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.
18. If the statements in the passage are true, which one of the following is most strongly supported by them?
(A) Last year's official estimate was probably not much different from the official estimate ten years ago
(B) The number of commercial vessels fishing for cod in the Grand Banks has increased substantially over the past decade
(C) The sampling-based estimate is more accurate than the estimate based on commercial tonnage in that the data on which it relies is less likely to be inaccurate
(D) The once-yearly sampling by research vessels should be used as the sole basis for arriving at the official estimate of the stock of cod
(E) Twenty years ago, the overall stock of cod in the Grand Banks was officially estimated to be much larger than it is estimated to be today
19. 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
18. A is the answer - both estimates have strayed in opposite directions at the same rate - thus, zero net change on the official estimate.
C is a trap answer - would be correct if the question was asking for a possible explanation for the discrepancy between the two estimates.
19. C best explanation for the discrepency between research and commercial fishing vessels.