@bathsheba,
Boat is one of his work horses used mainly for tuna farming, you can see some of the air-cylinders on the deck used by the divers, when they descend into the tuna farms for inspecting the fish and the nets.
Some predators like, sharks, seals and dolphins have a habit of invading the farms and they have to be removed. That TV documentary 'Tuna Cowboys" will show you what I mean.
I have a video here and a series of photo's taken some years ago when they had a shark in their farm which made headlines all over the Country. The monster was nearly 18 feet in length, a diver had to enter the farm and shoot the beast with one shot. If I can find the photo's I'll post one. Anyway, the aftermath was, the Government brought in Legislation and made "The Great White Shark" a protected species!!
When we go fishing I'm the one using the downrigger, son doesn't need one, he just uses a handline and hauls them in quicker than I can! I suppose experience does that, his fingers feels when a fish is nibbling his bait, one jerk and another bites the dust.
You're right this has turned into a fishing thread.