  Advection properties of passive particles in flows generated by point
vortices are considered. Transport properties are anomalous with characteristic
transport exponent $\mu \sim 1.5$. This behavior is linked back to the presence
of coherent fractal structures within the flow. A fractional kinetic analysis
allows to link the characteristic transport exponent $\mu $ to the trapping
time exponent $\gamma =1+\mu $. The quantitative agreement is found for
different systems of vortices investigated and a clear signature is obtained of
the fractional nature of transport in these flows.
