Between 1980 and 2000 the sea otter population of the Aleutian Islands

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument‘?

(A) The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

(B) Seals do not eat sea otters, nor do they compete with sea otters for food.

(C) Most of the surviving sea otters live in a bay that is inaccessible to orcas.

(D) The population of orcas in the Aleutian Islands has declined since the 1980s.

(E) An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.


Let’s look at the stimulus-

Premises- Between 1980 and 2000 the sea otter population of the Aleutian Islands declined steeply.
There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators.
Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s.

Conclusion- Therefore, orcas were most likely the immediate cause of the otter population decline.


(A) The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.
We have to strengthen the conclusion that orcas were the cause of sea otter population decline. Option A talks about the population of sea urchins. Irrelevant. Eliminate.

(B) Seals do not eat sea otters, nor do they compete with sea otters for food.
What seals eat is not relevant to the argument. Eliminate.

(C) Most of the surviving sea otters live in a bay that is inaccessible to orcas.
Correct. Option C says that most of the surviving otters live in a bay that is inaccessible to orcas. This is probably the reason why otters are still surviving there. C strengthens the conclusion that otters were most likely the immediate cause of the otter population decline.


(D) The population of orcas in the Aleutian Islands has declined since the 1980s.
Weakens the argument. If orcas were responsible for the decline in the population of sea otters, a decline in the population of orcas should have led to an increase in the population of sea otters. Eliminate.

(E) An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.
What seals used for food is irrelevant to the argument. Eliminate.

VP
GMAT Verbal SME

Hello Vikas,

I can try to give a reasonable explanation, though I am not too good at it

The argument says that the otter population has declined. It also says that malnutrition and disease were not the reasons, so we rule these causes out.
The argument later says that maybe orcas were responsible for this decline in otter population by providing evidence that Orcas did so because of an acute shortage of seals, the primary food of orcas.

The conclusion states that probably orcas were the sole reason for decline in otter population.

Since we have to strengthen this conclusion, we have to somehow prove that orcas are the real culprits and not something or someone else.

As per statement C, Most of the surviving sea otters live in a bay that is inaccessible to orcas.
If otters are surviving in the bay, then this rules out any other possibility for the cause of decline in otter population.
Now what strengthens this argument is the fact that this bay is inaccessible to orcas and this prevents them from hunting the otters, therefore the remaining otters survive in the bay. All the other otters who were accessible to the orcas were hunted down and this is the reason for the decline in otter population.

Hope I have managed to be convincing in my reasoning.

We need to strengthen the argument i.e. strengthen the conclusion.
The conclusion is that Orcas are probably the reason for decline in otter population.

It may be true that a decline in otter population (Cause) is the reason for abundant growth of Urchins (Effect)
but you cannot validate the reverse reasoning that since there is an abundant growth of urchins it is solely because of decline in otter population. There maybe other reasons for increase in urchin growth + the extra knowledge of sea urchins doesn't show how orcas are responsible for decline in otter population.

Orcas hunt Otters-------------> Decline in otter population -------------> Increase in sea urchin population .................... (May be true but there is nothing to validate this)

There should be some more evidence provided in option A to prove the reverse reasoning true.

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument?

A) The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.
WRONG:- Irrelevant:- Of course the population of sea urchin will increase, if there is no otter to eat them. But this is not strengthening. This is just an implication.

B) Seals do not eat sea otters, nor do they compete with sea otters for food.
HOLD IT -So, Seals did not killed otters. OK !! But this is not directly strengthening that Orca's (which are whales by the way !) killed otter. LET IT GO !! WRONG

C) Most of the surviving sea otters live in a bay that is inaccessible to orcas.
RIGHT:- Only those otters survived that lived in area accessible to orcas. Therefore Orcas must be definitely responsible for killing otters.

D) The population of orcas in the Aleutian Islands has declined since the 1980s.
WRONG:- Irrelevant :- Useless information

E) An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.
WRONG:- The food decreased slightly. BUT otter died in large numbers. (FROM ARGUMENT:-the sea otter population of the Aleutian Islands declined precipitously) so lack of food cannot be the reason. (FROM ARGUMENT:-There was no signs of malnutrition). Meaning lack of food was not the cause.

C IS THE ANSWER

E cannot be the answer simply because we are told that Orcas are "probably" the reason for decline in otter population.

Even if there had been a slight decline in fish population, it is not sufficient to show how it affected the seal population to such an extent that seal population was greatly reduced and that this caused orcas to hunt otters. There are several assumptions to be made to prove this hypothesis right.

Guess it clears some doubts

In option B:
I think option B makes more sense because if the seals did eat the otters then the argument that orcas were the reason for the decline of the otters does not hold true.
The seals could also have been responsible for the decline of the otter population.
(They have mentioned that the seal population declined dramatically, so there were still a few seals left)

I thought in the same lines initially.Either it should be B or C. i opted for B. We both missed a logic. Say If Seals eat otters. From the argument we know that seal population decreased. So we have to see an increase in otter population, Assuming that Orcas don't eat extra. But we haven't seen any increase in otter population. So this option B is wrong. That leaves us with option C.

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument‘?

A The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

B. Seals do not eat sea otters, nor do they compete with sea otters for food.

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas.

D. The population of orcas in the Aleutian Islands has declined since the 1980s.

E An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.


Premises 1--Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously.
premises 2 --There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators.
premises 3-- Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s.

conclusion---- Therefore, orcas were most likely the immediate cause of the otter population decline.



