# Bioacoustic Classification of Antillean Manatee
## 2 Materials and Methods
### Data Source  
As described in [5] manatee vocalizations consist of single-note calls with several harmonics with frequency modulation, overtones and other nonlinear elements. For Antillean manatees recorded in Panama wetlands, the average fundamental frequency is around 3 kHz with a range between 0.7 and 8.1 kHz, and average duration is 362 ms with high variability (\(\pm\) 114 ms). Harmonic components typically reach around 20 kHz. Examples of vocalizations are shown in Figure 2.  
Three databases were used in this study, prepared from audio clips recorded on the permanent monitoring sites in Changuinola and San San rivers, using Wildlife Acoustics SM3M bioacoustics programmable recorders (Maynard, MA, USA), placed 1 m above river floor at 2-3 depth. A detailed map of the river localizations and the surroundings is shown in Figure 3. The sampling frequency of the recorders was set at 96 kHz.  
The first database included 507 curated manatee vocalizations and 177 sounds of the habitat (including noises produced by other species that co-exist in the habitat such as frogs and snapping  
Figure 1: Analysis methodology for the classification of vocalizations.  
shrimps, and low frequencies noises produced by currents and waves hitting the hydrophone unit). These sounds were obtained from audio clips recorded on two of the permanent monitoring sites (Figure 3), one in the Changuinola River (S1) and one in San San River (S3). The vocalizations and noise sounds were extracted from 65 (2-min) audio clips recorded from 1 May to 7 May 2018 from the Changuinola River and 62 (2-min) audio clips recorded from 7 July to 21 July 2017 from the San San River.  
The vocalizations (positive samples) and noise sounds (negative samples) correspond to the true positive and false positive outputs, respectively, of the detection stage presented in [5]. This detection stage was based on the analysis of the autocorrelation of the signals in the wavelet domain using a mean-based threshold in each level. From the Changuinola River 313, and 128, true positives and false positive signals were detected in the audio clips, respectively. In the River San San, 194 true  
Figure 3: Location of manatee recording monitoring sites in the Changuinola and San San rivers, in Bocas del Toro, Panama.  
Figure 2: Three examples of different manatee vocalizations recorded in the San San and Changuinola rivers.  
positives and 49 false positive signals were detected. It is noteworthy that vocalizations in this database presented a low SNR affected by background noise or other interferences. Some vocalizations only presented one harmonic component or were degraded. Thus, this database represents signals with the regular field acquisition conditions.  
The second database, consisting of an additional new set of 166 noises (negative samples), were obtained from the same audio files using a more sensitive threshold (i.e., median-based threshold) in the detection stage. This set was prepared to be able to achieve class balance in some of the proposed experiments (see Section 2.4).  
The third database included a set of 200 vocalizations from 20 different manatees (10 vocalizations per manatee). This database was prepared by visually inspecting spectrograms in the recordings of 20 days with the greater number of vocalizations determined by using the detection stage proposed in [5], in the whole data set of audio clips, from April 2015 to May 2018, and from the four permanent monitoring sites. This preparation process entailed the search of vocalizations with the same features in each day to have a group of vocalizations generated, likely, by the same individual. This database generally presented vocalizations with a higher SNR or quality that the first database.  
Each element of the databases consists of short audio clips with a duration between 70 ms to 800 ms.