(Seafood Business) Toward the end of the 2011 documentary “Jiro Dreams of Sushi,” the chefs at Tokyo’s renowned sushi restaurant Sukiyabashi Jiro discuss the future of the oceans that supply their colorful and coveted bite-sized creations. With a furrowed brow, Yoshikazu Ono, son of the legendary Jiro Ono, is particularly concerned about bluefin tuna, known in Japan as honmaguro. The quintessential sushi morsel, o-toro (fatty tuna), comes from the belly of the bluefin.More