Conclusion : In this way, the officials hope to stop the northern snakeheads from eliminating rare native fish species.

basically the presence of northern snakeheads threaten the survival of rare native fish species

this line is very important to eliminate option E
would removing Nothern snakeheads reduce the threat the northern snakeheads have on rare native fish species
we are concerned about evaluating only the threat posed by northern snakeheads on rare fish species



Only B and E come close but to get to the right answer apply the variance test

let's look at E

Whether rare native fish species in the region face any threats to their survival other than the proliferation of northern snakehead

if you answer yes there are some other factors affecting the survival of rare native species but if you notice northern snakeheads are still a threat to the survival of rare native species.

If you answer no you basically answer that snakehead are a threat to rare native species

that's how B wins How local population numbers of rare native fish species have been changing since the wildlife officials started paying recreational fishers to catch northern snakeheads

How removing the snakeheads affect the population of rare fish species
if the population did not change or decrease the conclusion falls apart

if the population increased then we know that northern snakeheads were a threat to rare native fish species

I am also inclined towards B and E.

In my opinion, by using variance test for option E, if answer is yes, rare native fishes are still endangered. In case of "NO", removal of snakehead fishes can eliminate danger to RNF or reduce the danger. In case of "No", answer is not polar opposite. it is quite blurry.

Similarly, for option B, if RNF is increasing, plan is working and if it is either decreasing or stagnant, plan is not working.

B seems quite close but I am not satisfied. Can someone reveal official solution?

Official Explanation

Evaluation of a Plan

In hopes of preventing the nonnative species northern snakehead from eliminating rare native fish species, wildlife officials have for the last three years been paying recreational fishers for each snakehead they catch. The northern snakehead has no predators in the area.

This question requires us to identify information that would be useful for determining whether the officials' plan will succeed.

Note that the plan has already been in effect. Nevertheless, we are given no information as to how well the plan has succeeded so far. To determine whether it is responsible to keep paying these fishers to catch northern snakehead, it is vital to understand whether the fishers' work up to this point has had any observable effect.

That is, it would be helpful to anyone who wants to determine whether the officials' plan is likely to succeed to have information about how the numbers of rare native fish species have been changing during that time.

A. This information would be useful for determining whether there may be alternative ways of reducing the northern snakehead population. However, it is not useful for determining whether the plan in question is likely to be successful.

B. Correct. As noted above, this information would be helpful in assessing whether the officials' plan is likely to succeed. If the numbers of rare native fish species have stayed constant or even declined throughout the period that the plan has been in place, it seems unlikely that the plan will ultimately be successful.

C. This information may provide a small amount of information as to how great a threat the northern snakehead might pose, but not much. For one thing, in its native region, the snakehead likely preys on different species from those in the region in question. More importantly, however, is the fact that this information is simply not useful to determining whether the officials' plan is likely to work in the region in question.

D. This might be useful for determining whether fishers have been motivated by the plan. This could potentially be useful for determining whether the plan will work; after all, the plan will not likely work if very few northern snakeheads are actually removed. Nevertheless, it is not as useful as noting the changes in the native fish population since the plan first went into effect.

E. Determining whether there are other threats to the rare native fish species would tell us whether the plan, if successful, is sufficient to save the rare fish species. Still, it is not useful in determining whether that plan is likely to be successful.

The correct answer is B.

VeritasKarishma GMATNinja could you please help how to chose B over E?

NS is not native and has no predators.
Plan: Pay fishers for each NS
Aim of the plan: Stop NS from eliminating rare native fish species

Which of the following is useful to determine whether the plan is working?

A. Whether the northern snakehead's population in local lakes and rivers could be reduced by introducing predators from its native habitat

Another plan is irrelevant.

B. How local population numbers of rare native fish species have been changing since the wildlife officials started paying recreational fishers to catch northern snakeheads

Correct. We can try to find whether the plan is having any impact on the population of rare native fish species. Since the plan came into effect, did their number increase. If yes, we know that the plan is working. If no, then the plan is not working (at least yet).

C. Whether the fish species on which the northern snakehead preys in regions to which it is native and in which it is abundant have become significantly depleted in recent decades

Regions in which NS is native is irrelevant.

D. What total number of northern snakehead have been caught by recreational fishers since the wildlife officials began paying for them

The exact number of NS caught is irrelevant. Whether the number of NS caught is having an impact on the population of rare native species is the point.

E. Whether rare native fish species in the region face any threats to their survival other than the proliferation of northern snakehead

Other threats are irrelevant. We need to know whether this threat is being contained. We need to know whether our plan is working - whether the threat of NS to the native fish species is being controlled.

