Eating one whale every three thousand days?

My current ongoing project, about which I've asked many questions, is about a world in which evolutionarily plausible legendary and folkloric creatures roam the Earth. One such creature is the sea serpent. In my world, sea serpents are giant relatives of moray eels which use constriction to kill their prey, large whales.

Note: pretty much every figure I give below is only roughly so, so just pretend I've put the word "about", "roughly", or "approximately" before every number.

If I assume a grey whale is cylindrical, then it has a diameter of 4 metres, and therefore a circumference of 12 metres. If the serpent is to wrap itself around its grey whale prey 3 times, then it needs to be at least 36 metres long. I'll add 6 metres to account for the head and tail. To decide how wide it would be, I copied the proportions of a different constricting predator, the boa constrictor (who is 40 times longer than he is wide), and concluded that a sea serpent is 1.25 metres thick.

Again assuming a cylinder shape but this time for the predator (which is reasonable given that it's an eel), I calculated a volume of 224 $m^3$. A marine animal needs to be roughly as dense as seawater so that they don't sink or float too much, so the sea serpent will have a density of 1020 kilograms / m^3. Now with both volume and density, I can calculate mass, and end up with... 230,000 kilograms. Well above that of a blue whale. Since I've been very rough in my maths, I'll knock off the 30,000 to cut down on mass, but I'm still over blue whale size.

The basal metabolic rate (in kilocalories per day) of an organism is given by $K \cdot M^{0.75}$, where K is a constant depending on the kind of organism and M is the mass in kilograms. K for a fish is 10. So, $10 \cdot 200000^{0.75}$ gives you 95,000 kilocalories per day. A guy on r/theydidthemath calculated that the total blubber of a large bowhead whale contains 291,000,000 kilocalories, so - therefore - a sea serpent needs to eat a whale once every 3 thousand days (or a liitle more than 3 thousand days, of course, since there'll be more than just the blubber to eat).

Now finally to my question. One whale every three thousand days... sounds like a lot. I mean, for the ecosystem. Is that too much of a blitzkrieg for the local whale populations to handle? Is one whale every three thousand days per sea serpent sustainable for the local ecology?

posted over 5 years ago

SealBoi‭

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