Today coastal countries own the surrounding marine waters stretching 200 nautical miles from their shoreline in terms of exclusive rights of exploiting its resources (their exclusive economic zone (EEZ)).
The previous limits of 3 and later 12 nautical miles (nm) are said to resemble the range of a cannon shot and therefore may have been established because of strategic reasons.
Iceland extended its EEZ to 200 nm during the cod wars to secure and be able to defend fishing rights against the British. Chile and Peru already claimed in 1947 EEZs of 200 nm but I'm not aware of the reasoning.
I have not much doubt that, unlike the case with Iceland, the main motivation behind establishing large EEZs is to extend territories out of strategic reasons and to secure marine resources (especially energy resources).
But, are there other cases where reasons of seemingly minor importance (well, fishing was certainly so much of importance to Iceland to have a big quarrel with the British) were the motivation of countries to extend their EEZ beyond the previous limits of 12 nm? What was the reasoning of Chile and Peru? I'm especially interested in cases where fishing was found to be the single most important factor.