Learn Portuguese (Portugal): O crocodilo morde com mais força do que a foca consegue aguentar. - The crocodile bites with more force than the seal can withstand.

Because the second half of the comparison is a full dependent clause with its own conjugated verb (consegue aguentar). In simple comparisons between two nouns or pronouns, you can often drop the do and just use que. However, when introducing a clausal comparative like this one, you must use the complete phrase do que.

Why use consegue for "can" instead of pode?

Conseguir emphasizes physical ability, overcoming a difficulty, or managing to do something successfully. Poder is typically used for permission or general possibility. Since surviving a crocodile bite is a matter of pure physical capacity and endurance, consegue is the natural choice.

Why use the phrase com mais força instead of just saying it bites harder (mais forte)?

While you could absolutely say morde mais forte (using forte as an adverb), Portuguese frequently uses the preposition com plus a noun to describe how an action is performed. Com força is a very common way to say "forcefully" or "hard," so making it comparative simply becomes com mais força (with more force).

Does a dependent clause after do que ever require the subjunctive mood?