Bunuel wrote:
Researchers in South Australia estimate changes in shark populations inhabiting local waters by monitoring what is termed the “catch per unit effort” (CPUE). The CPUE for any species of shark is the number of those sharks that commercial shark-fishing boats catch per hour for each kilometer of gill net set out in the water. Since 1973 the CPUE for a particular species of shark has remained fairly constant. Therefore, the population of that species in the waters around South Australia must be at approximately its 1973 level.
Which one of the following, if true, most seriously weakens the argument?
(A) The waters around South Australia are the only area in the world where that particular species of shark is found.
(B) The sharks that are the most profitable to catch are those that tend to remain in the same area of ocean year after year and not migrate far from where they were born.
(C) A significant threat to shark populations, in addition to commercial shark fishing, is “incidental mortality” that results from catching sharks in nets intended for other fish.
(D) Most of the quotas designed to protect shark populations limit the tonnage of sharks that can be taken and not the number of individual sharks.
(E) Since 1980 commercial shark-fishing boats have used sophisticated electronic equipment that enables them to locate sharks with greater accuracy.
So CPUE is (Number of sharks) /( Hour * Kilometer) Now since 1973 CPUE has remained constant. Passage assumes
THE NUMBER of sharks or the Population of Sharks has remained constant. We are asked to weaken the Argument.
Let CPUE in 1973 be 12/4 = 3So we have to prove that the Population ( Number of Sharks ) has NOT remained constant, yet CPUE has somehow remained constant. How can we do this? There are two ways we can keep the CPUE constant yet vary the population:
a) We can
INCREASE the Numerator (Population) and increase accordingly the Denominator ( time and Distance of net ) hence this is one way, we could keep CPUE constant, yet
NOT keep the population constant. This could weaken the Argument.
e.g.15/5=3b) We can
DECREASE the Numerator (Population) and decrease accordingly the Denominator ( time and Distance of net ) hence this is another way, we could keep CPUE constant, yet
NOT keep the population constant. This could weaken the Argument too.
e.g.6/2=3Let's see the options:
(A) Does not relate any way to the numerator or Denominator, cannot help to weaken the Argument -
INCORRECT.(B) Does NOT help to weaken either, in an INDIRECT way says population has in fact remained constant, because no migration has taken place.
INCORRECT.
(C) Talks about another cause by which Shark population is affected,but does not help to address whether population has actually increased or decreased. Irrelevant.
INCORRECT. (D) Not in line with our pre- thinking, does not help to weaken the Argument. Irrelevant.
INCORRECT.(E) This tells us that Sophisticated electronic equipment, helps to locate shark with greater accuracy, so now no need to set huge gill net in miles of water. Since we know where the shark is , we can directly cast our net in that area. This will certainly help to reduce our net distance and hence our denominator, so there could be less sharks ( less population ) and we are catching them with less miles of net, because of our sophisticated equipment. This is keeping the CPUE constant. Hence this option definitely helps to weaken the argument.
CORRECT.Ans- E
Hope it's clear.