  We present preliminary results of a new quasar survey being undertaken with
multi-colour optical imaging from the Canada-France-Hawaii Telescope. The
current data consists of 3.83 sq. deg. of imaging in the i' and z' filters to a
10 sigma limit of z'<23.35. Near-infrared photometry of 24 candidate 5.7<z<6.4
quasars confirms them all to be low mass stars including two T dwarfs and four
or five L dwarfs. Photometric estimates of the spectral type of the two T
dwarfs are T3 and T6. We use the lack of high-redshift quasars in this survey
volume to constrain the z=6 quasar luminosity function. For reasonable values
of the break absolute magnitude M*_1450 and faint-end slope alpha, we determine
that the bright-end slope beta>-3.2 at 95% confidence. We find that the
comoving space-density of quasars brighter than M_1450=-23.5 declines by a
factor >25 from z=2 to z=6, mirroring the decline observed for high-luminosity
quasars. We consider the contribution of the quasar population to the ionizing
photon density at z=6 and the implications for reionization. We show that the
current constraints on the quasar population give an ionizing photon density
<<30% that of the star-forming galaxy population. We conclude that active
galactic nuclei make a negligible contribution to the reionization of hydrogen
at z~6.
