Probably around 82%. I imagine grocery store sushi has more in common with the rest of grocery store fish than it does with sushi shop sushi. The grocery store probably buys the fish for both from the same chain of suppliers.
I'm less convinced - sushi outside of a restaurant context, from the similarity in presentation style and selection in the DC area at least, seems to be outsourced to daily deliveries from regional suppliers
Hmm, I wasn't aware of that, I thought they usually just had the butcher or somebody throw it together in house. That was just a guess though.
well it's sold in the butcher/fresh fish section of the store, so I'm pretty sure it's prepared on site using whatever is used to supply their normal tuna. at least I hope.