A guilt-free guide to eating from our oceans is provided on Casson Trenor's blog, Sustainable Sushi (sustainablesushi.net).
I'm still coming to grips with the concept of eating only types of seafood that exist in sustainable numbers and that are only caught using methods that don't harm other creatures. I know, for example, I shouldn't touch bluefin tuna- but I confess I do eat it once in a while.
The blog doesn't make me feel much better about some of my other choices at the sushi counter. Who would have thought that unagi (above right; freshwater eel) is so bad for the environment? Much of it is raised on farms that release waste into surrounding waters and domesticated eels escape and breed with wild varieties. They're also raised on 'fish meal'; researchers estimate 2.5 tonnes of wild fish are needed to produce one tonne of marketable eel.
Another favourite, ankimo (right; monkfish liver), isn't much better- it's harvested using destructive bottom trawling, a method also used to catch wild shrimp and certain types of flatfish. Seafood that gets Trenor's stamp of approval includes cuttlefish, farmed oysters (he says wild oysters are often harvested by dredging the ocean floor) and certain types of snapper.
Trenor, who works for Greenpeace, has also written a book, Sustainable Sushi: A Guide to Saving the Oceans One Bite at a Time.