  We study longitudinal transport in Weyl semimetal nanowires, both in the
absence and in the presence of a magnetic flux threading the nanowires. We
identify two qualitatively different regimes of transport with respect to the
chemical potential in the nanowires. In the "surface regime", for low doping,
most of the conductance occurs through the Fermi-arc surface states, and it
rises in steps of one quantum of conductance as a function of the chemical
potential; furthermore, with varying flux the conductance changes in steps of
one quantum of conductance with characteristic Fabry-P\'erot interference
oscillations. In the "bulk-surface regime", for highly-doped samples, the
dominant contribution to the conductance is quadratic in the chemical
potential, and mostly conditioned by the bulk states; the flux dependence shows
clearly that both the surface and the bulk states contribute. The two
aforementioned regimes prove that the contribution of the Fermi-arc surface
states is salient and, therefore, crucial for understanding transport
properties of finite-size Weyl semimetal systems. Last but not least, we
demonstrate that both regimes are robust to disorder.
