  We present an exact expression for the quasinormal modes of acoustic
disturbances in a rotating 2+1 dimensional sonic black hole (draining bathtub
fluid flow) in the low frequency limit and evaluate the adiabatic invariant
proposed by Kunstatter. We also compute,via Bohr-Sommerfeld quantization rule
the equivalent area spectrum for this acoustic black hole, and we compute the
superradiance phenomena for pure spinning 2+1 black holes.
