Each year, an official estimate of the stock of cod in the Grand Banks is announced. This estimate is obtained by averaging two separate estimates of how many cod are available, one based on the number of cod caught by research vessels during a once-yearly sampling of the area and the other on the average number of tons of cod caught by various commercial vessels per unit of fishing effort expended there in the past year—a unit of fishing effort being one kilometer of net set out in the water for one hour. In previous decades, the two estimates usually agreed closely. However, for the last decade the estimate based on commercial tonnage has been increasing markedly, by about the same amount as the sampling-based estimate has been decreasing.

Which one of the following, if true, most helps to account for the growing discrepancy between the estimate based on commercial tonnage and the research-based estimate?
(A) Fishing vessels often exceed their fishing quotas for cod and therefore often underreport the number of tons of cod that they catch.
(B) More survey vessels are now involved in the yearly sampling effort than were involved 10 years ago.
(C) Improvements in technology over the last 10 years have allowed commercial fishing vessels to locate and catch large schools of cod more easily.
(D) Survey vessels count only those cod caught during a 30-day survey period, whereas commercial dishing vessels report all cod caught during the course of a year.
(E) Because of past overfishing of cod, fewer fishing vessels now catch the maximum tonnage of cod each vessel is allowed by law to catch.

(D)

If survey vessels count only 30-day survey period and commercial fishing vessels report for the whole of a year, there will be discrepancy in numbers..

I would go with C here.

D is a trap, since this has always been the case and the discrepency has only recently made an appearence...

If however, the fishing companies can locate fish easier, they can fish out a larger precentage of fish, pushing down the actual number of available fish, while (seemingly) increase their catch...after several more years, their yield will begin to fall...but new technology makes sense of the current paradox.

I will go with D

The decoy I see in C is that it only speaks about the commercial vessels. For all I know the same could be held for Sampling vessel too. They too could use the best technology possible. However choice D clearly presents the fact from both the perspectives.

Hey guys,

A challenger to those who answered C or D!

I would go with A!!!

(I thought hard between A and C but decided to go with A)

If fishing vessels often exceed their fishing quotas, then there would be fewer fish remaining for the survey vessels to report. There is an inverse relationship as mentioned in the passage ("However, for the last decade the estimate based on commercial tonnage has been increasing markedly, by about the same amount as the sampling-based estimate has been decreasing.") and fishing vessels catching more and thus leaving less for survey vessels to report explains it.

A weakness here though, is that the fishing vessels can continue to underreport the same amount and thus their estimate based on commercial tonnage can stay the same...

(D, I agree appears to be a trap...)

One and only (C)
_________________

"Education is what remains when one has forgotten everything he learned in school."

I also go with C as it explains why the discrepancy is in the estimate and commercial tonnage is happening now. Because of advanced technology commercial fishing vessels can catch more cod, than the survey vessels. D cannot explain why the discrepancy happens now, because earlier there were better agreement between these two methods

C.