Each year, an official estimate of the stock of cod in the Grand Banks is announced.
Statements
Two different methods for estimating how many cod (a type of fish) are in the Grand Banks.
Method 1 (sample-based) Once a year, research vessels go out and sample the area.
Method 2 (commercial tonnage) Throughout the year, commercial vessels go fishing and they record the number of tons of caught caught per km of net per hour.
In the past these two estimates were very similar.
pivot (However) For the last decade, the number of fish according to Method 2 is higher and the number according to Method 1 is lower.
Evaluate
Because of that big Pivot word, however, announcing the final sentence, we get the sense that our thinking job is to Reconcile the Pivot.
What does it suggest to us, given that Method 2 is rising and Method 1 is shrinking.
For method 2 to rise, it means that commercial vessels are catching more tons of cod per hour per km of net set out in the water. That could be due to there being more fish in the area, better knowledge of where to find the existing fish, better nets, etc.
However, it's pretty hard for us to fathom that there are more cod in the area, given that Method 1's number has been going down.
The once-yearly research vessel might be catching less cod because there are just less cod in the water, because the researchers got worse at catching cod, or because they changed what time of year they go surveying?
Goal
All of these possible explanation seem very speculative. They definitely aren't Must Be True inferences, but this question seems primed to make us try to Solve the Causal Mystery, so we may end up picking the most supportable hypothesis.
It seems unlikely that more cod / less cod would be an answer, since either direction would help explain one Method but make the other Method's result even more surprising.
The only thing I can think of that can explain both is if the commercial vessels got better at catching cod (causing their estimate to go up) and by catching more cod they emptied out the water so that when the researchers roll in and do their measurement, it comes out lower than before.
That would potentially explain why commercial tonnage is increasing by about the same amount as the sample-based is decreasing.