Eek, don't think they are, no. They use mayo and stuff in them.
Here's some of them; (syns are in order of EE, Red, Green)
Tesco, Sushi Pack, California Rolls, chilled, 203g pack 4½ 11½ 4½
Tesco, Sushi Snack Selection, chilled, 98g pack 1½ 5 1½
Tesco, Sushi Box, Veggie, chilled, 147g pack 1 9 1
Tesco, Prawn, Tuna & Vegetable Sushi Box, chilled, 142g pack 1½ 8½ 1½
Tesco, Fish Sushi Box, Small, chilled, 149g pack 2½ 10 2½
Tesco, Mini Fish Sushi Box, chilled, 100g pack ½ 5½ ½
Tesco, Medium Fish Sushi Box, chilled, 222g pack 4½ 11 4½
Tesco, Vegetarian Sushi Pack, chilled, 157g pack 1 10½ 1
Tesco, Salmon & Veg Snack Sushi Box, chilled, 142g pack 1 7 1
Tesco, Salmon Snack Sushi Box, chilled, 103g pack 1½ 5½ 1½
Tesco, Fish & Vegetable Medium Sushi Box, chilled, 240g pack 3½ 15 3½
Tesco, Large Fish Sushi Box, chilled, 284g pack 6½ 15½ 6½
Tesco, Chicken Sushi, chilled, 147g pack 2½ 9½ 2½
Tesco, Fish & Vegetable Sushi Box, chilled, 151g pack 1½ 7 1½
Marks & Spencer, Vegetarian Sushi, chilled, 158g pack 1 9 1
Marks & Spencer, Medium Fish Sushi Selection, chilled, 189g pack 3½ 11½ 3½
Marks & Spencer, Eat Well Sushi, chilled, 96g pack ½ 5 ½
Waitrose, Taiko Sushi, chilled, 262g pack 6½ 13 6½
Marks & Spencer, Californian Sushi Roll Selection, chilled, 225g pack 4½ 12 4½
Marks & Spencer, Large Fish & Vegetable Sushi, chilled, 320g pack 11 15 11
So they aren't massive syns (apart from the M&S ones) but you do need to count them.