Measuring the behavior and response to sound of beaked whales using recording tags. Johnson, M. & Tyack, P. .
  author      = {Mark Johnson and Peter Tyack},
  title       = {Measuring the behavior and response to sound of beaked whales using recording tags},
  comment     = {Results from the study are directed at two strategies to reduce beaked
	whale mortality: first, with a specification of how and when these
	animals vocalize, it may be possible to develop systems for passive
	acoustic detection of beaked whales. Since beaked whales are so difficult
	to sight, acoustic detection is a critical method to monitor for
	the presence of these sensitive species before and during sonar trials.
	The second, longer-term strategy is to determine what factors heighten
	the risk of stranding and to identify opportunities to minimize these.
	If risk assessments continue to highlight an urgent need to define
	safe exposure limits for beaked whales, we propose to plan a pilot
	study on the behavioral responses of beaked whales to low levels
	of sonar-like sounds.
	This is the description of a project, with many interesting facts!
	Although the NOPP project only began in May 2004, we have already
	made a number of significant advances. With leverage from SERDP and
	U.S. Navy (N45) funding, we performed lengthy field seasons in our
	study sites in Italy and the Canary Islands. We have now placed tags
	on 7 Cuvier's and 3 Blainville's beaked whales. Our data set contains
	97 hours of on-animal recording including 44 deep dives and a remarkable
	9 hour set in which two Cuvier's beaked whales were tagged contemporaneously
	in the same group. Three whales (2 Cuvier's and 1 Blainville's) were
	tagged with high sampling-rate (192kHz) stereo DTAGs, developed this
	year, providing full-bandwidth recordings of the two species. The
	double tagging of Cuvier's beaked whales also provided an opportunity
	to estimate the source level and beamwidth of the click sounds. With
	this, and the movement information recorded by the tags, we can begin
	estimating the practicality of passive acoustic detection of these
	species as a mitigation measure.
	Several key results have already been obtained in the first year of
	the project. Using data from the new high-sampling rate tag, we have
	characterized the vocalizations of Cuvier's and Blainville's beaked
	whales over their full frequency band. These vocalizations consist
	of two distinct types of clicks which we refer to as regular and
	buzz clicks. Both click sounds occur at the base of deep foraging
	dives as shown in Fig. 1. Regular clicks occur at relatively stable
	intervals of 0.2 to 0.4s throughout the base of the dive while buzz
	clicks occur in occasional short bursts with inter-click-intervals
	of about 5ms. Echoes from approaching targets in the water, recorded
	by the tags, confirm an echolocation function of both click types
	and represent the first time that echoes from prey have been recorded
	on a marine mammal. Based on our findings with sperm whales [Miller
	2004], we associate buzz clicks with the terminal phase of a capture
	sequence. Recordings of buzzes with echoes from prey, made by the
	tag, provide an unprecedented opportunity to investigate prey selection
	and capture, and to estimate foraging efficiency [Madsen 2005]. Regular
	clicks from both beaked whale species have a long duration (200µs)
	and a distinctive frequency-modulated sweep characteristic, making
	them unique amongst the odontocetes studied to date. This kind of
	click may be tailored to discriminate targets in a highly cluttered
	acoustic environment such as we have observed in the tag recordings.
	In contrast, the buzz click is of short duration (about 60µs) and
	is broadband without obvious modulation. The ability to produce two
	distinct click types has not been described for other odontocetes
	and may represent a specialization for deep-water foraging. These
	results have relevance in understanding the habitat selection of
	beaked whales and in designing passive acoustic monitoring systems
	for these species. In particular, the distinctive regular clicks
	may hold the key to discriminating beaked whale sounds from those
	of ubiquitous species such as dolphin that appear to be less sensitive
	to sonars. We have submitted a paper describing the broadband clicks
	of Cuvier's beaked whale [Zimmer, subm.] and are currently preparing
	a paper on those of Blainville's beaked whale.
	COOL POINT I HAD NOT SEEN BEFORE: Beaked whales are most often observed
	in small groups at the surface and are seen to dive synchronously.
	The use of a stereo acoustic recording tag this year has provided
	an opportunity to study the behavior of the group during foraging
	dives. Regular and buzz clicks from untagged whales in the group
	are frequently heard in the stereo tag recording and the sounds from
	individuals can be distinguished by their angle-of-arrival. We have
	been able to count the number of individuals present during a foraging
	dive and compare it to surface observations of the same group. In
	each case, most orall of the whales in the group are present in the
	deep dive, including juveniles. This suggests that dive duration
	may be determined by the least-capable (e.g., smallest) animal in
	the group, an interesting counterpoint to the traditional optimal
	foraging paradigm. If, as is likely, vocalizations mediate this cohesion,
	then there is a risk that anthropogenic sound such as from sonars
	may disrupt group communication and thus behavior.},
  file        = {Johnson&Tyack.pdf:Johnson&Tyack.pdf:PDF},
  owner       = {Tiago},
  subdatabase = {postdoc, beaked},
  timestamp   = {2007.08.13},
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