Eyes on the water: How local mariners can accurately detect a submerged human proxy in shallow nearshore coastal water with modern recreational fish finders.

It has recently been demonstrated that modern recreational fish finders with high-frequency (800 kHz) Sidescan transducers can detect submerged human bodies. This ubiquitous technology is widely used on the water and has the potential to be utilized for the rapid detection of submerged decedents in any waterbody. This research investigates whether, with minimal training, the boating public can use modern recreational fish finders to accurately locate a submerged human proxy in a shallow nearshore coastal location. One human-shaped plastic proxy was submerged, resting on the water bottom, at a depth of ~8 m in a semi-sheltered bay with a silty bottom. Ten parallel searches were completed by nine local volunteers using four different recreational vessels. Volunteers reported the location of the proxy when seen on the fish finder. Three vessels were equipped with recreational fish finders capable of high-frequency (800 kHz) Sidescan and Downscan sonar. One vessel was equipped with low-frequency (200 kHz) conventional down-looking sonar. High-frequency Sidescan sonar provided clear and distinctive visuals of the submerged proxy in all volunteer sonograms. Most reported locations were <10 m of the target location. This research demonstrated that local mariners with mixed boating experience can successfully use recreational fish finders with high-frequency (800 kHz) Sidescan transducers to identify and report accurate locations of a submerged human proxy in a shallow (<20 m), nearshore coastal environment. This sophisticated recreational technology provides the potential to enhance community awareness and involvement for the early detection of submerged decedents.