by Dr. Beth Brady, Save the Manatee Club; Dr. Eric Angel Ramos, Mote Marine Laboratory; Dr. Nataly Castelblanco-Martinez, Fundación Internacional para la Naturaleza y la Sustentabilidad; and Ayshah Kassamali-Fox, Antioch University
Poorly managed wildlife tourism poses major threats to the survival of endangered species globally. For marine mammals, chronically high levels of boat-based tourism can disrupt behaviors and have other negative impacts contributing to potential population declines.

A relatively unknown population of Antillean manatees—a subspecies of the West Indian manatee—inhabits the Sian Ka’an Biosphere Reserve in Quintana Roo, Mexico, concentrating in underwater sinkholes where they are exposed to daily boat-based tourism throughout the year. Without quantitative assessments of the effects of these activities on manatees and enforcement of local regulations, the preservation of this population is tenuous.
Using funds provided by an AWI Christine Stevens Wildlife Award, we aimed to assess whether manatees are negatively impacted by boat-based tourism through direct disturbance and exposure to high levels of engine noise. We conducted 35 drone flights over several sinkholes to observe manatee behavior and document their interactions with vessels. We also deployed two underwater hydrophones to measure noise levels. Aerial videos were reviewed to compare manatee behaviors before, during, and after tour-boat interactions and in relation to vessel movement characteristics (e.g., speed, orientation, proximity to manatees).
The manatees (20–30 individuals) spent most of the time resting and cavorting at the sinkholes. In one instance, 12 of the 30 boats observed entering the area that day violated regulations by exceeding speed limits and by directly approaching and harassing manatees—sometime encircling them and preventing their escape. Manatees responded to nearby boats by attempting to flee, temporarily leaving the area, diving to the seabed, and clustering together. In contrast, when vessels followed regulations and remained stationary and anchored at a distance from the manatees, we observed few to no disturbance responses.
The overall number of boat detections per day ranged from 20 to 44. The sound levels that manatees were exposed to during tour boat interactions ranged from 96 to 117 decibels. Noise levels were influenced by whether the boats were actively pursuing manatees or passively observing them with engines cut. On days when we were not on site, an estimated 11–33 boats entered the area, with noise levels ranging from 64 to 104 decibels based on hydroacoustic recordings. Although these levels are not enough to damage hearing, they are fairly high, and manatees are exposed to them for up to 10 hours a day. This persistent auditory disruption could potentially decrease the number of animals using the site, disrupt foraging, and affect communication.
Recordings also showed that manatees, including cow/calf pairs, use this site in the evening hours. The presence of calves suggests that this area represents critical habitat for manatees. Overnight vocalizations were detected, but most vocalizations were noted during the day. Interestingly, almost all vocalizations occurred when boats were not present, suggesting that boat presence interferes with communication.
These findings indicate that strengthened regulations and monitoring are urgently needed to mitigate long-term impacts of chronic exposure to unregulated boating activity and the chronic noise levels to this small population of endangered manatees.