  In continuation of previous work, numerical results are presented, concerning
relativistically counter-streaming plasmas. Here, the relativistic mixed mode
instability evolves through, and beyond, the linear saturation -- well into the
nonlinear regime. Besides confirming earlier findings, that wave power
initially peaks on the mixed mode branch, it is observed that, during late time
evolution wave power is transferred to other wave numbers. It is argued that
the isotropization of power in wavenumber space may be a consequence of weak
turbulence. Further, some modifications to the ideal weak turbulence limit is
observed. Development of almost isotropic predominantly electrostatic --
partially electromagnetic -- turbulent spectra holds relevance when considering
the spectral emission signatures of the plasma, namely bremsstrahlung,
respectively magneto-bremsstrahlung (synchrotron radiation and jitter
radiation) from relativistic shocks in astrophysical jets and shocks from
gamma-ray bursts and active galactic nuclei.
