TiHo researchers investigate the hearing of the marine mammals.
Researchers from the Institute for Terrestrial and Aquatic Wildlife Research of the University of Veterinary Medicine Hannover Foundation (TiHo) are investigating the hearing of gray seals (Halichoerus grypus) under the leadership of Professor Dr. Ursula Siebert and Dr. Andreas Ruser.
They published the first results in the online specialist magazine Plos one (www.plosone.org). The investigations were financed by the German Federal Agency for Nature Conservation (BfN) in order to increase knowledge about the effects of underwater noise on marine mammals. They are part of a multi-year, extensive BfN research program. The measuring system was supported by Technical Center Army Office 71 of the German Armed Forces.
“We urgently need to learn more about how well and in which frequency range gray seals hear,” says Professor Dr. Ursula Siebert, Head of the institute. “The last scientific publication on this topic dates back to 1975.”
Noise pollution in the sea is continuously increasing: shipping traffic, construction works in the sea, blasting, sound cannons to search for crude oil or the use of sonar devices stress the animals. The scientists need precise data about the hearing of gray seals in order to assess the effects of underwater noise on the animals. This seal species, along with porpoises and seals, is among the most common marine mammals in the North and Baltic Seas.
For their current study, the researchers investigated six gray seals from rearing stations. Dr. Andreas Ruser explains: “Basically, we proceeded according to the principle which we know from ear specialists.”
In contrast to humans, however, animals cannot say when they hear a tone, so the challenge for the researchers was to find out whether the seals perceive a tone or not. The researchers sedated the gray seals shortly before they were to be released into the wild. Then they played tones to them and measured the nerve impulses transmitted from the cochlea to the auditory nerve. As soon as the animals woke up again, the researchers were able to release them into the wild.
Since seals close their external ear channel when sedated, it is impossible to treat them with ultrasound using speakers. “We therefore used specially adapted in-ear headphones,” explains Ruser. The researchers found out that gray seals, similar to humans, can hear in a frequency range between 1,000 and 20,000 hertz and are much more sensitive than previously known in a range higher than 3,000 hertz.
Furthermore, there are indications not yet confirmed that gray seals can also hear above 20,000 hertz. “Using this method, however, we can only prepare a so-called air audio diagram for wild animals, which means that measurements can only be carried out in the air. Sound waves are transmitted in a different manner under water. We therefore assume that gray seals hear even higher frequencies under water.”
Next, Ruser and his colleagues want to examine this difference with gray seals trained and held in human hands at the University of Southern Denmark, Odense: The gray seals must therefore “learn” to signalize whether they hear something, first above and then under water. The seals are thus to be trained to show a defined reaction as soon as they hear a tone. This training is carried out in the pool of the respective seal facility.
The tones are then played for the gray seals under controlled conditions using headphones or loudspeaker in the air and loudspeaker or hydrophones under water. “We are looking forward to the further results, particularly with regard to the hearing of the seals under water,” says Professor Siebert. “We are hoping for reliable evidence that shows to what extent seals are affected by the increasing noise pollution in the North and Baltic Seas.”
Gray seals are the biggest wild predators in Germany. They can live up to 35 years. With a length of 230 centimeters and an average weight of 220 kilograms, males are considerably larger than females, which can be up to 180 centimeters in length and may weigh 150 kilograms.
The employees of the Institute for Terrestrial and Aquatic Wildlife Research work in Hannover and at a branch of the TiHo in Büsum in Schleswig-Holstein. The focal points of aquatic wildlife research are basic research, applied research and monitoring. The aim is to investigate the biology and ecology of marine mammals and to assess the influence of humans on animals, their health and their population.
In-air evoked potential audiometry of grey seals (Halichoerus grypus) from the North and Baltic Seas
Andreas Ruser, Michael Dähne, Janne Sundermeyer, Klaus Lucke, Dorian S. Houser, James J. Finneran, Jörg Driver, Iwona Pawliczka, Tanja Rosenberger, Ursula Siebert
Plos one, DOI: 10.1371/journal.pone.0090824
For technical questions, please contact
Dr. Andreas Ruser
University of Veterinary Medicine Hannover Foundation
Institute for Terrestrial and Aquatic Wildlife Research
Phone: +49 511 953-8156
Sonja von Brethorst | idw - Informationsdienst Wissenschaft
Molecular trigger for Cerebral Cavernous Malformation identified
26.11.2015 | EMBO - excellence in life sciences
Peering into cell structures where neurodiseases emerge
26.11.2015 | University of Delaware
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.
Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...
The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...
Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.
In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...
In laser material processing, the simulation of processes has made great strides over the past few years. Today, the software can predict relatively well what will happen on the workpiece. Unfortunately, it is also highly complex and requires a lot of computing time. Thanks to clever simplification, experts from Fraunhofer ILT are now able to offer the first-ever simulation software that calculates processes in real time and also runs on tablet computers and smartphones. The fast software enables users to do without expensive experiments and to find optimum process parameters even more effectively.
Before now, the reliable simulation of laser processes was a job for experts. Armed with sophisticated software packages and after many hours on computer...
Researchers at Heidelberg University have devised a new way to study the phenomenon of magnetism. Using ultracold atoms at near absolute zero, they prepared a...
25.11.2015 | Event News
17.11.2015 | Event News
21.10.2015 | Event News
26.11.2015 | Ecology, The Environment and Conservation
26.11.2015 | Materials Sciences
26.11.2015 | Earth Sciences