During the Start of the Gulf War, I remember reading that the US Navy Dolphins were having problems adjusting to the Persian Gulf. The reason is the Persian Gulf is less salty then the rest of the ocean, given it narrow shape, tight exit to the ocean and massive flow of fresh water from the Euphrates and Tigris Rivers in Iraq and the various rivers flowing into it from Iran.
The Dolphins had a hard time adjusting to the lack of Salt. Dolphins are sea creatures built around "normal" salt levels. In areas where salt is less due to river input, they can swim for a while, then have to move out. Salt water animals keep pumping salt OUT of they body, due to the massive influx from the sea they are swimming in. Fresh water fish and other animals have a body system the keeps salt INSIDE their body, since they is little if any salt in the water they swim in. Some fish do operate in both types of water, but only for short periods of time (Salmon up the rivers to spawn and then down rivers to the sea is the most commonly known type of both fresh and salt water fish). The Fresh water Dolphins of the Yangtze (now believed extinct) and the Amazon are believed to be descendant from ocean going dolphins, but have lost they ability to operate in salt water, for they operate in fresh water.
Please note, the article I read did NOT say the Dolphins were NOT doing what they were trained to do, but that they were getting sick due to the reduce level of salt in the waters of the Gulf and what the Dolphins needed were frequent removal to areas further out in the ocean to recover.
I suspect the problems with Dolphins adjusting to the level of Salt in the Water is the reason for the shift, the other sea of concern right now is the Black Sea, and it is even worse, it is a salt water top over a fresh water bottom. Now the Black sea has dolphins, but I can NOT find a site that say they interbreed out side of the Black Sea, i.e. while the same type of dolphins as elsewhere, how much have they adopted to the special conditions of the Black Sea, On the other hand all are small enough to travel the Bosporus and the Straits of the Dardanelles to mix with other dolphins, so may NOT be a problem for the Dolphins of the Black Sea for the same reason it is not a problem for native Dolphins of the Persian Gulf (i.e. the Dolphins when they start to get sick due to the lack of salt, just go out to the deep ocean and leave they bodies adjust).
My point is the time off task needed for the Dolphins may be the real reason for the change, the Robot does NOT have to be pulled back to deep ocean after a couple of weeks in the Persian Gulf.
http://blacksea-education.ru/dolphins.shtml
Persian Gulf Dolphins may have been affected by Sonar in 2008:
http://www.guardian.co.uk/world/2007/nov/02/iran.environment
http://www.atimes.com/atimes/Middle_East/JA08Ak02.html
http://en.wikipedia.org/wiki/Military_dolphin
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