image: A Seaglider, equipped with a hydrophone and acoustic recorder, awaits deployment off of Southern California July 2016. The glider is capable of diving to 1,000 m, and communicates via satellite. It is being used to survey for marine mammals. view more
Credit: Danielle Harris
Washington, D. C. November 30, 2016 -- Hearing is a vital sense for marine mammals who use it to forage, communicate and navigate. Many of these mammals produce specific vocalizations that can be used to identify the species and track their locations via acoustic monitoring. Traditionally, scientists have used underwater microphones to listen for marine mammals, either on the seafloor or towed behind a boat. But now scientists can use autonomous underwater vehicles, gliders and floats specially equipped with hydrophones, to listen to marine mammals in ways impossible until now.
The direct comparison of these methods conducted by a team of researchers spanning both U.S. coasts will help us to better collect data to monitor marine life for both conservation and management of protected species.
The use of gliders and floats in passive acoustic monitoring helps address the spatial and temporal tradeoff of stationary and towed instruments.
"Towed instruments provide great spatial coverage. A boat can 'mow the lawn' over a large area in a relatively short period of time, while stationary recorders on the seafloor have great temporal coverage, but they record only within a certain range of the hydrophone," said Selene Fregosi, a researcher at the Cooperative Institute for Marine Resources Studies, Oregon State University and National Oceanic and Atmospheric Administration in Newport, Oregon. "A mobile, autonomous recorder can both cover a large area and survey for weeks or months at a time, without the high cost of operating a large research vessel." Understanding how the methods compare and what their strengths and limitations are is a key to the monitoring of sea life.
During the 172nd Meeting of the Acoustical Society of America and the 5th Joint Meeting with Acoustical Society of Japan, being held Nov. 28-Dec. 2, 2016, in Honolulu, Hawaii, Fregosi will explain how the research team tested the two methods simultaneously by deploying their glider and float in the area where cabled, bottom mounted hydrophones were installed. The cabled hydrophone array localized where animals were, and by using those locations researchers evaluated the performance of the glider and float. By recording simultaneously on all the different instruments, data on the capabilities of the autonomous systems was collected.
The most challenging factor in this testing was fighting bad weather to deploy and recover the instruments.
"We had a very short window of time we could work in the area of the cabled array when there wasn't a Navy exercise, so we didn't really have much time to wait for good weather days. Plus, we had communication problems with the glider halfway through the deployment," Fregosi said. "We weren't getting regular messages every 6 hours as usual, so going out to recover it was a bit like looking for a needle in a haystack. But we got lucky that the glider managed to communicate right when we needed it to."
The test of how well these instruments can detect different species of marine mammals, and over what distances, is just the first step towards using acoustic data collected by gliders and floats to estimate marine mammal density and abundance. These are critical measurements for conservation and management of these protected species.
The next step is to take these comparisons and use the baseline detection capabilities of these instruments to better interpret results in a biological context. Fregosi looks forward to putting these tools to work. "I am hopeful that the use of gliders and other autonomous instruments will become more widespread. They can lead to data collection in areas that weren't feasible to study before," Fregosi said.
###
Presentation 3pABb3, "Simultaneous recordings of marine mammal calls by a glider, float, and cabled hydrophone array," by Selen Fregosi is at 3:15 p.m. HAST, Nov. 30, 2016 in Room Coral 2.
MORE MEETING INFORMATION
The 172nd Meeting of the Acoustical Society of America
The meeting is being held Nov. 28-Dec. 2, 2016 in Honolulu, Hawaii
USEFUL LINKS
Main meeting website: http://acousticalsociety.org/content/5th-joint-meeting-acoustical-society-america-and-acoustical-society-japan
Technical program: http://acousticalsociety.org/asa2016fall.abstractcentral.com/planner.jsp
Meeting/Hotel site: http://acousticalsociety.org/content/5th-joint-meeting-acoustical-society-america-and-acoustical-society-japan#hotel
Press Room: http://acoustics.org/world-wide-press-room/
WORLD WIDE PRESS ROOM
In the coming weeks, ASA's World Wide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay-language papers, which are 300-1200 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio, and video. You can visit the site during the meeting at http://acoustics.org/world-wide-press-room/.
PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact Emilie Lorditch (elorditc@aip.org, 301-209-3029) who can also help with setting up interviews and obtaining images, sound clips, or background information.
LIVE MEDIA WEBCAST
A press briefing featuring the acoustics of snapping shrimp and coconut beetles plus, how speech sounds influence female vocal attractiveness will be webcast live from the conference on Wednesday, Nov. 30th from 10 - 11 a.m. HAST in room Iolani I.
ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world's leading journal on acoustics), Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. For more information about ASA, visit our website at http://www.acousticalsociety.org.