101, 325 Pa

2. Considering a whale’s weight

The addition of the pressure on the organs (like liver or heart) due to the whale’s own weight will be insignificant to the overall pressure on the organ. To see this, we can approximate the pressure on the heart or liver as being atmospheric pressure plus the pressure due to the weight of the whale pressing down on the liver, i.e P = PA + Pw. The atmospheric pressure is PA = 101, 325 Pa The pressure on his liver due to his weight is given by Pw = F/ A where F is the force pushing down on the heart (or liver, or any other organ), in this case the portion of his weight W = mg pushing on the liver or heart (let’s be generous and say it’s the whale’s full weight even though it will probably be half or some other fraction of this) and A is the area of the heart or liver(let’s say sperm whale’s heart is 2 by 2 meters, 185 kg). Then the pressure due to his weight (let’s say 20 ton) is Pg = mg /A = 20000(9.8) /4 = 49,000 Pa As you can see, this is only a tiny amount when compared to the atmospheric pressure (and is probably even smaller if we used the correct proportion of weight that is pushing on the liver or heart). Including the force due to his weight will only change the pressure from 101,325 Pa to 150,325 Pa. The reason that this is because the weight of air from above the whale that is pushing down on his liver (or heart) is substantially larger than the proportion of the whale’s weight that is pushing down on his liver or heart (the atmosphere is surprisingly big, heavy thing!). The pressure from whale’s weight will have an even smaller effect in water since we add an additional ρgh (this is again because the weight of water above the whale will have a far greater effect on his organs than the weight of the whale above his organs!). Including the pressure due to the whale’s weight, the pressure on his liver or heart at a depth of 3000 m in water is P = 106225 + (1000)(9.81)(3000) = 29,536,225 Pa and the pressure on his liver at a depth of 250 m in water is P = 106225 + (1000)(9.81)(250) = 2,558,725 Pa which is only a tiny change compared to the previous results.

The table below demonstrates that whales are exposed to incredible amounts of pressure, not only at deep dives but also even at “shallow” 250-meter dives.

Next, we need to consider how much time free-ranging sperm whales actually spend diving per day. The study by Watwood et al. (2006) that involved tagging sperm whales revealed that they spend “more than 72% of their time in foraging dive cycles.” In other words, not only are sperm whales exposed to at least 2,602,825 Pa during “shallow” dives on a regular basis — they actually spend most of their day diving!

But what about other species? Humpbacks also dive up to 250 meters, and similarly, fin whales spend a lot of time diving to depths of 400 meters (see the diving profile of the fin whale below).

Image from Tethys.org

What all of this means is that whales, both “shallow” diving species like fin whales or humpback whales and deep-diving whales like sperm whales, are no strangers to pressure. They are not only exposed to great pressure during shallow, 250-meter dives but are also exposed to these pressures on a regular basis.

Furthermore, the amount of pressure they are exposed to when stranded cannot compare to what they routinely experience while diving; hence, the argument that beached whales’ own weight crushes their internal organs, leading to their deaths, is not only incorrect but also absurd! Even shallow-diving species are exposed to a 10-fold pressure while diving compared to what they would experience if they were beached.

Finally, we challenge allegedly reputable news sources such as the BBC and New Scientists as well as those who have been interviewed and insist on the accuracy of the weight argument to refute the argument that has been made here.

References:

Watwood, S. L., Miller, P. J., Johnson, M., Madsen, P. T., & Tyack, P. L. (2006). Deep‐diving foraging behaviour of sperm whales (Physeter macrocephalus). Journal of Animal Ecology, 75(3), 814–825.