Sensory Ecology ~ Sea Turtle Hearing
An understanding of sensory ecology, how animals perceive and respond to their environment, can be a powerful tool for the conservation of endangered species because it can allow us to assess the potential success of actions designed to mitigate particular threats. We have a general understanding of how sea turtles perceive and respond to certain visual, magnetic, and chemical cues, but we understand very little about how they perceive and respond to acoustic cues. To determine what types of sounds sea turtles perceive in their environment, I measured the underwater and aerial hearing sensitivities of several species and age-classes of sea turtle (juvenile green, Chelonia mydas, hatchling leatherback, Dermochelys coriacea, and hatchling hawksbill, Eretmochelys imbricata, sea turtles by recording auditory evoked potential responses (AEPs) to tonal stimuli. AEPs are electrical responses produced by the central auditory nervous system in response to stimulation by sound that is detected by the ear. My research has shown that sea turtles are most sensitive to low-frequency acoustic stimuli ~<2,000 Hz both in air and underwater, and are likely able to detect many of the low-frequency anthropogenic sources of sound in the marine environment.
Fisheries Bycatch ~ Sensory-based Bycatch Reduction Strategies
Bycatch, or the incidental capture of non-target species in fishing gear, is one of the major challenges facing marine resource managers. Bycatch poses a significant threat to many populations of sea turtles, because these animals have low reproductive rates and delayed maturation and, as a consequence, are particularly sensitive to high rates of removals. The goal of this research is to develop and test innovative BRTs that reduce bycatch (sea turtles, marine mammals, elasmobranchs, etc.) and maintain target fish catch rates and market value. An understanding of sensory ecology can guide the development of successful bycatch reduction technologies (BRTs) such as acoustic deterrent devices (ADDs) and light-emitting diodes (LEDs). ADDs are low-intensity sound sources that have been used to reduce the by-catch of some marine mammals, but their efficacy has not been evaluated for sea turtles. Past assessments have dismissed the potential of ADDs to reduce sea turtle by-catch because of the similar hearing sensitivities of sea turtles and fishes and the subsequent expectation that, even if the devices were effective in reducing the by-catch of turtles, ADDs would reduce the catch of target species. However, in fisheries for flatfish, which have very poor low frequency hearing, ADDs could be detectable by turtles, but not the target species. We have shown that these BRTs can be successful in reducing sea turtle bycatch while maintaining target catch and are examining their efficacy in gillnet and pound net fisheries in Mexico and the United States.
Behavioral Ecology ~ Responses to Acoustic Stimuli
While an understanding of hearing offers insights into what signals organisms can detect, it is important to understand how individuals and groups will behaviorally respond to these signals. Using biologging tools we are examining behavioral responses of sea turtles to acoustic cues designed to deter them from potentially dangerous construction areas. We use acoustic telemetry tags (AMX, Loggerhead Instruments, Inc) to simultaneously measure the underwater acoustic sound field and the three-dimensional movements of turtles to examine how turtles behaviorally respond to sounds. These novel methodologies for sea turtles allow us to examine behavioral responses of turtles to anthropogenic and natural sounds and examine the soundscape in which they live.
Habitat Use ~ Marine Protected Species
Data on species distribution and range are necessary to effectively evaluate the status and trends of populations over time. However, these data are often difficult to obtain, particularly for marine species with small population sizes and large geographic ranges. To help fill these data gaps I have worked to develop interactive publicly available databases of habitat use by marine protected species.
As part of my Master’s research I examined multi-year aerial survey data to generate digital atlas of seal haul-out sites in the Gulf of Maine. I went on to analyze these data using spatial and quantitative statistics to describe seal distribution over time. The results are collated in an interactive online database on OBIS-SEAMAP.
While working with the Wider Caribbean Sea Turtle Network I developed a digital interactive atlas of sea turtle nesting habitat in the Wider Caribbean Region to support research and conservation efforts within the region. In collaboration with over 100 sea turtle managers, researchers and conservationists I collated data describing nesting beach characteristics, sea turtle activity, monitoring status, and threats. The nesting atlas is available as an interactive database online at OBIS-SEAMAP.
On a smaller spatial scale, I have also programmed and deployed satellite tags on nesting female loggerhead sea turtles (Caretta caretta) in North Carolina. I analyzed location, dive, and temperature data as part of a larger research project designed to estimate marine mammal, sea turtle, and sea bird distribution, abundance, and habitat use in the Mid-Atlantic. Tracks for each of the three turtles tagged (Pati, Pointe and Grace) can be found on the seaturtle.org satellite tracking site as part of the North Carolina Long-term sea turtle monitoring project.