Radiative decay from the excited P-1(1) state to metastable P-3(2) and P-3(0) states is expected to limit the attainable trapped atomic population in a magneto-optic trap of ytterbium (Yb) atoms. In experiments we have carried out with optical repumping of P-3(0,2) states to P-3(1), we observe an enhanced yield of trapped atoms in the excited P-1(1) state. The individual decay rate to each metastable state is measured and the results show excellent agreement with the theoretical values.