Yes. Thank you for the question.
There are many reasons for this discrepancy. One is the spatial area, so yes, more mackerel might be seen in certain parts of Newfoundland waters, but we're not taking into account what's happening in the rest of the region. Also, we've heard anecdotally that in western Newfoundland, in the Gros Morne area, people are not finding mackerel there. The mackerel distribution can be patchy, and the stock assessment is truly the only way we have to assess the population as a whole.
Another discrepancy is what's called “hyperstability”. Basically, it's what happened with cod: that as abundance of the fish drops, they start schooling more, so they start appearing in certain areas and you see them. They are more abundant in that specific area, but it's not an accurate representation of the whole stock.
Also, there's climate change. We know already that fish are moving further north, so we could be seeing more mackerel at the northern end and fewer mackerel at the southern end.