Acoustic methods improve the detection of the endangered African manatee

The African manatee (Trichechus senegalensis) is an elusive, data-deficient, and endangered species which inhabits marine and freshwater systems throughout Western and Central Africa. A major challenge in understanding the species ecology and distribution is the difficulty in detecting it using traditional visual surveys. The recent invasion of Giant Salvinia (Salvinia molesta) at the most important site for the species in Cameroon further limits their detectability and may restrict their movements and habitat use. To investigate methods’ effectiveness in detecting African manatees, we conducted monthly vessel surveys from which visual point scans, 360° sonar scans, and passive acoustic monitoring were conducted simultaneously at ten locations and over 12 months in Lake Ossa, Cameroon. Manatee detection frequency was calculated for each method and the influence of some environmental conditions on the methods’ effectiveness and manatee detection likelihood was assessed by fitting a binary logistic regression to our data. Detection frequencies were significantly different between methods (p < 0.01) with passive acoustics being the most successful (24.17%; n = 120), followed by the 360° sonar scan (11.67%; n = 120), and the visual point scan (3.33%; n = 120). The likelihood of detecting manatees in Lake Ossa was significantly influenced by water depth (p = 0.02) and transparency (p < 0.01). It was more likely to detect manatees in shallower water depths and higher water transparency. Passive acoustic detections were more effective in uninvaded areas of the Lake. We recommend using passive acoustics to enhance African manatee detections in future surveys

Application of acceleration data loggers to classify the behavior of captive Amazonian manatees (Trichechus inunguis)

The Trichechus inunguis is endemic to the Amazon region. Observation is nearly impossible because of the turbid water, which consequently hinders study of their behaviour. In this study, we deployed the acceleration data loggers to 9 captive Amazonian manatees to classify their behaviour at INPA, Brazil. The experiments were also recorded by video camera. We classified four types of behaviours: inactive on the bottom, walking on the bottom, surfacing and swimming. Inactive and walking on the bottom were classified using standard deviation (SD) of dive depth and longitudinal acceleration. The SD of dive depth shows the low variability in inactive and walking on the bottom (ranged from 0.0 to 0.1 m), the SD of longitudinal acceleration shows the low variability in inactive (from 0.00 to 0.01 ms(-2)), high variability in walking on the bottom (from 0.01 to 0.15 ms(-2)). Mean classification accuracy was 87.1% and 84.9% during inactive and walking on the bottom, respectively. 6 manatees were fed floating vegetables during experiment, and they showed a characteristic of long surfacing during feeding time. This characteristic was probably a fair reflection of their natural behavior, as wild Amazonian manatees prefer floating and emergent aquatic plants

Application of acceleration data loggers to classify the behavior of captive Amazonian manatees (Trichechus inunguis)

The Trichechus inunguis is endemic to the Amazon region. Observation is nearly impossible because of the turbid water, which consequently hinders study of their behaviour. In this study, we deployed the acceleration data loggers to 9 captive Amazonian manatees to classify their behaviour at INPA, Brazil. The experiments were also recorded by video camera. We classified four types of behaviours: inactive on the bottom, walking on the bottom, surfacing and swimming. Inactive and walking on the bottom were classified using standard deviation (SD) of dive depth and longitudinal acceleration. The SD of dive depth shows the low variability in inactive and walking on the bottom (ranged from 0.0 to 0.1 m), the SD of longitudinal acceleration shows the low variability in inactive (from 0.00 to 0.01 ms(-2)), high variability in walking on the bottom (from 0.01 to 0.15 ms(-2)). Mean classification accuracy was 87.1% and 84.9% during inactive and walking on the bottom, respectively. 6 manatees were fed floating vegetables during experiment, and they showed a characteristic of long surfacing during feeding time. This characteristic was probably a fair reflection of their natural behavior, as wild Amazonian manatees prefer floating and emergent aquatic plants

The implications of turning behaviour performed by Amazonian manatees after release into the wild

Sirenians have dichromatic colour vision and tactile hairs but have not developed underwater echolocation. Amazonian manatees (Trichechus inunguis) live in turbid water and it has been unclear how they understand their surroundings. In this study, we recorded the 3D movements of two captive-raised Amazonian manatees. The results revealed that the manatees always swam in a circular pattern. Both animals used slower, narrower turning motions as they approached the flooded forests, which is abundant in aquatic vegetation. Therefore, we suggest that these two manatees swam in a circular pattern to detect all directions of their surroundings especially using sensitive facial bristles. © 2011 Japan Ethological Society and Springer

Detection of manatee feeding events by animal-borne underwater sound recorders

Studies of the feeding behaviour of aquatic species in their natural environment are difficult, since direct observations are rarely possible. In this study, a newly developed animal-borne underwater sound recorder (AUSOMS-mini) was applied to captive Amazonian (Trichechus inunguis) and Antillean (Trichechus manatus manatus) manatees in order to directly record their feeding sounds. Different species of aquatic plants were offered to the manatees separately. Feeding sounds were automatically extracted using a custom program developed with MATLAB. Compared to ground truth data, the program correctly detected 65–79% of the feeding events, with a 7.3% or lower false alarm rate, which suggests that this methodology is a useful recorder of manatee feeding events. All manatees foraged during both the daytime and night-time. However, manatees tended to be less active and masticated slower during the night than during the day. The manatee mastication cycle duration depended on plant species and individual. This animal-borne acoustic monitoring system could greatly increase our knowledge of manatee feeding ecology by providing the exact time, duration and number of feeding events, and potentially the plant species being fed on

The implications of turning behaviour performed by Amazonian manatees after release into the wild

Sirenians have dichromatic colour vision and tactile hairs but have not developed underwater echolocation. Amazonian manatees (Trichechus inunguis) live in turbid water and it has been unclear how they understand their surroundings. In this study, we recorded the 3D movements of two captive-raised Amazonian manatees. The results revealed that the manatees always swam in a circular pattern. Both animals used slower, narrower turning motions as they approached the flooded forests, which is abundant in aquatic vegetation. Therefore, we suggest that these two manatees swam in a circular pattern to detect all directions of their surroundings especially using sensitive facial bristles. © 2011 Japan Ethological Society and Springer