We present new optical spectroscopy for 342 R < 18 galaxies in the Shapley Supercluster ( and 198 supplementary galaxies ) , obtained from 8 hour integrations with the AAOmega facility at the Anglo-Australian Telescope . We describe the observations and measurements of central velocity dispersion \sigma , emission line equivalent widths and absorption line indices . The distinguishing characteristic of the survey is its coverage of a very wide baseline in velocity dispersion ( 90 per cent range \sigma = 40 - 230 { km s ^ { -1 } } ) , while achieving high signal-to-noise ratio throughout ( median 60 per Å at 5000 Å ) . The data quality will enable estimates of Balmer-line ages to better than 20 per cent precision even for the faintest galaxies in the sample . Significant emission at H \alpha was detected in \sim 30 per cent of the supercluster galaxies , including \sim 20 per cent of red-sequence members . Using line-ratio diagnostics , we find that the emission is LINER-like at high luminosity , but driven by star-formation in low-luminosity galaxies . To characterise the absorption lines , we use the classical Lick indices in the spectral range 4000–5200 Å . We introduce a new method for applying resolution corrections to the line-strength indices . We define a subset of galaxies with very low emission contamination , based on the H \alpha line , and fit the index- \sigma relations for this subset . The relations show the continuation of the familiar trends for giant galaxies into the low luminosity regime , with little change in slope for most indices . Comparing the index - \sigma slopes against predictions from single-burst stellar population models , we infer the scaling relations of age , total metallicity , [ Z/H ] , and \alpha -element abundance ratio , [ \alpha /Fe ] . To reproduce the observed index - \sigma slopes , all three parameters must increase significantly with increasing velocity dispersion . Specifically , we recover : Age \propto \sigma ^ { 0.52 \pm 0.06 \pm 0.10 } , Z/H \propto \sigma ^ { 0.34 \pm 0.04 \pm 0.07 } , and \alpha /Fe \propto \sigma ^ { 0.23 \pm 0.04 \pm 0.06 } ( where the second error reflects systematic effects ) , derived over a decade baseline in velocity dispersion , \sigma = 30 - 300 { km s ^ { -1 } } . The equivalent slopes for the subset of galaxies with \sigma > 100 { km s ^ { -1 } } are similar for age and Z/H . For \alpha /Fe , a steeper slope is recovered for the high- \sigma subset , \alpha /Fe \propto \sigma ^ { 0.36 \pm 0.07 } . The recovered age - \sigma relation is shown to be consistent with the observed evolution in the giant-to-dwarf galaxy ratio in clusters at redshifts z = 0.4 - 0.8 . In a companion paper , we determine the age , [ Z/H ] and [ \alpha /Fe ] for individual galaxies , and investigate in detail the distribution of galaxy properties at fixed velocity dispersion .