In rotating duct flows, coherent longitudinal vortical structures develop even for very low Reynolds numbers due to the shear-Coriolis instability, where the mean absolute vorticity is close to zero. We investigate the creation mechanism of zero-mean-absolute-vorticity region focusing on the role of the longitudinal vortical structures for the plane-Poiseuille- and plane-Couette-type flows with the system rotation. It is found that the way of the vortex tubes to create zero-mean-absolute-vorticity state is different between the two cases. For the rotating plane-Poiseuille-type flow, the generated longitudinal vortex tubes develop the spanwise vorticity around them, whereas for the rotating plane-Couette-type flow, they enhance the spanwise vorticity inside them. However, it is common for the two cases that zero-mean-absolute-vorticity state is created by the action of the coherent longitudinal vortices in the anticyclonic region. 2006 Springer.