Characterization of Resting Holes and Their Use by the Antillean Manatee (<I>Trichechus manatus manatus</I>) in the Drowned Cayes, Belize

Abstract

In the Drowned Cayes area of Belize, manatees (Trichechus manatus manatus) are commonly observed resting in depressions in the substrate, locally referred to as manatee resting holes. To understand why manatees prefer locations with resting holes, the physical and environmental attributes of the depressions were characterized and diurnal and nocturnal use by manatees at four resting hole sites were documented over two summers. Twelve resting hole sites were compared with 20 non-resting hole sites in the Drowned Cayes, using water depth, substrate type, vegetation, water velocity, salinity, and water temperature. Four resting holes were chosen for repeated diurnal and nocturnal observations, during which sea and weather conditions were recorded in addition to the presence/absence of manatees. Resting holes were significantly deeper and had slower surface water velocity than areas without resting holes. A total of 168 point scans were conducted over 55 d, resulting in 39 manatee sightings over two summers. There was a significant difference in the number of sightings between research years and between day and night scans. Given the large number of resting holes in the Drowned Cayes, many of which are in sheltered areas with slow currents, it is possible that manatees select these spots based on the tranquility of the water and environment. The combination of slow currents, protection from waves, low numbers of boats, and nearby seagrass beds would make these ideal resting areas. These findings have implications for the conservation of important manatee habitat.

Movement patterns of Antillean manatees in Chetumal Bay (Mexico) and coastal Belize: A challenge for regional conservation

“…. The substrate in and around the resting holes tended to be a silty mixture of mud and sand, which was easily compressed and resuspended(Bacchus et al 2009). In northern Chetumal Bay sand, soft silt and clay sediments are present (de Jesú s-…”

Bottlenose Dolphins and Antillean Manatees Respond to Small Multi-Rotor Unmanned Aerial Systems

“…Flight tracks were examined in Google Earth Pro to groundtruth measurements of manatees' positioning and travel distances (m). Habitats at sighting locations were categorized as follows: seagrass bed (dense or patchy), lagoon, channel, channel edge, cove, reef, or resting holes (holes in the substrate where manatees frequently rest; Bacchus et al, 2009).…”

Using Pooled Local Expert Opinions (PLEO) to Discern Patterns in Sightings of Live and Dead Manatees (Trichechus senegalensis, Link 1785) in Lower Sanaga Basin, Cameroon

“…In any case, several seasonally fluctuating factors have been shown to affect the occurrence, activity, and movements of (West African) manatees. These factors include: water temperature: warm-water refugia are necessary for manatee survival as the species is intolerant of temperatures below 20°C [ 62 , 64 – 65 ]; water current: manatee energetic expenditures increase with higher currents [ 6 , 13 , 65 ], which is most likely in rainy season, though critical limits are unknown; water salinity: Florida manatees that inhabit marine environments require regular access to fresh water sources [ 59 – 60 ]and there is also evidence that those living in freshwater systems require some access to sodium [ 59 ]; hence, manatee movements are closely tied to seasonal changes in fresh and salt water flows, whether along river streams or between lagoons and the sea [ 9 , 72 ]; water levels: the high depths in wet season facilitate escape from intruders, access to bank vegetation, and movements to flooded forests and swamps [ 6 , 9 ] but encounters are more likely at sites with 2–5 m depth [ 9 , 13 , 71 , 73 ]; bottom substrate: manatees prefer muddy substrates which, unlike rocky ones, provide resting holes and allow benthic activities e.g., gliding and rooting [ 12 , 14 , 73 ]. …”