The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals, Mirounga angustirostris

Abstract

Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate ͑ATOC͒ sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level ͑SPL͒. The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 Pa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels ͑SPL͒ measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 Pa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.

Development of an animal-borne “sonar tag” for quantifying prey availability: test deployments on northern elephant seals

“…Given the off-axis source levels and much shorter durations (150 μs) of the sonar tag's signals, the sound levels received by the seal were certainly much lower than this threshold for temporary loss of hearing sensitivity. We were mindful of the importance of examining the potential impact of the sonar tag on the test animals since, for instance, translocated northern elephant seals instrumented with passive acoustic data loggers that were exposed to the Acoustic Thermometry of the Ocean Climate (ATOC) lowfrequency sound source exhibited subtle changes in their diving behavior [34]. Unusual dive patterns were in some instances observed associated with the first dive in a 4-h pinging interval.…”

“…Each sonar tag was duty cycled on a 4 h on and 4 h off basis. This allowed comparisons of the animals' dive behavior during periods when the tag was pinging to periods when it was not, based on a similar set of dive characteristics as used in an earlier study of translocated elephant seals exposed to the Acoustic Thermometry of the Ocean Climate (ATOC) low-frequency sound source [34]. At the time of animal release, the tag was programmed to be off.…”

“…Juvenile elephant seals translocated short distances away from the Año Nuevo State Reserve north of Santa Cruz, California, are known to return to the Año Nuevo or a nearby colony after time periods of hours to days, making a series of dives to depths of up to 900 m during their return transit [32]. The behavior of translocated animals thus closely mimics their natural behavior, allowing new tag technologies to be tested under real-world conditions and within short amounts of time [e.g., [33][34][35]. The focus of the present work is on data recorded by the prototype sonar tag and associated depth-and position-logging tags during a series of test deployments.…”

Studying the behaviour and sensory ecology of marine mammals using acoustic recording tags: a review

“…The most reliable of these relate to changes in dive profile, orientation, swimming effort and vocal output (Costa et al 2003, Nowacek et al 2004, Miller et al 2009). In species for which there are consistent foraging cues, the proportion of time devoted to foraging or the number of prey capture attempts may be relevant metrics (Miller et al 2009).…”

Acoustic Response and Detection of Marine Mammals Using an Advanced Digital Acoustic Recording Tag(Rev 3)

“…Early examples of acoustic recording tags are those of Burgess et al (1998), developed for deepdiving elephant seals, and Costa et al (2003), who used such a tag to study the effects of an Acoustic Thermometry of Ocean Climate (ATOC) transmitter on the dive patterns of seals. Peter Tyack has been developing tags to identify the vocalizations of cetaceans since 1982 at WHOI , Tyack and Recchia 1991, Burgess et al 1998.…”