Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Manatee hearing good enough to sense approaching motorboats

12.04.2012
Grazing sea grass along the subtropical Florida coast, manatees would seem to have a peaceful life. But motorboats and other watercraft can injure the mammals, sometimes shattering their ribcages or leaving scars from collisions.

Joe Gaspard from the Mote Marine Laboratory and Aquarium, USA, explains that many factors put manatees at risk and it isn't clear why the animals are so vulnerable to human activity. For more than 14 years, Mote research has focused on how manatees use their senses to perceive their environment in an effort to understand the factors that put manatees at risk.

Their studies have already shown that manatees' vision is poor, compounded by the turbid and tannic waters where they spend much of their lives. But can manatees hear boats? And can they hear them above the cacophony of sounds in their natural environment? Sound is absorbed less in water than in air, potentially allowing it to travel farther. It also travels five times faster in water than in air, theoretically warning the animals earlier of an approaching threat, Gaspard said. Teaming up with Gordon Bauer, Roger Reep and David Mann, and a group of trainers from the aquarium, Gaspard tested the hearing of two resident manatees, Buffett and Hugh – the world's only manatees trained to participate in behavioural research and husbandry procedures – to find out what they are capable of hearing. The discovery, published in The Journal of Experimental Biology at http://jeb.biologists.org, indicates that manatees can hear within the frequency range where boats operate but lead to new questions about why manatees remain at risk.

'Buffett and Hugh are very cooperative and picked up on the elements of the study quickly', remembers Gaspard, who worked with Kim Dziuk, Adrienne Cardwell and LaToshia Read to train the animals to swim down to a listening station 1 m beneath the surface. Switching on a light to indicate to the animals that a test was about to start, the team then trained the manatees to touch a yellow response paddle in return for a tasty fruit or vegetable snack when they heard a sound. They also trained the manatees to stay in place (in return for another snack) when they heard nothing. Once Hugh and Buffett had got the task in hand, the team tested their hearing by selecting a particular sound frequency (pitch) and gradually lowering the volume of the sound until the manatee could no longer hear it. Plotting these 'hearing thresholds' on a graph, the team could see that the manatees had good hearing between 8 and 32kHz and could even hear sounds as low as 0.25kHz – so long as they were quite loud. However, they were even more amazed when Buffett appeared to be able to hear ultrasonic frequencies as high as 90.5kHz. 'Buffett did the task but refused to continue after the first round at that frequency, so we think it was aversive or annoying', Gaspard recalls.

Intrigued by the manatees' apparently sensitive hearing, the team then tested how well the mammals performed when the sounds were accompanied by background noise. Playing test tones – ranging from 4 to 32kHz – against background noise centered on the same pitch, the team recorded the difference between the volume of the tone and background noise when the manatee could no longer distinguish the tone. Plotting the critical ratio – the level at which the background noise swamped the manatee's hearing – against pitch for each animal, the team saw that the manatees struggled to hear lower and higher pitched sounds above background noise. However, their hearing was much sharper at 8kHz – the frequency at which manatees communicate – where they could still distinguish tones that were only 18.3dB louder than the background.

So, it appears that manatees should be able to hear approaching motorboats above background noise — but it's much more difficult to know whether manatees can always focus on these sounds in nature, Gaspard says. 'Manatees might be less aware of these sounds when they are sleeping, eating or performing other activities related to their daily lives that require their full attention,' says Gaspard. "There are also a multitude of environmental factors that come into play. Understanding how animals use their various senses is a complex process. Could their sense of touch also be playing a role here? We are working on that question now."

IF REPORTING ON THIS STORY, PLEASE MENTION THE JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org/content/215/9/1442.abstract

REFERENCE: Gaspard, J. C. III, Bauer, G. B., Reep, R. L., Dziuk, K., Cardwell, A., Read, L. and Mann, D. A. (2012). Audiogram and auditory critical ratios of two Florida manatees (Trichechus manatus latirostris). J. Exp. Biol. 215, 1442-1447.

This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT permissions@biologists.com

Kathryn Knight | EurekAlert!
Further information:
http://www.biologists.com
http://jeb.biologists.org/content/215/9/1442.abstract

More articles from Life Sciences:

nachricht Warming ponds could accelerate climate change
21.02.2017 | University of Exeter

nachricht An alternative to opioids? Compound from marine snail is potent pain reliever
21.02.2017 | University of Utah

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Start codons in DNA may be more numerous than previously thought

21.02.2017 | Life Sciences

An alternative to opioids? Compound from marine snail is potent pain reliever

21.02.2017 | Life Sciences

Warming ponds could accelerate climate change

21.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>