Date of Award
Doctor of Philosophy (PhD)
anthropogenic noise, behavioral ecology, biologging, Florida manatee
Underwater noise from human activities can impact the behavior and physiology of aquatic animals, with potential cumulative effects on populations. To accurately estimate the population-level effects of noise disturbance, it is crucial to quantify individual exposure and investigate responses to noise disturbance. This study aims to quantify Florida manatee exposure and the individual variability of responses to anthropogenic noise. Gathering information on how much time individuals dedicate to specific behaviors is crucial to understanding species' ecology and investigating anthropogenic factors' impacts on populations. Therefore, in Chapter 1, I developed a machine-learning model that classifies movement sensor data collected from biologging devices on Florida Manatees. The model classified 7464 hours of sensor data with a global accuracy of 76%. The time spent on various behaviors varied by individual, and overall, manatees spent 58%, 41%, and 1% of their time resting, traveling, and engaging in other behaviors, respectively. Our findings demonstrate the potential of combining biologging and machine learning to obtain large-scale baseline behavioral data, which can increase the applicability of behavioral data in understanding life-history tradeoffs and the impact of human activities on wildlife. Although the effects of underwater noise received a lot of attention, above the water surface, such as from aircraft, is rarely considered in noise budgets. As such, in Chapter 2, We used multi-week sound and movement recording tags and GPS trackers to quantify exposure and responses of Florida manatees to airplane noise. Airplane exposures were most frequent when manatees attended warm water refuges and a feeding habitat close to airports. Although we did not detect flight or diving responses, the location of international airports near critical habitats suggests that manatees must often endure airplane noise to access essential resources, and the potential cumulative impacts of these exposures should be considered. While watercraft is an important source of mortality and disturbance for Florida manatees, individual exposure rates are seldom available. To fill this knowledge gap, in Chapter 3, we characterized individual manatee exposure to watercraft noise using long-term animal-borne acoustic tags and GPS trackers. The total number of exposures ranged from 16 to 377, and deployments had from 1 to 32 days with at least one exposure detected. We found that exposures were significantly correlated to proximity to marinas, distance to seagrass beds, bathymetry, and protected areas for most deployments. Differences in exposure rates must be accounted for when strategizing management to mitigate the lethal and sublethal effects of watercraft presence and noise on the Florida population. Even though manatee responses to watercraft approaches have been previously described, fewer studies explored intra-individual variability in such responses. Therefore, in Chapter 4, we conducted a preliminary analysis to describe the different responses to watercraft noise one individual can display. Using the acoustic record of the DTAGs, we detected instances of watercraft noise. We classified responses into 12 categories based on fluke stroke and depth changes in response to noise exposure. Although noise levels were important to predict the response probability, our preliminary approach allowed for describing different response classes with potentially distinct energetic requirements and acoustic and environmental drivers. We recommend that future studies include direct measures of energy expenditure. Moreover, the role of exposure duration, watercraft speed and proximity, depth, and behavioral state in modulating response types should be explored.
Ribeiro Guimaraes Dombroski, Julia, "MANATEES AND NOISE: INDIVIDUAL EXPOSURE AND BEHAVIORAL RESPONSES TO DISTURBANCE" (2023). Dissertations - ALL. 1683.
Available for download on Thursday, June 12, 2025