Estimating Florida manatee (Trichechus manatus latirostris) abundance using passive acoustic methods

Abstract

Manatees are difficult to detect, particularly cryptic populations that inhabit areas with limited water clarity. The effectiveness of using vocal detections to estimate manatee abundance was evaluated in a clear water spring where manatees congregate seasonally. Vocalizations were extracted by a detection classifier that clustered sounds with similar spectral properties. Vocalization counts from recordings in Blue Spring, FL, USA were strong predictors of manatee abundance. The link between independent visual counts and abundance estimates from passive acoustic monitoring was used to provide an estimate of 1.059 (95% confidence interval 0.963–1.127) vocalizations/manatee/5-min, which might be used elsewhere for cue counting of manatees.

Acoustic methods improve the detection of the endangered African manatee

“…Developing improved methods for detecting endangered species where their populations are in decline is crucial to their preservation. Our previous work illustrated the strength of passive acoustics for detecting manatees, and similar methods have been successful in habitats of the West Indian manatee (LaCommare et al, 2008;Gonzalez-Socoloske et al, 2009;Gonzalez-Socoloske and Olivera-Gomez, 2012;Kikuchi et al, 2013;Rivera Chavarria et al, 2015;Guzman and Condit, 2017;Puc-Carrasco et al, 2017;Castelblanco-Martıńez et al, 2018;Rycyk et al, 2021;Rycyk et al, 2022).…”

“…The recorder was retrieved after one-hour deployments (end of survey), and the recordings downloaded for later analysis of the presence of manatee vocalizations (see below for methods). Based on an estimate of manatee vocalization detection range using similar equipment and in a similar environment (Rycyk et al, 2022), manatees might be detected using the PAM method at up to 148 m. A schematic illustration of the implementation of all three methodologies appears in Figure 3.…”

“…However, most vocalizations are between mothers and their calves to maintain contact especially when feeding or traveling in murky waters. Florida manatees have an estimated vocalization rate of 12.7 vocalizations/manatee/60min (Rycyk et al, 2022). It is likely that PAM would be more effective when manatee abundance within the acoustic range increases, as the number of vocalizations would likely increase.…”

“…In addition, manatees produce a variety of vocalizations including squeaks, screeches, whines, and trills (Umeed et al, 2018;Brady et al, 2020;Baotic et al, 2022) shown to be important for their underwater communication and emitted across various behavioral states (Bengtson and Fitzgerald, 1985;O'Shea and Poche, 2006;Brady et al, 2021). Passive acoustics have been used in many studies to monitor manatees and have yielded up to 100% detection frequencies (LaCommare et al, 2008;Kikuchi et al, 2013;Rivera Chavarria et al, 2015;Rycyk et al, 2021;Rycyk et al, 2022). While the above methodologies have been used to monitor other species of manatee (Florida manatees: Rycyk et al, 2022;Antillean manatees: Ramos et al, 2020), they have been rarely implemented with African manatees.…”

“…Passive acoustics have been used in many studies to monitor manatees and have yielded up to 100% detection frequencies (LaCommare et al, 2008;Kikuchi et al, 2013;Rivera Chavarria et al, 2015;Rycyk et al, 2021;Rycyk et al, 2022). While the above methodologies have been used to monitor other species of manatee (Florida manatees: Rycyk et al, 2022;Antillean manatees: Ramos et al, 2020), they have been rarely implemented with African manatees. Rycyk et al (2021) deployed passive acoustic recorders in Lake Ossa in 2020 for two, 3-day periods, resulting in the detection of thousands of vocalizations and enabling the first characterization of African manatee calls; the authors found that African manatee vocalizations are similar to those of other manatee species, with mean fundamental frequency of 4.65 kHz and average duration of 0.181s.…”