Answer (B)
_________________

First discovered several years ago in North American lakes and rivers, the northern snakehead is a nonnative fish with no local predators. To keep the northern snakehead's population from growing, for the past three years wildlife officials have been paying recreational fishers for each northern snakehead they catch. In this way, the officials hope to stop the northern snakeheads from eliminating rare native fish species.

Key points -
1. the northern snakehead was discovered several years ago- fact.
2. for the past three years wildlife officials have been paying recreational fishers for each northern snakehead they catch-plan being implemented.

We have to evaluate the success of the plan which is already being implemented, so we are not asked to evaluate or propose new plans.

Options:
A. Whether the northern snakehead's population in local lakes and rivers could be reduced by introducing predators from its native habitat.
Proposes alternative plan, so not relevant.

B. How local population numbers of rare native fish species have been changing since the wildlife officials started paying recreational fishers to catch northern snakeheads.
Evaluates the current plan which is being implemented. Relates local population numbers of rare native fish species to the plan.

C. Whether the fish species on which the northern snakehead preys in regions to which it is native and in which it is abundant have become significantly depleted in recent decades.
Irrelevant to the discussion.

D. What total number of northern snakehead have been caught by recreational fishers since the wildlife officials began paying for them.
Tricky option. But even if we know the number of northern snakehead caught, how can we relate it to local fish population.

E. Whether rare native fish species in the region face any threats to their survival other than the proliferation of northern snakehead.
We are concerned only with the northern snakehead and not with other predators.

So only option B correctly links all the parameters, so B is the answer.

Our plan is to pay fishers to catch snakeheads, in order to save the native fish species.

B) vs E)
E) would tell us a little bit whether this plan is more likely to succeed, because the native fish species maybe has only one predator. But we still dont know whether the northern snakehead is that much of a threat and whether paying the fishers will work out in any way.
But B) tells us more. B) digs down to the core of our plan, especially how the population changed since we started paying. Wouldn't this tell us so much about the effectiveness of our plan?

First discovered several years ago in North American lakes and rivers, the northern snakehead is a nonnative fish with no local predators. - The snakehead is not native to the water bodies it was first discovered in. There are no local animals that prey on the snakehead.

To keep the northern snakehead's population from growing, for the past three years wildlife officials have been paying recreational fishers for each northern snakehead they catch. - Wildlife officials are trying to keep the snakehead’s population in check (since there are no local predators which could have kept its population in check). For this, they have been paying fishers per snakehead caught.

In this way, the officials hope to stop the northern snakeheads from eliminating rare native fish species. - The officials are going through this plan in order to try to stop snakeheads from eliminating rare native fish species.

Gist: The snakehead has no local predators. Wildlife officials hope to stop the snakehead from eliminating rare native species (goal). For this, they are trying to keep its population in check by paying fishers to catch snakehead (plan).



What data will help us evaluate the likelihood that the plan will succeed in achieving its goal?

In order to evaluate the plan, two questions come to mind:

• Is paying the fishers making a significant impact on the snakehead’s population growth?
• Is this impact helping reduce the decline of native fish species population?

Let’s understand these: what if the fishers are not incentivised enough to fish for snakeheads? Maybe the fish are too difficult to catch, or they can fish some other species that get them better returns. Or, even if the fishers are incentivised, the cumulative capacity of the fishers to fish for snakeheads is too low to make any meaningful impact.

What defines ‘meaningful’? What if the population of snakeheads is so huge compared with the rare native fish species, or what if each snakehead preys on a disproportionately large number of fish? In such a scenario, even if the snakehead population is stopped from growing, the goal may not be achieved.


A. Whether the northern snakehead's population in local lakes and rivers could be reduced by introducing predators from its native habitat
Incorrect. We’ve been asked to evaluate the likelihood that the ‘given plan’ will succeed. Whether another plan would work does not help evaluate the likelihood of success of the given plan.

This is a very common answer choice in a plan & goal question. Say John wishes to lose weight. In order to lose weight, he considers going on a keto diet. In order to evaluate whether keto diet will help him lose weight, we’ll not get into determining whether Atkins diet will work for him. Whether keto works or not is independent of whether something else works.

B. How local population numbers of rare native fish species have been changing since the wildlife officials started paying recreational fishers to catch northern snakeheads
Correct. Has there actually been an upward trend? If the local rare fish population continues to diminish, despite the plan being active, the plan will probably not be successful. On the other hand, if the local population has started showing growth (or stabilizing), the plan is probably working. Determining this would be useful to evaluate the likelihood that the plan will succeed.

