  In strong magnetic fields the transport coefficients of strange quark matter
become anisotropic. We determine the general form of the complete set of
transport coefficients in the presence of a strong magnetic field. By using a
local linear response method, we calculate explicitly the bulk viscosities
$\zperp$ and $\zpara$ transverse and parallel to the $B$-field respectively,
which arise due to the non-leptonic weak processes $u+s\leftrightarrow u+d$. We
find that for magnetic fields $B<10^{17}$ G, the dependence of $\zperp$ and
$\zpara$ on the field is weak, and they can be approximated by the bulk
viscosity for zero magnetic field. For fields $B>10^{18}$ G, the dependence of
both $\zperp$ and $\zpara$ on the field is strong, and they exhibit de Haas-van
Alphen-type oscillations. With increasing magnetic field, the amplitude of
these oscillations increases, which eventually leads to negative $\zperp$ in
some regions of parameter space. We show that the change of sign of $\zperp$
signals a hydrodynamic instability. As an application, we discuss the effects
of the new bulk viscosities on the r-mode instability in rotating strange quark
stars. We find that the instability region in strange quark stars is affected
when the magnetic fields exceeds the value $B= 10^{17}$ G. For fields which are
larger by an order of magnitude, the instability region is significantly
enlarged, making magnetized strange stars more susceptible to $r$-mode
instability than their unmagnetized counterparts.
