jremington:
There has recently been a real breakthrough in underwater acoustic communications.Researchers as Newcastle University in the U.L, have developed spread spectrum nanomodems: very cheap ($70 instead of $7000), very low power, small and yet long range (km).
A better way to transmit messages underwater
I would hope that commercial versions of these might appear in the next couple of years.
The data rate is only 40bps but that meets the OPs requirement of a maximum of 2000bps.
Transmitting power consumption drops from 35W to 1W which has to be a good thing, though it is still high.
I worry a bit though about whether or not they are testing what effect these devices might have on sea creatures. The range is given as 2km and they are broadcasting on several frequencies. If the devices are small, low cost, and low power they could start being used in far greater numbers than current technology.