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. 2023 Nov 17;18(11):e0294600.
doi: 10.1371/journal.pone.0294600. eCollection 2023.

Manatees display diel trends in acoustic activity at two microhabitats in Belize

Beth Brady  1 , Carly Sarbacker  2 , Jake Andrew Lasala  1 , Maria Maust-Mohl  3 , Kristi Ashley Collom  4 , Linda Searle  5 , Laura J May-Collado  2   6 , Eric Angel Ramos  2   7
Affiliations

Manatees display diel trends in acoustic activity at two microhabitats in Belize

Beth Brady et al. PLoS One. .

Abstract

Many marine mammals exhibit diel trends in vocal production, which can provide information on habitat use and behavioral activity. In Belize, Antillean manatees (Trichechus manatus manatus) commonly inhabit small depressions in the substrate or deep-water coves known as "resting holes". Determining if manatees exhibit diel temporal trends in their call production rate and call types between microhabitats can provide insights into their diurnal and nocturnal activity patterns. Here, we investigate the diel vocalization patterns of wild Antillean manatees in two adjacent resting holes off of St. George's Caye, Belize. Recordings of manatees were made using a bottom-mounted hydrophone located near a reef barrier reef for nine days in July of 2017 and ten days in January of 2018. To explore if and how manatee acoustic activity differs between sites, we compared the number of calls per hour, the number of manatee positive hours, the number of tonal and atonal sounds, and the number of boats detected across sites. A total of 370 hours of acoustic recordings were analyzed resulting in the detection of 3,262 calls. There were no significant differences in the number of manatee calls produced per hour between sites. The average number of calls produced by manatees decreased over the course of several days. The proportion of tonal calls decreased with hours after sunset and increased in boat presence. These results suggest manatees in this region may exhibit different diel activity patterns which appear to be influenced by the characteristics of the environment. These findings can support ongoing conservation and management efforts to safeguard species in Belize.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1
Map of the study area at St. George’s Caye in Belize and images of Site A (top right) and Site B (top left). The SoundTrap HF300 was deployed in a seagrass channel near the resting hole for Site A (white circle), a man-made dredged channel, and on seagrass flats near a resting hole for Site B (white circle). The basemap in the top map was generated with drone-based orthomosaic images of St. George’s Caye, gathered and constructed by Eric A. Ramos.
Fig 2
Fig 2. Spectrograms of wild Antillean manatee vocalizations recorded near two resting holes during this study.
The top spectrograms show tonal vocalizations and the bottom two spectrograms show atonal vocalizations. Spectrogram parameters: Hanning window; 90% overlap; 512 FFT.
Fig 3
Fig 3. Bar graph depicting the number of Antillean manatee vocalizations detected during each recording hour at the recording sites (Total of 370 hr recordings from three deployments of the SoundTrap HF300).
Fig 4
Fig 4. Average number of boats detected per hour at each recording site.
Fig 5
Fig 5. Manatee positive hours (MPH) in relation to the day of sampling.
Sampling differed due to timing and the number of days; however, MPH provides an unbiased view of manatee presence across sites. MPH significantly declined over the sampling period regardless of site.
Fig 6
Fig 6. Boxplot depicting the number of manatee calls detected in relation to the hour of the day.
Although not significantly different (GLM, blue line with 75% Confidence Interval), the number of calls decreased over the course of the day.
Fig 7
Fig 7. The proportion of tonal calls over all calls in relation to the number of hours after sunset and the number of boats present.
See this image and copyright information in PMC

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