The Good Fish Guide’s ratings are based on various factors — including the environmental impact of the fishing activity, the influence this has on other marine life and volumes of bycatch. It should be noted that individual ratings do not refer to a particular seafood species, but that of a species caught or farmed by a particular fishery. According to the Marine Conservation Society, 14 ratings have recently been downgraded to the “Fish to Avoid” list — including monkfish from the North Sea and west of Scotland, some sources of crab and lobster, and many species of skates and rays.