In our commercial salmon troller, virtually identical to the picture, we had a 3-71 series Detroit (screaming Jimmy) 2 stroke diesel. IIRC it had a "flapper plate", operated by a cable that closed off the intake tract to stop the engine. I don't remember any fuel shut off valve? If I had another diesel I would try to fabricate something similar to be able to stop the engine without being "up close and personal" with it.
Detroit Diesel Series 71 - Wikipedia, the free encyclopedia
This reminded me of an incident my Dad and watched many years ago. We kept our boat at the San Francisco Fisherman's Wharf which was mainly other commercial boats and some charter fishing boats, aka "party boats" or the "puker" fleet". There were no floats, just a series of pilings to tie up to.
One of the party boat skippers was a real cowboy, always coming in way too fast and at the last second dump it into reverse and give it full throttle. Very impressive, good show, old boy. One day he couldn't get it into reverse, slammed the bulkhead and then proceeded to ricochet the boat all over the basin then hitting a boat two spots from us with an awful crunching noise, very bad.
Apparently he had no way to shut down the engine from the helm and his throttle and shift cables didn't work.