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Researchers in South Australia estimate changes in shark [#permalink]
14 Jul 2010, 13:42
36% (02:48) correct
64% (01:51) wrong based on 39 sessions
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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.
I go for C. There is another reason that is threat to the population of shark, which is the "unaware" action of fishing. Thus, we will understate the population of shark if we just use the CPUE to estimate the level of population.
I went for C using a similar reasoning to dungtd's.
In my opinion, if E is true, the shark-fishing boats would be getting more sharks, elevating CPUE.
What am I missing?
After rereading and rethink about it...
The conclusion establishes a relationship between CPUE and total population of sharks.
If sharks can be detected with greater accuracy, CPUE can remain constant, even tough the total population is decreasing. Hence, E weakens the conclusion.
I think that problem with C is that this "incidental mortality" would happened all the time, before or after 1973, not affecting CPUE and/or total population.
Am I right now?
Yes you are. I like your reasoning. Just wanted to note that the "incidental mortality" would not affect CPUE but it definitely will affect total population. Unless you use it as a percentage comparing before and after 1973. In that case, the researchers would know that they need to deduct the incidental mortality from the CPUE measurements.
I still dont understand how E weakens the conclusion. Can someone please explain this.
Let me try to explain it according to my point of view:
The conclusion says: if CPUE remains constant, the total population of sharks must be also "constant" (or, in other words, it didn't change during the period from 1973 to current time).
IMHO, answer E weakens the conclusion because it present a more efficient way to find sharks. Taking this in consideration, we can assume that shark-fishing boats are able to catch the same amount of sharks (CPUE constant), even if total population of sharks is smaller than before 1973. Therefore, answer E presents an argument that "breaks" the conclusion CPUE constant = Total population constant.
since 1973 the CPUE for a particular species of shark has remained fairly constant(premise). given this it can be concluded that population of sharks in the waters around South Australia must be at approximately its 1973 level. the argument states that.
But will the shark population remain constant at 1973 level ??given that since 1980 commercial shark-fishing boats have used sophisticated electronic equipment that enables them to locate sharks with greater accuracy.
E is a detracting piece of evidence..whn introduced will weaken the con
Conclusion: Because the catch (CPUE) is constant so the shark population is not dwindling. This is causal statement.
This can be destroyed if there is a third factor "dwindling" the population. "sophisticated EE" are Third factor (alternative explanation) (E) Since 1980 commercial shark-fishing boats have used sophisticated electronic equipment that enables them to locate sharks with greater accuracy.