Let's consider the following sentence, which I just found in Google as an illustrative example:
Наиболее опасные из акул – тигровые акулы, которые обитают в тропических водах.
Two interpretations come to my mind:
(1) The most dangerous sharks are the tiger sharks, which live in tropical waters.
(2) The most dangerous sharks are the tiger sharks that live in tropical waters.
Sentence (1) contains a non-restrictive clause and says two separate things, the first one being that the most dangerous sharks are the tiger sharks, and the second one being that the tiger sharks live in tropical waters. Sentence (2) contains a restrictive clause and says only one thing, namely, that the most dangerous sharks are those tiger sharks that live in tropical waters. Sentence (2) implies that there are also tiger sharks that live in other waters and that those tiger sharks are less dangerous.
My question is this: Are clauses with который restrictive or non-restrictive by default - that is, in situations where the meaning of который is unclear from the context? In other words, which meaning should be assumed when the context allows both?