It is in the news (paper, writeup) that a study has just come out that some seafood, particularly small wild pelagics such as mackerel, herring and pilchard (eg. Japanese pilchard = 0.498 kg CO2e per kg), have a far smaller green house gas emissions than meat (eg. beef = 56 kg CO2e per kg), and comparing the figures to other datasources lower even than vegan protein sources, eg. soya at 6.44 kg CO2e per kg.
Does this actually mean that a small wild pelagic fish based diet is sustainable, or do other factors (such as the recent work on plastic polution) mean that the environmental harm is actually greater than more traditional "green" foods?
Nutrient density scores are based on the 21 nutrients common to all species (full bars) and, where possible, 23 nutrients (grey lines) (for nutrients see Methods). GHG emissions of individual seafood species are representative of the dominant production method for each (or weighted if multiple major production method is employed globally). Solid bars indicate species from fisheries, and striped bars species from aquaculture. Comparisons to land-based animal proteins are based on nutritional content of averaged meat cuts for beef and pork, and fillets for chicken. GHG emissions of beef are beyond the scale at 56 kg CO2e per kg edible product.