Hi Calli
Jackie is right, there are very few reeors in your composition. (and several in mine, that was supposed to say few errors) I would use "in the sea" rather than "at sea" since the latter usually refers to someone/something temporarily on the ocean -"John the sailor is away at sea". It also used to mean someone who is very confused - "The new receptionist is all at sea."
I liked the mental picture of "affluent fish" with pearl necklaces and little tiny mink jackets but "an abundance of" or "a richness of" is accurate.
we can have the fishing industry develop at a rational scale I would have said "at a rational pace" or "in a rational manner" since scale refers to a comparison of relative sizes eg comparing 1cm on a map to 1km in a country. and there is no specific comparison given. It does make a good pun since fish are covered with scales but don't tell Faldage I suggested it. You could say "at a scale appropriate to the number of fish" but that would sound awkward.
Jackie was also right about boats -relatively small- vs ships -large. Vessels is correct for all sizes but is usually used for large ships or for the plural especially when there are more than one size of vessel.
All in all, well done.