Big game fishing uses this technique to cover the area needed a ‘spread’ of lines using the boat’s out riggers is arranged such as in the fig 1.
Sonar won’t exactly help you locate these fish but they can help locate clues and locations that can hold them. That run on the surface so you need a skipper who can read the water and environment e.g. birds.
This is a nice Antigua Fishing Video on the 2011 Fishing Tournament – watch the trolling action from some nice camera angles and submerged work.
Trolling is where lures are dragged behind a boats wake. Billfish such as Marlin hit their quarry with their bills to stun it – doing this to a hookless lure will wrap around the bill as a different way to ‘hook’ the fish. The standard marlin lures will also work that contain hooks for when the marlin goes to swallow the lure and gets hooked.
A single hook is threaded through the nose of this lure typically.