Innovative Measures for Mitigating Potential Impacts on Sea Turtles During Seismic Surveys
Authors: van der Wal S. , Eckert S. A. , Lopez-Plana J. O. , Hernandez W. , Eckert K. L. 
Published: March 2016

Sound in the ocean emanates from a variety of natural and anthropogenic sources. Low frequency sounds, such as those produced by shipping, drilling, and seismic sonar travel long distances in the ocean environment and affect marine animals both physiologically and behaviorally. The effects of anthropogenic marine sound can be short- or long-term, and can affect a single individual (e.g., disrupted feeding routines, hearing damage) or entire populations (e.g., reproductive success). While some animals can and do avoid sound, repeated exposures to sound sources can cause marine animals to habituate to or become unable to hear the sound, potentially increasing the risk of long-term physiological effects. Concern is usually directed toward marine mammals, which use sound for communication and navigation and often rely on sound perception and interpretation for survival, but less is known about the effects of anthropogenic noise on sea turtles.

Sea turtles hear well underwater, and their greatest hearing sensitivity lies within the envelope of sound produced by seismic sources. Therefore, temporal and spatial patterns of habitat use are highly relevant to consideration of mitigation schemes. To increase our understanding of habitat use, garner data useful in developing mitigation protocols and to evaluate the potential effects on sea turtles during 3D seismic survey by the Three Oil and Gas Companies Joint Venture (hereinafter, the Joint Venture) in the territorial waters of the Dutch Caribbean island of Aruba, VHF radio transmitters and GPS-equipped satellite platform transmitter terminals (PTT) were attached to four species of gravid turtles when they came ashore to nest on the island's beaches. Pathways of ingress and egress from Aruban waters and the extent to which these coincided with the seismic survey zone were documented.

The Joint Venture developed response protocols requiring all seismic operations to cease if a turtle approached the vessel to within 500 m – and to remain so until, based on VHF monitoring, the turtle cleared the area. In addition, seismic surveys were avoided within 100 m of the 50 m depth contour around the island, and around all subsurface features that rise to a depth of 50 m from the surface. The objective was to avoid exposing turtles to harmful sound levels from the acoustic source on the survey vessel, and to avoid displacing turtles from critical habitats, including nesting beaches.

This report presents the findings of the two initiatives implemented by the Joint Venture, Wider Caribbean Sea Turtle Conservation Network (WIDECAST, a regional scientific organization), and Turtugaruba (an Aruba-based sea turtle conservation organization) with the field data obtained during the survey in the offshore of Aruba. This project implemented best practices for seismic surveys in areas where sea turtles are present, including establishment of sensitive areas based on data-supported assessments of turtle presence, home ranges and high use areas, as well as use of vessel-based VHF or acoustic monitoring for transmitter- or transponder-equipped turtles.