To its admirers, buttery, succulent bluefin tuna has no peer in the sushi world, which may be why those fans do not mind spending as much as $14 for a single bite of it.

But some environmentalists say that passion for bluefin may cause it to be overfished to the brink of extinction. Those people are demanding that sushi restaurants stop serving bluefin in order to save it.

Although dressed in blazers and billowy dresses like any other patrons on a weekend night, the demonstrators, who had reservations, carried fake menus with endangered-species dishes, like “Rack of Mountain Gorilla Seasoned with Powdered Rhino Horn” ($32).

The menus, which were printed in a font similar to that used by Nobu, were meant to be slipped among those used by the wait staff, so servers might unknowingly hand them to diners.