Page 29 - April 2008

to assess hearing sensitivity of untrained non-captive animals by measuring auditory evoked potentials (Casper et al., 2003; Nachtigall et al., 2005; Finneran and Houser, 2006; Houser et al., 2007).
Acoustic data logger tags are relatively inexpensive, easi- ly programmed, miniature sensor packages that are attached by suction cups to the body surface and can be carried by even small marine mammals and sea turtles. The tags record sounds as received by the animal simultaneously with records of swimming and diving movements as well as social sounds or sonar use by the animals themselves. They can even be configured to record heart rate and respiration if needed. These tags have been used to study the underwater behavior and calls of blue whales off the California coast and beaked whales in the Bahamas, Canary Islands, and Mediterranean Sea (Johnson et al., 2004; Madsen et al., 2005). Madsen et al. (2006) used acoustic data logger tags to quantify the sound received by foraging sperm whales from seismic air gun emissions in a CEE in the Gulf of Mexico. They found that simple spherical spreading models could not be used to pre- dict sound levels received by the animals, and that the received sound contained significant energy all the way up to 3 kHz when whales were near the surface.
Less than 10 years ago, knowledge of hearing in fish and marine mammals was generated through behavioral studies using captive animals trained to participate in hearing test procedures. This behavioral approach was expensive, time- consuming, and limited to only a very small number of cap- tive individuals and species. An alternative to obtaining behavioral measures of hearing sensitivity is an electrophysi- ological technique based on the measurement of small volt- ages produced by the brain in response to sound. These volt-
Fig. 3. Satellite tag on a sperm whale.
movement and behavior. An example of the latter is the Autonomous Acoustic Recording Packages (ARPs) devel- oped at the Scripps Institution of Oceanography (Wiggins, 2003). These packages are mounted on the sea floor and pro- vide continuous monitoring of whale migrations and region- al populations for a year or more. ARPs have been deployed to record baleen whale sounds in the Bering Sea, Beaufort Sea, Gulf of Alaska, off the coast of southern California, near the West Antarctic Peninsula, and near Hawaii. NOAA Fisheries uses these types of passive acoustic recording instruments in their marine mammal censuses.
Since 2003, three biennial International Workshops on the Detection and Classification of Marine Mammals Using Passive Acoustics (Halifax 2003, Monaco 2005, and Boston 2007) have produced three special issues of peer-reviewed scientific jour- nals that represent the state-of-the-art in signal processing for automatic detection, classification and localization of multiple marine species. These signal processing techniques have been applied to small deployable hydrophone
arrays as well as to development of the Marine Mammal Monitoring on Navy Ranges (M3R) program. This program was funded by ONR to develop data acquisition and signal processing systems to detect, classify and localize different groups of whales on a range in real time by recording sounds through the range’s existing array of bottom-mounted hydrophones. Classification is limited to families of whales (e.g., beaked whales, sperm whales, pilot whales, etc.) that echolocate while foraging. With support of CNO N45, this system is now being ported to multiple ranges to be used for monitoring marine mammal activ- ity; however, these systems can also be used to study the natural behavior of animals and their responses to sound exposure.
Perhaps the two most important recent technological developments for studying the effects of sound on marine animals in the wild are acoustic data log- ger tags that can be used to examine their behavior in response to received sound (Burgess et al., 1998; Johnson and Tyack, 2003), and field portable instrumentation
Fig. 4. Clockwise from top left: Auditory evoked potential (AEP) measurements using surface electrodes on a stranded rough toothed dolphin (Cook, Manire and Mann, U. South Florida); needle electrodes and head- phones for sound stimulus on elephant seal pup in air (Houser and Reichmuth, UCSC); needle electrodes on reef fish (Hastings, ARL Penn State); and surface electrodes on white whale in air with sound stimulus pre- sented with jaw phone (Finneran and Houser, SSC San Diego).
Ocean Noise and Marine Animals 27