  Arrays of acoustic receivers are an integral part of present and potential
future Cherenkov neutrino telescopes in the deep sea. They measure the
positions of individual detector elements which vary with time as an effect of
undersea currents. At the same time, the acoustic receivers can be employed for
marine science purposes, in particular for monitoring the ambient noise
environment and the signals emitted by the fauna of the sea. And last but not
least, they can be used for studies towards acoustic detection of
ultra-high-energy neutrinos. Measuring acoustic pressure pulses in huge
underwater acoustic arrays with an instrumented volume of the order of 100 km^3
is a promising approach for the detection of cosmic neutrinos with energies
exceeding 1 EeV. Pressure signals are produced by the particle cascades that
evolve when neutrinos interact with nuclei in water, and can be detected over
large distances in the kilometre range. In this article, the status of acoustic
detection will be reviewed and plans for the future - most notably in the
context of KM3NeT - will be discussed. The connection between neutrino
detection, position calibration and marine science will be illustrated.
