  We present several measurement schemes for accessing separability criteria
for continuous-variable bipartite quantum systems. Starting from moments of the
bosonic mode operators, criteria suitable to witness entanglement are expressed
in terms of multimode spin observables via the Jordan Schwinger map. These
observables are typically defined over a few replicas of the state of interest
and can be transformed into simple photon-number measurements by passive
optical circuits. Our measurement schemes require only a handful of
measurements, thereby allowing one to efficiently detect entanglement without
the need for costly state tomography as illustrated for a variety of physically
relevant states (Gaussian, mixed Schr\"odinger cat, and NOON states). The
influence of typical experimental imperfections is shown to be moderate.
