PT16.S2.Q16 - researchers in south austrailia

Not Ralph Nader

Hi fellow 7Sagers, while commenting on the September Discussion, I would be thankful if someone can explain to me why answer choice C is wrong and E is right. It would be great if you could explain to me what exactly CPUE mean in the context of the question

Sami

Hey Nader, I just took a look at the question. CPUE means the number of fish, in this case sharks that are caught per hour for each km. The premise is that number of sharks caught with that measurement, i.e, CPUE, has remained the same since 1973, so the population of Sharks has also remained the same since 1973.

The problem with the argument is that its assuming that what was true in 1973, in reference to how sharks are caught, hasn't changed from that time. So if we wanted to weaken this conclusion that shark population is approximately the same since 1973, we want an answer choice that will say something that will affect the measurement and that is important to how the sharks are being caught has changed in between that time.

Answer choice "E" brings that issue forward. If the technology has improved since 1980, and more sharks are being located, that it's not true that just because the same number of sharks are being caught, the population of sharks is actually the same.

Answer choice "C" can be applied to both time, 1973 and today. So we don't know if "incidental mortality" is not constant anymore. For all we know it caused the same amount of mortality in 1973 and is still causing the same number of deaths in sharks today. So the two time periods are still similar with incident mortality applied and we can still conclude the sharks population is still the same from 1973.

I have found when it comes to questions where something about time has changed from premises to conclusion, to weaken it you want to say that something essential to the conclusion has changed between that time. To strengthen it, you want to say that nothing has changed from that time that is essential to the conclusion. For example one way to strengthen the conclusion is that in between 1973 and today technology has not gotten better that allows us to catch fish with more accuracy.

Sami

Also, I think if this stimulus was a flaw question, the answer choice would be takes what was essential to the number of sharks being caught in 1973 has not changed since then.

Sami

I just want to add one last thing about the stimulus, it might help to see this as an analogy. 1st fact: A (1973) had C (# of sharks being caught) . 2nd fact: B, which is time today, also has C (same # of sharks as 1973. So our conclusion is: D, the population of sharks is the same in A and B.

It assuming that because A and B have C they are similar and therefore have the same D. to weaken it you want to poke holes in similarity between A and B. If A and B had something essentially different like B had better technology, then we can no longer say that just because same amount of Sharks, "c" are being caught, which is measured by CPU, then D is same for both time.

Our similarity between the two time 1973 and today falls apart, And we can no longer say that what was true in 1973 about the population of Sharks is also true today just because they have "C" in common, which is the same number of sharks being caught.

Let me know if I sucked at explaining it.

Not Ralph Nader

@Motivated thanks for explaining the question in such details, and you are great at explaining it. I can see how other answer choices are totally wrong including C.

HopefullyHLS

@Sami thanks so much for your explanation! Classical example of how LSAT knows what kind of assumptions humans make

I also wrongly went for C, although not entirely sure how it wrecks the argument. My process of thought was that if CPUE is, let's say, 5, then this number is projected to the whole sea volume and thus an approximation of the population is won.

But if technological improvement led to an increase of the fish catching rate from, let's say, 5% to 10%, then a CPUE of 5 would lead to a population measurement of 100 in 1973, but only 50 now.

Now I also see that C does absolutely nothing to weaken the argument, since all sources of fish mortality are already included in the CPUE (it's basically kind of projecting a sample to calculate the approximate fish population).

Clemens_

PT16 S2 Q16: South Australian Sharks

(P1) Researchers estimate the size of South Australian shark populations by monitoring the number of sharks that commercial shark fishing boats capture per square kilometer of extended net per hour.
(P2) Between 1973 and the present, this capture rate has remained constant.
(C) Therefore, the size of the shark population in South Australia has also remained constant since 1973.

We are supposed to weaken this, i.e. show that this estimate of a constant shark population size might be mistaken. Under timed conditions, I tried to anticipate the introduction of an alternative cause that might also affect shark populations (e.g. climate change, invasive species, some kind of shark disease etc). Thus, I chose (C), as (C) indicates an alternative cause of decreased shark populations (accidental shark capturing by other types of fishing). Retrospectively, however, this was naive: Even if there were some alternative cause of shark population decreases, why would the capture rate remain constant? (C) furthermore has the problem of not explaining why this alternative cause of shark deaths was not also present in 1973; i.e. (C) does not explain why this alternative cause of shark deaths should be more pronounced in the present than in the past.

The correct answer for this question is (E): The commercial shark fishing boats have become able to locate the sharks with greater accuracy. But how is this improvement in finding sharks supposed to weaken the argument? Regardless of how good the shark fishermen might have become at locating the sharks, we know from the stimulus that they have not increased the number of sharks captured per square kilometer of net per hour. Is the idea that the shark fishers now NEED to identify specific shark habitats to capture x number of sharks, whereas they in 1973 could simply target any given area in South Australia? Or is the idea simply that the shark capture rate would have declined in the absence of better shark locating technology; i.e. is the cause for the constancy in the capturing rate not the postulated constancy in the shark population but rather the fact that better technology now allows fishers to locate individual shark DESPITE a decreased overall population? I assume that it must be this latter point, though I am still not 100% as to how exactly (E) is supposed to work.