Q19 - Each year, an official estimate of the stock of cod

[jardinsouslapluie5]

I don't understand the stimulus.
Could anybody help explaining this?
Thank you.

[mlbrandow]

jardinsouslapluie5,

Every year there number of a certain fish in a body of water is announced. They compute this by taking the average of two independent estimates.--a sampling done by research scientists once a year and the combined reports from commercial fishermen. Usually they match up, but recently the commercial numbers are going up while the research sample is going down.

(C) provides an elegant answer here. The commercial estimate uses the rate that fish are caught. It assumes that if there is a higher rate, then there must be more fish. (C) says, by contrast, that these fishermen simply became more efficient with new technology.

So the rate of fish-catching went up, while the overall number of fish in the area went down. This explains why the research estimate decreased and why the commercial estimate increased over the last 10 years.

Hope this helps!

[zen]

I missed this one but on further blind review got it correct.

So basically, Each year an official estimate of the amount of cod that can be caught by fisherman is computed. This estimate is computed by averaging two separate rates:
1) The amount of cod caught by research vessels during a once-a-year sampling( from here I'm inferring it is not representative of the total of cod caught as this sampling does not last all year; the researchers catch a certain amount and then extrapolate from this sampling of data to estimate the total amount of cod that is available to be caught); and,
2) The average number of tons (we can divide a ton of cod by the average weight of an indivdual cod to arrive at the amount of cod per ton) of cod caught by commercial (non-research) vessels per unit of fishing effort which is defined as 1km of net set in the water for 1 hour( a more simple way of saying this-- it's the average amount of cods in tons(unit of weight) caught by the commercial boats in one hour divided by the number of nets placed...I guess it isn't much simpler :p; sorry!).

So, in previous decades(more than 10 years ago) these two rates usually closely agreed( meaning the two showed similar amounts of cod available to be caught in the water) but in the last decade(the previous ten years) the two rates are not similar. Rate 2 is showing an increase in the amount of cod available based upon increasing amounts of cod being caught, while Rate 1 is has been decreasing. This presents a paradox as it seems that Rate 1 is indicating that the amount of cod is going down, while Rate 2 is showing that more cod are being caught than before despite the findings of Rate 1!

Let's move to the answer choices and find an answer that explains how this can be explained.

A)Does not explain the discrepancy between the rates. If fishing vessels( implying commercial vessels) are exceeding the amount of cod they are legally able to catch, and, are in turn, under-reporting the amount of cod they actually catch, it does not seem likely that Rate 2 would be increasing, if anything, Rate 2 would stay the same or decrease! (this is more than needed but it would be safe to assume that fishing quotas are based on the supply of fish; if the research vessels are reporting less fish available, the commercial vessels would want to under-report to a level at-least equal to Rate 1in order to avoid suspicion; I realize this is wayyy beyond what this question requires).

B)Is irrelevant. The fact that more survey(research) vessels were involved( this implies they would get a more accurate sample) does nothing to explain the discrepancy. If anything, it highlights the discrepancy-- how the hell are the commercial fishing boats getting estimating so much more cod than the survey boats which now have even more accurate samples than before??

D) Does not explain the discrepancy. This questions gives us information about the difference between Rate 1 and Rate 2. But if this has always been the case, as is to be assumed, this does not explain the discrepancy that has arisen in the past ten years! What has changed? This doesn't get to the heart of the problem: what exactly has caused the difference between Rate 1 and Rate 2?

E) Does not help. If fewer commercial vessels are catching the maximum amount of cod because of the over-fishing of cod, how in the past ten years has the amount of cod caught per net over 1km gone up(Rate 2)? It would seem like this average would go down because there is more competition due to less fish due to over-fishing.

Correct answer:

C)This explains the discrepancy. If improvements in fishing technology now allow commercial fishing vessels to catch cod more efficiently and easier then it could be the case that the research vessels' estimates were correct-- the amount of cod is going down. At the same time, this could explain why the commercial vessels' are catching more than before-- they are getting more efficient and better at catching them; so, even though there's less fish, Rate 2 could go up because they are now more effective at catching available fish. Therefore, there's no need for this paradox/discrepancy.

Hope this helps someone someday!