Dust velocity as a function of distance from the star and dust Stokes number in a disc hosting a 100 M_⊕ planet that has carved a gap at 10 au (upper panel) compared to a smooth disc (lower panel) for a global viscosity α_visc = 10⁻³ and local turbulence δ_turb = 3.2 × 10⁻⁴. Negative velocity represents the inwards motion of dust grains (red) while a positive velocity shows the outwards motion (blue). The dark contours represent the variations in Stokes number for fixed particle size (from 1 μm to 1 mm). The Stokes number decreases monotonously in the smooth disc when approaching the star. In planet-hosting discs, low gas density in the planetary gap increases the Stokes number locally.