Which flippers do sea lions primarily use for underwater thrust, enabling them to "fly"?

Answer

Relatively larger, more paddle-like front flippers

Sea lions primarily use their powerful, larger front flippers for underwater thrust, effectively 'flying' through the water while keeping their rear flippers mostly for steering.

Which flippers do sea lions primarily use for underwater thrust, enabling them to "fly"?
mammalPinnipedsea lionFur Seal