Environmentally friendly parametric alarm for alerting marine mammals of approaching vessels

Marine mammals are vulnerable to boat, barge, and ship collisions. Although more commonly identified and reported in busy coastal areas, collisions are not restricted to shipping lanes or shallow water environments. A common denominator is that they all occur near the surface. Here the acoustical laws of reflection and propagation significantly limit the ability of marine mammals to hear and locate the sounds of approaching vessels. Acoustic measurements from controlled ship passages through vertical hydrophone arrays demonstrate the confluence of factors that poses auditory detection challenges for both whales and manatees. A highly directional, environmentally-friendly, low intensity underwater parametric alarm has been developed to mitigate these challenges & safely alert marine mammals of approaching vessels. The efficacy has been demonstrated with wild manatees. Ninety-five percent of manatees during alarm-on trials elicited avoidance reactions while only 5% of manatees during alarm-off trials elicited any change in behavior. The mean distance at which manatees reacted to boat approaches during alarm-on trials was also 20 m compared to only 6 m for alarm-off trials (F= 218.4 df = 1, p< 0.01). Counter-intuitive to speed reduction laws, slow vessels can be more difficult for marine mammals to detect and locate. The low intensity, directional alarm assures animals can detect & locate vessels at distances sufficient to avoid injury. [Funded by DOD Legacy Natural Resource Management Program, USFWS Permit MA063561-4.]