Development of an Underwater Infrared Camera to Detect Manatees (2005)

In calendar year 2004, watercraft related mortality was the second leading cause of death of the Florida manatee (Trichechus manatus latirostris) accounting for 25% of total known manatee deaths. In an attempt to reduce this significant cause of manatee mortality, the Florida Fish and Wildlife Research Institute has instituted two rounds of Manatee Avoidance Technology grants. Herein I report the results of an evaluation of the ability of underwater infrared video cameras to detect captive manatees and other non-living targets. If such cameras could detect manatees at sufficient distances, they could be mounted in the bows of watercraft and the resultant images could be projected at the helm of the vessel, enabling the vessel operator to reduce speed, take evasive action, or both. Two types of cameras were examined: 1) A SeaView underwater video camera system from PowerLinx, St. Petersburg, FL, and 2) An Atlantis underwater camera system (AUW-535C) from JJC Communications, Inc., Englewood, NJ. Preliminary investigations of the ability of these cameras to detect small objects indicated that their resolution decreased with distance from the target and depth, with the highest resolution closest to the target and near the surface. However, even at optimal depth, the maximum detection distance for the small target with the SeaView Camera was less than 3 m, and less than 5.5 m for the Atlantis camera. Thus, the Atlantis camera was marginally better able to detect the small target than was the SeaView camera. The cameras were then tested on a plywood silhouette of a manatee placed vertically in the water. In this case the detection distance increased with depth, being greatest at a depth of 2 m, but in no case was the detection distance greater than 5 m. As before, the Atlantis camera was marginally better able to detect the plywood manatee silhouette than was the SeaView camera. The cameras were then tested using living captive manatees at the Lowry Park Zoo (LPZ). Due to the clarity of the water at LPZ, manatees were visualized by both cameras at a distance of up to approximately 15 m, independent of depth. The Atlantis camera was better able to detect the living manatees than was the SeaView camera. Because these cameras emit infrared light in order to enhance their water penetration and image detection, there was some concern on the effect of this light on the manatees. However, the infrared light emitted by the cameras appeared to elicit no alarm or aversion from the manatees, and in fact seemed to increase their curiosity about the cameras and to attract them to the cameras. The larger size of the Sea View camera also appeared to draw the attention of the animals to the camera, and to prompt them to approach it in a playful manner. Over the course of this investigation, one NSU Oceanographic Center graduate student has started on a thesis research project. The results of this investigation were presented at the second Florida Marine Mammal Health Symposium, held 7-10 April 2005 in Gainesville, FL (Wright and Keith 2005). The currently available underwater infrared camera technologies evaluated here do not seem to have sufficient detection distances to enable their immediate incorporation into a operator manatee awareness system, in order to utilize the cameras as described above. Our future plans are to approach the manufacturers of these cameras to determine if the technology can be enhanced to enable the cameras to detect manatees at sufficient distance to enable them to be used as described above.