The boat on the stern ramp is used to deploy a large purse seine net, which is usually used to catch Tuna Fish. Basically, once a school of tuna has been identified. The boat is launched with one end of the net. The other end remains with the mother ship. The small boat then takes the net and encircles the school of tuna, and passes it back to the mother ship. Thus trapping the school of tuna, which is then hauled on board the mother ship. As far as I know the method and style of these vessels is pretty much the same, wherever tuna is found.