  We study the quantum entanglement of the quasiparticle pairs emitted by
analogue black holes. We use a phenomenological description of the spectra in
dispersive media to study the domains in parameter space where the final state
is non-separable. In stationary flows, three modes are involved in each sector
of fixed frequency, and not two as in homogeneous situations. The third
spectator mode acts as an environment for the pairs, and the strength of the
coupling significantly reduces the quantum coherence. The non-separability of
the pairs emitted by white holes are also considered, and compared with that of
black holes.
