Q13 - When so many oysters died off the coast

[Laura Damone]

Question Type:
Explain a Result

Stimulus Breakdown:
No argument here so we just need the facts: A British oyster die-off that left a speicies close to extinction was correlated with an increase in water temp that was first thought to be the cause of the die-off. But the actual cause was the chemical TBT. TBT was banned and now it's virtually eliminated from British waters, but the endangered oyster population hasn't grown.

Answer Anticipation:
For Explain a Result questions, it can be helpful to use this exercise to both wrap your head around the facts and anticipate an answer. Fill in the blanks: "How come _____, in spite of _____, because I would have expected ____." So, how come the oyster population didn't bounce back in spite of the fact that the cause of the die-off was removed, because I would have expected the population to grow. Well, maybe so many oysters died off that there aren't enough to breed the population back up. Or maybe the oysters that didn't die off were sterilized. There's a lot of ways to skin a cat, as they say, so when there isn't a clear explanation that the stimulus suggests, stay flexible in your anticipation and your answer choice evaluation.

Correct answer:
C

Answer choice analysis:
(A) So what? The stimulus debunked any causal link between warm waters and the oyster die-off, so the slowing of the temperature rise doesn’t help us explain anything.

(B) Now, if this had said that the oysters relied on the same food sources as the barnacles, then we'd be on to something, because the barnacles, now free to barnacle about in TBT-free waters would be a new source of competition for food. This, in turn, might prevent the oyster population from bouncing back. But alas, this answer says the two species feed on different foods, so this answer eliminates a possible explanation rather than providing one.

(C) What kind of oysters is our stimulus concerned with? Native ones. Did you notice that at the outset? Maybe not, in which case this is an easy answer to mistakenly eliminate because it might seem like an irrelevant comparison. What's more, this answer is about what TBT did, and TBT is gone, so there might appear to be a temporal issue here to boot. But in fact, if TBT killed imported oyster varieties that flourish in the warmer water at the expense of the native population we're concerned with, we can infer that these imported oysters are recovering since the TBT is gone, thereby threatening our native species and preventing its population from bouncing back.

(D) Anything that has little effect on the oyster population is unlikely to explain something about the oyster population.

(E) The conditions in which TBT is more or less deadly is irrelevant because it's out of the ecosystem.

Takeaway/Pattern:
Some Explain a Result questions are intuitively predictable. Others, like this one, not so much. Don't get thrown if you can't come up with a good prephrase. Just make sure you know the unexpected result you're trying to explain and why it's unexpected. That will give you the information you need to evaluate the answer choices. If you do come up with a good prephrase for one of these tricky ones, stay flexible. Don't nix answers just because they don't match your prephrase. Always evaluate each answer on its own merits.

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