C. Whether the fish species on which the northern snakehead preys in regions to which it is native and in which it is abundant have become significantly depleted in recent decades
Incorrect. This is a complicatedly worded statement. This option talks about the fish species on which the snakehead preys in its native regions. The option asks us to consider whether those fish species have become depleted. We need to evaluate whether the plan (to pay fishers to catch snakehead) will succeed. How drastically snakehead preys on other species, and how well the other preyed population is able to cope is immaterial.

D. What total number of northern snakehead have been caught by recreational fishers since the wildlife officials began paying for them
Incorrect. This answer choice might look attractive. An absolute number of snakehead caught, however, does not give us an understanding of the success of the plan.

Say 1,000 snakeheads were caught. How does this impact the plan’s success? If there were 1200 snakeheads to begin with, the plan seems to be a success since a significant proportion of snakeheads have been caught. On the other hand, if there were 1,000,000 snakeheads to begin with, the plan seems to be a failure. Thus, an absolute number in isolation without knowing the size of the population does not get us anywhere.

E. Whether rare native fish species in the region face any threats to their survival other than the proliferation of northern snakehead
Incorrect. The goal is to ‘stop the snakeheads from eliminating rare native fish species’. Whether the fish species face other threats does not help us evaluate whether this particular goal will be met. If the goal had been to prevent the elimination of rare native fish species, this option would have made sense.



The goal in this passage was actually divided into two stages.
Officials decided to pay fishers to catch snakehead fish (plan)
→ To keep its population from growing (goal - stage 1)
→ to stop the snakehead from eliminating rare native species (goal - stage 2)

The final goal may not be achieved even if the interim goal is met. The final goal will certainly not be achieved if the interim goal is not met.


SC Notes: “rare native fish species” - this is an example of cumulative adjectives. The two adjectives - rare and native - make sense only in the given order, and no comma is used to separate them. One way to understand this: the adjective ‘rare’ modifies the phrase ‘native fish species’ and not ‘species’ separately. ‘Red fire truck’ is another example of such usage.

Some alternate ways to use multiple single-word modifiers:
tall, beautiful girl: both adjectives modify the noun. In such usage, the two adjectives are separated by a comma.
extremely beautiful girl: the adverb ‘extremely’ modifies the adjective ‘beautiful’ and the adjective ‘beautiful’ modifies the noun ‘girl’.


If you have any doubts regarding any part of this solution, please feel free to ask.
_________________

In my opinion, B and D are the contenders.

I think that D is a useful data to know but since we are asked the MOST useful then probably B is better.

OFFICIAL GUIDE EXPLANATION for answer D confirms this reasoning:

This might be useful for determining whether fishers have been motivated by the plan. This could potentially be useful for determining whether the plan will work; after all, the plan will not likely work if very few northern snakeheads are actually removed. Nevertheless, it is not as useful as noting the changes in the native fish population since the plan first went into effect.

Key is to read the stimulus closely and evaluate the options properly.
With plan, always identify the end goal or most important goal. In difficult stimulus, there might be multiple goals as in this question but important one is to "stop snakes from eliminating rare fish species".

From the stimulus, what we know is that the plan has been in effect for 3 years but we don't know anything about the results. The right option should give us the information that will tell us "whether plan is successful in stopping NS from eliminating rare fish species".

Option (B) and (D) are the major candidates.
So, (D) tells us how many NS have been caught.
- If 0 NS have been caught till now, it tells us that the plan has failed.
- If high number of NS have been caught, it leaves us in ambiguity as we still don't know if plan is successful or failed.


With (B)
- If population is rising or at-least remaining near constant, then the plan has succeeded.
- If population is declining, then plan has failed.

So, the right choice in evaluate the argument should give us certain answers on both the sides.

In essence the argument is:
Snakehead (SH) has no local predators.
PLAN: Wildlife Officials (WO) are trying to keep SH population in check by paying fishers to catch SH.
GOAL: WO hope to stop the SH from eliminating rare native species.

How do we evaluate if this plan is going to make a difference?
1. Is paying the fishers making a difference? i.e. is it reducing the SH's growth?
2. & Is this helping reduce the decline in native fish species?

Let's look at the options now...
A - Irrelevant
B - Looks good. Hold on to this.
C - Wordy and confusing statement. But, on closer inspection, it doesn't talk about the Plan at all. Eliminate.
D - Doesn't tell us what they were before, so we can't evaluate how well the plan is working.
E - Irrelevant