Abstract
In 2014, a working group funded by the National Oceanic and Atmospheric Administration (NOAA), National Science Foundation (NSF), Office of Naval Research (ONR), and Acoustical Society of America (ASA) convened to establish sound exposure guidelines for fishes and sea turtles (Popper et al., 2014). The group provided a review of literature on the biological significance of sound, hearing sensitivity, anthropogenic noise sources, and noise impacts. In doing so, they identified a number of data gaps that were limiting factors in the establishment of exposure guidelines for sea turtles. They concluded with a set of interim guidelines until further research fills these data gaps. Among their recommended research priorities, they identified the need to determine the hearing sensitivity of all sea turtle species across all life stages.
Sea turtles inhabit temperate, tropical, coastal, and offshore marine environments. These habitats are subject to anthropogenic noise from shipping, military, and energy development activities (Hildebrand 2009). Noise at various levels has the potential to affect marine organisms by causing direct physical injury, inducing temporary or permanent threshold shifts in hearing sensitivity, inducing metabolic stress, disrupting behavior, displacing individuals from preferred locations, and masking biologically important sounds needed for prey detection, predator evasion, and navigation (Rako-Gospić and Picciulin, 2019).
In coastal and offshore habitats, seismic surveys pose a risk of repeated high amplitude exposures to marine life over large spatial and temporal scales (Estabrook et al., 2016; Wiggens et al., 2016), the effects of which remain poorly understood (Elliot et al., 2019). Impact and vibratory pile driving are also sources of high amplitude noise, albeit localized to smaller areas in shelf waters. Shipping, while not as loud, is continuous and omnipresent in many shelf waters (Hildebrand, 2009; Estabrook et al., 2016; Wiggens et al., 2016; Rice et al., 2014). Additional, intermittent sources of high amplitude noise that occur in both shelf and oceanic habitats include military sonar and explosives (Hildebrand, 2009; Accomando et al., 2024).
The biological significance, or role of sound for sea turtles, and the extent to which they may be affected by anthropogenic noise, is currently not well understood. A number of studies have demonstrated behavioral responses of sea turtles to anthropogenic noise sources (O’hara and Wilcox, 1990; McCauley et al., 2000; DeRuitter and Doukara, 2012; Kastelien et al., 2023). Over the past decade, knowledge of the hearing capabilities of sea turtles has greatly advanced. Previous studies of hearing in loggerhead (Caretta caretta) (Bartol et al., 1999; Lavender et al., 2014; Martin et al., 2012), green (Chelonia mydas) (Piniak et al., 2016; Ridgway et al., 1969), and leatherback (Dermochelys coriacea) (Dow Piniak et al., 2012) sea turtles revealed hearing capabilities up to 1,600Hz, with greatest sensitivities falling between 100 and 500Hz. However, very little hearing data exist for several species and age classes. These data gaps limit our ability to accurately assess potential impacts to all life stages and species of sea turtles from anthropogenic sound and to develop successful mitigation measures.
Our current knowledge suggests that sea turtles can detect much of the low-frequency, high-intensity anthropogenic sound in the ocean, including pile driving, low-frequency active sonar, and oil and gas exploration and extraction. The apparent low-frequency specialization of sea turtle hearing is reason for concern that they may be impacted by anthropogenic noise. Anthropogenic noise primarily occurs at low frequencies due to the physical nature of sound sources and the propagation efficiency of low-frequency sound in water (Richardson, 1995; Hildebrand 2009).