Why are whales so big?

While on holiday in the Eastern Cape of South Africa, I stumbled across a dead humpback whale on the beach. I was immediately struck by…the smell of course (because it had been dead for a few days when I found it). Once I got over the olfactory shock I was impressed by the size of the creature! Take a look at this short clip of the moment I stumbled across it:

In the photograph below you can clearly see that it is lying on its back:

The dead humpback whale on a beach in South Africa.

According to wikipedia:

The humpback whale (Megaptera novaeangliae) is a species of baleen whale. It is one of the larger rorqual species, with adults ranging in length from 12–16 m and weighing around 25–30 t. The humpback has a distinctive body shape, with long pectoral fins and a knobbly head.”

I estimated the humpback whale on the beach to be approximately 12m, and I was indeed struck by the length of the pectoral fins. Take a look at the size of these fins!

I estimated the pectoral fin to be approximately 2.5 – 3m long.

I am not certain what killed the whale, although it could possibly have been hit by a large ship or vessel. According to wikipedia again these magnificent cetaceans travel long distances to get to their feeding or breeding grounds.

“Found in oceans and seas around the world, humpback whales typically migrate up to 25,000 km (16,000 mi) each year. They feed in polar waters, and migrate to tropical or subtropical waters to breed and give birth, fasting and living off their fat reserves. Their diet consists mostly of krill and small fish. Humpbacks have a diverse repertoire of feeding methods, including the bubble net technique.”

Below, you can clearly also see the baleen that they use to filter their tiny prey. The dense hair reminded me of porcupine quills, while the inside structure was like a plastic accordian (though it’s made of keratin in the whale).

Accordian baleen.
Porcupine of the sea!

In the past, the humpback whale was a target for the whaling industry and the species was once hunted to the brink of extinction (like several other whales). According to wikipedia, the population of humpback whales “fell by an estimated 90% before a 1966 moratorium”. Since then the number of humpback whales has “partially recovered to some 80,000 animals worldwide”, but entanglement in fishing gear, collisions with ships and noise pollution continue to affect the species”. Although I did not notice any obvious injury to the whale, it was on its back, so I could not tell whether it had been hit by a ship or not.

As for why whales get so big? My guess is that there are at least two reasons. Firstly, creatures living in water can grow larger because their bones do not have to support as much weight as land mammals living in less buoyant air. Secondly, because water conducts heat away from the body much quicker than air (air is a good insulator), the animals must generate significant fat reserves to maintain their body temperature. A large body also increases the ratio of the internal volume to the surface area, which serves to further reduce heat loss. You do not find many mice-sized mammals living permanently in the ocean!

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