A variety of "see-in-the-dark" technologies have been evaluated with the objective of adapting them to detect Florida manatee (Trichechus manatus latirostris) aggregations in specific highuse areas, such as warm water refuges in the winter time. Once it is possible to passively detect manatee aggregations in these sites, the construction of boater awareness signs that would indicate how many manatees are in the area, on a real-time basis, is envisioned. The contention is that boaters would be more likely to obey speed restrictions if these restrictions were accompanied by this type of information. The ability to do this also might enable such speed restrictions to be more flexible, and only enforced when manatees are actually present. This would make such speed restrictions more palatable to boaters.
The three technologies that I have examined are: (1) infrared cameras that detect infrared (heat) radiation emitted by all warm objects, (2) "night-vision" viewers that emit infrared radiation and then use the reflected radiation to generate an image, and (3) “night-shot" video cameras that also emit infrared radiation and then record the images generated by the reflected radiation. Each of these technologies have advantages and disadvantages.
The true infrared cameras provide the best images, at least in air. Water absorbs most infrared radiation, and so these cameras cannot penetrate water to image submerged objects such as manatees. I knew this prior to beginning my investigations, but thought that this technology might be able to detect manatee exhalations, which I anticipated would be warmer than the ambient air. It turns out that this is not the case, in that manatees appear to exhale air from their nostrils at close to ambient temperature. It has long been known that desert animals, and other marine mammals such as northern elephant seals (Mirounga angustirostris) also do this, and that this constitutes a water conservation mechanism. However, these cameras can detect the actual nostril openings of the manatees. Their images can also be sharply focused, and are not diminished by ambient light sources such as streetlights. This technology can also be used during daylight hours. The major drawback of these cameras is their expense, $15-30,000.00, and the need for a portable video recorder (also expensive) to capture images.
Because of the limited success of the infrared cameras, I also evaluated a night-vision scope. These are much less expensive, $300-500.00, which makes their deployment more economically feasible. They also appear to be able to penetrate the water to a depth of 0.5-1.0 meter. However, the images generated by this technology are of poorer quality, and this quality is deleteriously impacted by other ambient light sources. In addition, these scopes cannot be used during daylight hours. Capturing images on film also requires a 35 mm camera and adaptor.
I also found that many current models of "handy-cam" videocassette recorders have a "nightshot" capability, that utilizes a similar technology to the night-vision scopes, and can be purchased for $300-500.00. I anticipated that the ability to directly record the images detected by the camera would be a distinct advantage, as would the ability to switch from regular daytime video recording to nighttime video recording with the flip of a switch. However, the drawback of these video cameras is that they do not penetrate the water as well as the night-vision scopes, resulting in poor quality video images.
All of these technologies have their advantages and disadvantages which limit their application to the proposed boater awareness system. I believe that the night-vision technology might be best adapted to the system that I envision, but this would require more time and funding to fully explore and develop. I are also investigating the possibility that the manufacturer of the expensive infrared cameras might donate one of their demonstration models to Nova Southeastern University, which would enable us to more completely explore the use of this technology, and its potential for modification for my system. The "night-shot" video cameras might likewise be able to be modified to enhance their water penetrating ability and image quality. It might also be possible to adapt this technology to other applications, such as placing one on the bow of the boat, and projecting the image at the helm of the boat, so that the boat operator could, possibly, detect manatees in the water, or after dark, that they would not otherwise see. The appeal of this type of technology is that it is already familiar to most people, and thus learning to use it would not be a major burden on the operator. The cost of such a system would also probably not result in a major increase in the cost of the boat itself.
Over the course of this investigation, one NSU Oceanographic Center graduate student has almost completed her thesis, and another has started on her thesis. Preliminary results of this investigation were presented at the second annual Southeast and Mid-Atlantic Marine Mammal Symposium (SEAMAMMS) held 12-14 April 2002 in Conway, SC. Ms. Paine is currently in the final stages of completing her master’s degree thesis.
Paine, A.L, W.E. Baxley, and E. O. Keith. (2002). Investigating the feasibility of thermal infrared imaging technology for passive marine mammal detection. Southeast and Mid-Atlantic Marine Mammal Symposium. 12- 14 April, Conway, SC.
Paine, A. (In Prep). Investigating Applications of Thermal Infrared Technology for Passive Marine Mammal Detection. M.S. Thesis. Oceanographic Center, Nova Southeastern University, Ft. Lauderdale, FL
Finally, I believe that there has been a significant scientific spin-off from my investigation. The inability to detect manatee exhalations using the true infrared camera, or any of the technologies I examined, provides the first evidence that I are aware of that manatees exhale air at near ambient temperature, which as was mentioned above, has been documented in other animals as a water conservation mechanism. In their natural environment manatees almost never encounter fresh water, and thus must derive all of their water either from the food they eat (preformed water) or from metabolism. This necessitates a variety of water conservation mechanisms, such as the excretion of a highly concentrated urine, a thick water impervious skin, and a lack of thermoregulatory sweating. I have here provided evidence of yet another important adaptation that enables manatees to exist without ever needing to drink fresh or salt water.
Manatee Avoidance Technology: Contract #FWC 01-02-14
Final Report to the Florida Fish & Wildlife Conservation Commission
Edward O. Keith. 2002. Boater Manatee Awareness System .Final Report to the Florida Fish & Wildlife Conservation Commission . http://nsuworks.nova.edu/occ_facreports/91.