  Previously published experimental work by other authors has shown that
certain motile marine bacteria are able to track free swimming algae by
executing a zigzag path and steering toward the algae at each turn. Here, we
propose that the apparent steering behaviour could be a hydrodynamic effect,
whereby an algal cell's vorticity and strain-rate fields rotate a pursuing
bacterial cell in the appropriate direction. Using simplified models for the
bacterial and algal cells, we numerically compute the trajectory of a bacterial
cell and demonstrate the plausibility of this hypothesis.
