One of the favourite tricks of anti-salmon farming activists is to take a graph showing how wild salmon returns have declined in the past few decades, and compare this line to the increase in the number of salmon farms on B.C.’s coast in the same time period.
This falls firmly into the “correlation does not equal causation” category but this sort of comparison looks compelling, because our human brains are hard-wired to see patterns and connections, even when there actually aren’t any (see our “Korean Fan Death” post for more on this).
This sort of comparison is not helpful because as we have said before, salmon have been in decline all over the Pacific coast since the 1980s, in places where there are fish farms and in places where there are no fish farms. Obviously such a broad trend is indicative of something big and cannot be blamed on just one thing, i.e. salmon farms in one area of the coast.
That said, we can make graphs too (or at least re-link them). If correlation is causation in your mind, consider this graph before you blame salmon farms for the decline of B.C. salmon returns.