Fishing for the missing: The application of recreational fish finders for underwater body detection in shallow waters

Early detection of submerged bodies is essential to increase the possibility of recovery. Different water bodies present different challenges, particularly rivers and the ocean, where chances of detection are vastly reduced. Modern recreational fish finders incorporate multiple sonar technologies, including Sidescan sonar, at high-frequency resolutions, similar to commercial units. Recreational units are widely available and usually hull-mounted, allowing them to be utilized on almost any vessel in shallow and difficult to navigate environments. Recreational fish finders are currently an untapped resource which may assist search teams with the early detection and recovery of human remains submerged in shallow water (<20 m). This research investigated the efficacy of a modern recreational fish finder attached to a kayak to detect human proxies and living human volunteers submerged at shallow depths in (1) two indoor freshwater environments and (2) two outdoor environments (a freshwater lake and a nearshore coastal environment). Results demonstrated that recreational fish finders can detect human bodies submerged in both fresh and saltwater contexts at shallow depths within the water column and on the water bottom. Recreational units equipped with Sidescan sonar (800 kHz) provided the necessary resolution for underwater body detection at shallow depths. These sophisticated sensors are currently used by recreational boaters and anglers, and offer the opportunity to increase the eyes in the water not just by search and recovery teams, but by the public itself.