Who ate all the fish? Sudden global fish shortage around 1920.

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The invention nerf for mechanized fishing vessels causes late game shortages.

 

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Before the patch mechanized fishing vessels granted +150% output and -25% RGO size, now it grants +50% output and -25% size.
So the effective supply of fish has been VASTLY decreased.

 

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Not really tested, but my first guess would be +100% output instead of +50%?

 

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Some posts here say is because of a tech that increases output by 50% but decreases fishing wharf size -25%.

To be more exact: The tech did always reduce the RGO size by 25%, but with the latest patch the output benefits were reduced to 1/3 (+150% -> +50%)

Since this causes a huge shortage on the world market, there is not much you can do to overcome it, except for raising your rank or sphering some fish producing nations.