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,

B is incorrect here. It is stated in argument itself the both seals and otters were on decline. So, possibility stated under B ruled out.

Interestingly OA quoted in OG is C, which is debatable.

C could be true in my opinion if the word "inaccessible" is actually replaced by "accessible".

From the rest of the choices E looks attractive as it provides "Additional evidence for decline in seal population" and hence addional support to the agrument that seal population is on decline and hence Orcas will further predate more otters

Whats your take on this?

Vikas

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

why is choice A wrong? you would expect sea urchins, main food of otters, to increase implying that this increase is due to decrease in otters population..

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.

Hello Ashish,

Whats your take on C?

Vikas

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.

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 .

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.

Can someone please explain Answer choice C?

Thanks in advance

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..

Premise: Sea otter population has declined precipitously. Orcas usually feed on seals, but when seals are not available orcas eat sea otters. Seal population declined in 1980's

Conclusion: Orcas are the cause for the decline in sea otter population.

Possible Strengtheners: 1) No other factor was responsible for the decline in sea otter population.
2) Orcas have fed on sea otters resulting in the elimination of sea otter population in that area.

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

B Seals do not eat sea otters, nor do they compete with sea otters for food. - Incorrect - According to the argument the seal population has already declined. Even if they feed on sea otter they are not the immediate cause of sea otter's decline.

C Most of the surviving sea otters live in a bay that is inaccessible to orcas. - Correct - This option states that the sea otter population has dwindled in the area accessible to orcas, strengthening our argument that orcas feed on sea otters if they are accessible.

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

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 - Irrelevant

Answer: 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.
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

I am quiet confused here. I selected last one. reasoning is they are giving a point for validating that seal population is declining cause of fish. so orcas have to eat otters. make sense to me.

C is saying that most of the surviving otters live in bay , inaccessible to orcas. but where is the proof that this situation is due to orcas. this cud be killer whales, sharks ???

How orcas are responsible for this crime ????

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.

I was confused between B and C.
I chose B. My reasoning was that B gets rid of another reason why it should have ONLY been orcas that were responsible.
I let go of C because there could be another reason why surviving otters are in an inaccessible place. Basically, I couldn't find a strong relation here for strengthening. it seemed mildly strengthening. Please help.