Loggerhead turtles dive in response to airgun sound exposure

Abstract

Visual observations of the behavior of over 150 loggerhead turtles (Caretta caretta) were collected over a period of 2 weeks during a seismic survey in the Mediterranean Sea off Algeria in September and October 2009. All turtles were observed during active operation of an airgun array that had a peak source level of 252 dB re 1 muPa. Recordings from three hull-mounted hydrophones allowed concurrent estimation of near-surface airgun array source signatures and sound exposure levels. Of the 53% of turtles that were successfully visually tracked until they had passed more than 100 m behind the seismic vessel, 51% dived at or before their closest point of approach to the airgun array. Among animals that dived, approximately 20% did so immediately following an airgun shot, often showing a startle response that was clearly distinguishable from the predominant basking behavior. Turtle dive probability as a function of distance from the airgun array and sound exposure level will be considered in detail. The observed diving behavior may be interpreted as an avoidance response and may have negative consequences for turtles if it interferes with thermoregulation (basking) or results in inhabitual energy expenditures.