Watt-hours is a measure of energy usage over a period of time; Watts are an instantaneous measure. Your light bulbs, for instance, aren't rated in Watt-hours, just Watts. It's the same for a transducer.

They could have also listed Watt-hours per hour - but that makes no sense.

Your electric bill comes as Kilowatt- hours, as that's the energy that's been metered over the agreed period of time (usually a month).

FWIW batteries are often rated in Watt-hours. That's a measure of the electricity available to be used (look at your UPS, for instance).