Otter 's main food is sea urchins
orcas normal prey is seal
seal prey is fish

A The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

It says main food of the sea otters is sea urchins has increased because sea otters population declined . Now as per premises 3 Orcas will eat otters when seals are UNAVAILABLE ----UNAVAILABLE means not available completely that is not the case here because as per 2nd statement of the premise 3 says that seal population declined dramatically not UNAVAILABLE . It means that though orcas food may decrease but still available that means may or may be orcas attacked Otters .


B. Seals do not eat sea otters, nor do they compete with sea otters for food.


irrelevant

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas.


This strengthen the statement because most sea otters survive because orcas was not able to reach sea otters. hence those sea otters couldn't survive was those preyed by orcas

D. The population of orcas in the Aleutian Islands has declined since the 1980s.

irrelevant
E An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.

Fishing does slight decline of the fish that is the prey of seal . It means seal is available for prey to Orcas. as per premise 3 Orcas will eat otters when seals, their normal prey, are unavailable, , which is not the case here .

Hi,
I'll help you with that..

lets rephrase the para..

1. in some period of 20 years, the number of 'sea otters' declined drastically.
2. No disease or food shortage was not there and hence has not been attributed to the decline.
3. Orcas will eat otters when seals, their normal prey, are unavailable,
4. starting of this period was the time when seals population declined.
5. from 4 above ,we can say that Orcas ate otters

now from choices, we have to look for a strengthener..
lets see the answer C..
Most of the surviving sea otters live in a bay that is inaccessible to orcas..
this tells us that the only ones which are surviving are in a bay , where the Orcas are unable to reach..
so it strengthens the conlclusion that indeed Orcas fed on the otters which were in accessible areas..

Hello,

IMHO (B) doesn't help get rid of alternative reason(s) for decline of sea otters population, because 2 situations "Seals DO eat sea otters" and "seals DO compete with sea otters for food" cannot be the reason why sea otters population is reduced. Why? Let's look back at stimulus. It is mentioned that "seal population declined dramatically", so if seals actually eat and compete with sea otters for food, then the decrease in seals number will result in increase in sea otter number. This totally contrasts with premise.
That's why (B) is not correct.

Hope this helps.

(C) tells us that some otters were still surviving as of the year 2000, while some were not.

In addition, it gives us some information about those surviving otters: most of them live in bays that are inaccessible to orcas.

This certainly doesn't prove that the orcas killed off the otters living in more accessible areas -- but it does support that conclusion. Otters in orca-infested waters died off, while otters in orca-free waters survived.

Our job is just to strengthen the argument, not to prove that it is 100% ironclad. (C) does exactly that, and none of the other answer choices come close, so (C) is the correct answer.

I hope that helps!

Here's the relevant information from the passage:

• Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously.
• the Aleutian Islands seal population declined dramatically in the 1980s.
• Orcas will eat otters when seals, their normal prey, are unavailable
• Therefore, orcas were most likely the immediate cause of the otter population decline.

What does (B) add to this chain of logic?

On the surface, this looks promising! If seals do not eat sea otters, then perhaps it strengthens the argument that the orcas are to blame.

However, this doesn't hold up to closer analysis of the information in the passage. The seal population "declined dramatically in the 1980s." We are concerned about the decline of the sea otter population "between 1980 and 2000."

If the seals caused the sea otter decline, then it makes no sense that the otters continued to dwindle for at least a decade after the seal population collapsed. In fact, if the seals were the issue, we would expect the sea otter population to increase if the seal population decreased. That's not what happened, so just from the information in the passage we can be confident that the seals are not the problem.

Receiving further confirmation of this in (B) doesn't really strengthen the author's argument. (C), on the other hand, provides additional information that points to orcas as the immediate cause of the otter population decline. (B) is out and (C) is the correct answer.

I hope that helps!

Conclusion: Orcas were primarily responsible for the decrease in sea otter population.

We have to strengthen the conclusion.

According to E: An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food. --> Here you are trying to establish that orcas consumed sea otters because the population of seals reduced. But this is already stated in the argument and we are strengthening the stated facts. Moreover, we know that the number of fishes reduced but did the number reduce so drastically that the seals could not feed on them anymore. We also have no information available to infer that the seals did not consume any other organism to survive. For the stated reasons, this option can easily be eliminated.

Option C: Most of the surviving sea otters live in a bay that is inaccessible to orcas. --> Presents evidence in support of the conclusion by stating that if there are no orcas the sea otters thrive.

Hope it helps.

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument‘?

A. The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined. - Incorrect: Out of scope

B. Seals do not eat sea otters, nor do they compete with sea otters for food. - Incorrect: Shell game

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas. - Correct: When Cause does not happen [Orcas], Effect does not happen [Otters do not diminishl]

D. The population of orcas in the Aleutian Islands has declined since the 1980s. Incorrect: Out of scope

E. An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food. - Incorrect: Out of scope

Think of the food chain: Orcas on top. They eat Seals. When seals are not available, they eat sea otters.

The argument tells us that seal population has declined. From this, we are concluding that orcas are eating otters. Now, what seals are eating is kind of pointless, right? Anyway, their population is declining. If we were worrying about increasing population of another species, we would have been interested in what seals are eating. But what we are interested in is the decreasing population of another species. This species acts as an alternate to seals as prey. Hence, the relation we are focusing on is orcas to seals/otters.

I wouldn't think so. Even if seals were eating otters, this would just tell us that the population of otters is less affected by seals now. But it would not strengthen that orcas are the ones reducing otter population. We need to find the reason for reduction in otter population.