The answer is most definitely A.

First, there is nothing wrong with the example sentence grammatically, so that makes it the best choice before even looking at the other answers.

As for C, it is not the right answer because the pronoun 'its' in the second part of the sentence is ambiguous. Is 'it' referring to cod, hassock, or monkfish? Also, 'but not monkfish' is problematic. It should read 'unlike monkfish' or something of that nature. The meaning of the sentence is unclear because it is not saying concisely that monkfish are being depleted by overfishing because of the lack of legal fishing limits.

Danielle,
In the following sentence...
C.There are legal limits on the size of cod and haddock that can be caught, but not for monkfish, which contributes to its depletion through overfishing.

does which refer to monkfish or caught?

Thank you Danielle and sochatte,

I thought "as" is awkward in "A"

and I thought ",which"is problematic in "C"
because it refers the whole situation, the usage cannot be accepted in GMAT.

If there's nothing wrong or awkard with "as" in A,
Then I'll choose A also.

Thank you.

Danielle,

I am not convinced with the answer choice "A". Here is my take:

If we break sentence "A" using spoiler, then:
"There are no legal limits, as there are for cod and haddock, on the size of monkfish that can be caught, a circumstance that contributes to their depletion through overfishing.

If you see, how can "their" refer to monkfish as monkfish is singular, further "their" can refer to "cod and haddock" as two singular nouns combined together to make plural. But "their" cannot be referred to "cod and haddock" as the depletion through fishing is in reference to monkfish.

That is why my preference is "C" as the other 3 B, D and E are totally out.

Please advise.

Thanks

Sochatte, 'which' refers to the legal fishing limits -- neither 'monkfish' nor 'caught'.

Nobody29, there is nothing awkward about the usage of the word 'as' in example A. In fact, that is model usage of the word 'as'.

Jan08, A is the answer. 'Monkfish' is plural, because fish is a word that is the same singular and plural, and here refers to the whole species of monkfish, which is more than one fish.

Thanks Danielle.

No worries jan08.