I'm not sure what you are seeing when you are overlaying those maps, but I am seeing a clear overlap between the western extent of the pacific garbage patch, an

I'm not sure what you are seeing when you are overlaying those maps, but I am seeing a clear overlap between the western extent of the pacific garbage patch, and fishing activity. Besides that, you are conflating "where fish are fished" with "where fish live/grow up". Many fished species (and/or their prey) heavily migrate, and when migrating take advantage of the same ocean currents that lead to formation of the garbage patch, and are thus in close proximity. Of course the majority of fishing activity will be close to land, as that's more economical, but that doesn't mean that the fish fished there have only grown up their and/or not been exposed through to plastic via their food chain.