Really big sharks

Could a shark theoretically exist at the size of a blue whale? Blue whales are apparently the largest animals to have ever existed, at 30 m long and 200 tons weight. There are many species of sharks, but I'm interested in species such as Great White sharks that are capable of attacking and feeding on large animals such as seals, squid etc.

Basically I'm wondering if an animal that feeds on squid and fish could survive if it was as large as blue whale, or if only baleen animals can survive at that size.

• As long as the prey grows in size, the predator will too. Remember these large sharks tend to be warm water creatures and a global cooling trend effects them heavily. – Twelfth May 11 '15 at 23:09

sure.

Blue whales get up to 30m long. Fiction should have no trouble reaching that size, as nature got you at least half way there. The Megalodon was estimated to be 18m long.

And it's a whole lot bigger when the fisherman tells the story!

The main problem isn't the theoretical maximum size of the animal (as hinted already, that can be achieved in earth gravity).
It's keeping the animal in food. A blue whale is a slow filter feeder, gulping up tons of plankton while slowly swimming through the water.
Sharks are active hunters, would need very large prey items if they get that large.
And that means an entire population of megafauna in the oceans. Such of course existed at the time of megalodon. And that one died out when the saurians it preyed on died out.

So your ecosystem would have to be such that megafauna exists, and has the plant and animal life for it to feed on, in order to sustain the shark population.
The few blue whales (and other large whales) in our oceans will probably not do, they're too few and far between to provide reliable sources of sustenance to a viable population of megasharks.

• Your distinction isn't entirely accurate: the whale shark is a large filter feeder (hence the whale part). It just happens to be a fish rather than a mammal. – Isaac Kotlicky May 10 '15 at 13:51
• @Isaac Kotlicky: I think the distinction between Megalodon = predator and whale shark = filter feeder is important, since the OP was explicitly looking for a predatory shark. Whale sharks, like whales, can become larger because they are grazers. You can see this with ichtyosaurs and cetaceans, as well as with land animals. – jamesqf May 10 '15 at 18:21
• @jamesqf OP added the predatory requirement later. Anyhow, no reason we can't evolve the existing whale shark into an active predator... – Isaac Kotlicky May 10 '15 at 18:46
• @Isaac Kotlicky: I always had the predatory requirement in the question. I put it there because I knew people would suggest larger versions of whale sharks and similar. I really just wanted to know if it was possible to have a predatory animal of that size – JessWelch May 11 '15 at 1:10
• @JessWelch my mistake then... – Isaac Kotlicky May 11 '15 at 1:17

There would have to be a reason for a shark to get to that size, but there isn't one on Earth today. Sharks are successful hunters, and thrive at their current sizes unless impacted by change in climate and human intervention.

So, if you place a large number of extraordinarily sized prey (or large volumes that require a large mouth), then it would make sense to me to have a large predator like a shark.

There are things like the megamouth shark today. Cetations evolved filter feeding from the same ancestors as toothed whales. You just need to find a tissue that can be deployed for the purpose. Mammals don't have gills anymore so there are "gill arch" structures that can be reused. Fish already transformed some gill arches into jaws and ears. Some fish have a second set of jaws in the throat, so that suggests something that could turn into a filter.

Then you need adaptive radiation to promote rapid evolution. A completely new environment or other major factor that affects the lifestyle would allow rapid transformation, as cetations did at breakneck speed (an extreme case) when they returned to the sea.

Filter feeding would then promote large body growth to be more effective at it.

Blue whales are proof that sea life can get that big. With a little genetic tampering, there is no reason we couldn't militarise a whale into a kick-a 100 foot pseudo-shark. Add teeth and abrasive skin, give it keener hunting senses and a bad attitude. Whales are already used to eating all the time, so you're halfway there.

• @theonlygusti - your suggested edit on here was approved by the Community user as a result of a reviewer deciding to further edit your suggestion. As a general rule, small edits such as that are unnecessary. – ArtOfCode May 9 '15 at 19:29