There are two mammal species that have developed a hunting and investigation system that relies on sound projection: these are the toothed whales and the bat family. Recent research suggests that dolphins and echolocating bat species may have developed similar brain structures due to this phenomenon.
Among the many allegations made by animal-rights lobbyists is the issue of the dolphins use of echolocation in captive environments. There seems to be two opposing arguments promoted regarding the use of echolocation in captive dolphins.
1. Animals do not use their sonar in captive environments and are effectively mute.
2. A contradictory argument is that if they do use their echolocation it causes them discomfort and distress as sound signals bounce off the walls of their exhibits. This is sometimes referred to as "the wall of mirrors" effect.
The first of these arguments is easily refuted as a huge amount of research has been undertaken on the use of dolphins sonar and communication for many decades.
Indeed, pioneering research that made known that dolphins use a form of echolocation was revealed in research with animals in captivity in the early 1950s by researchers such as Arthur McBride at the Marine Studios (Marineland of Florida) in the 1940s and later Dr Winthrop Kellogg in the 1950s (see over view in Norris, 1991).
Moreover, in some public demonstrations animals are trained to display their sonar abilities by being blindfolded and can be seen successfully seeking and retrieving objects for their trainers.
In fact, during the research for the UK's Review of Dolphinaria the authors, Dr. Margaret Klinowska and Dr. Susan Brown, visited a number of dolphinaria and successfully recorded animals making both vocalisations and echolocation (Klinowska and Brown, 1986).
Later Dr Klinowska and the late Dr David Goodson engaged on experimental research using captive and wild bottlenose dolphins to develop acoustic tags to be placed on monofilament fishing nets which dolphins find very difficult to image using their echolocation systems. This can lead to the serious issue of entrapment and drowning of dolphins in various fishing industries globally.
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| Acoustic research with captive dolphins a Flamingoland in UK |
The second allegation cited is that dolphins can use their echolocation within the captive environment but suffer distressing acoustic artefacts due to sounds bouncing uncontrollably of the walls of their exhibits. This allegation is partially correct that the sounds the animals produce (when using their echolocation) bounce back from the walls of their tanks in their exhibits but that is exactly how echolocation works. However the allegation is not correct in that it does not take into account how dolphin echolocation works and the role the dolphin itself plays in the production and interpretation of the sounds it sends and receives.
Research has shown that a dolphins echolocation is very sophisticated and it is this very sophistication that makes it an exquisite tools the dolphins exploit when hunting or exploring their environment; the sophistication of the dolphins echolocation is believed by some to be the reason these animals have large brains.
In using their echolocation, the dolphins are fully capable of controlling their echolocation beam in both direction and strength; it is not a blunt instrument which cannot be controlled by the animal. As stated above it is primarily used for hunting or investigating objects.
One aspect of the dolphins senses aside from its hearing is that work done with the bottlenose dolphin demonstrates that these animals have very good eyesight both in the water and the air (Ridgway, 1991). Dolphins in fact will rely on their eyesight in clearwater conditions and will switch off their sonar only to re-engage it when hunting or re-examining objects they have seen that they may be curious or suspicious of.
Therefore, it can be seen that allegations that dolphins have problems with the use of their echolocation capabilities in captive environments is false. This is not to say that dolphins could have acoustic problems in both their wild and captive environment but this is unrelated to echolocation or indeed communication sounds. These issues in captivity may relate to the engineering and build of their exhibit and its infrastructure such as the operation of life-support systems and these are issues that can be addressed and resolved. Unfortunately, the situation for some of these animals in the wild is far more problematic and less easy to solve. Ironically, the answer to the questions of acoustic pollution and how wild cetaceans deal with such things are in some part being answered by research with animals in captive environments.
Dr. Paul Nachtigall on the echolocation and hearing sensitivity control in cetaceans.
References:
Klinowska, M. and Brown, S. (1986).A Review Of Dolphinaria, London: Department of the Environment.
Norris, K. (1991). Looking at Captive Dolphins. In Pryor, K. and Norris, K. (Eds) Dolphin Societies: Discoveries and Puzzles. Oxford: University of California Press.
