  We present submillimetre observations of the J = 3-2 rotational transition of
12CO, 13CO and C18O across over 600 sq arcmin of the Perseus molecular cloud,
undertaken with HARP, a new array spectrograph on the James Clerk Maxwell
Telescope. The data encompass four regions of the cloud, containing the largest
clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A
new procedure to remove striping artefacts from the raw HARP data is
introduced. We compare the maps to those of the dust continuum emission mapped
with SCUBA (Hatchell et al. 2005) and the positions of starless and
protostellar cores (Hatchell et al. 2007a). No straightforward correlation is
found between the masses of each region derived from the HARP CO and SCUBA
data, underlining the care that must be exercised when comparing masses of the
same object derived from different tracers. From the 13CO/C18O line ratio the
relative abundance of the two species ([13CO]/[C18O] ~ 7) and their opacities
(typically tau is 0.02-0.22 and 0.15-1.52 for the C18O and 13CO gas
respectively) are calculated. C18O is optically thin nearly everywhere,
increasing in opacity towards star-forming cores but not beyond tau(C18O)~0.9.
Assuming the 12CO gas is optically thick we compute its excitation temperature
(around 8-30 K), which has little correlation with estimates of the dust
temperature.
