Fig. 6. Average search time (±S.E.M.) required for successful whelks to navigate from the starting cage to the odor source located 1.5 m upstream. (A) Compared with search times in the slowest unobstructed flow, knobbed whelks tracked more efficiently (i.e. reduced search time) in the two fastest flows. Seven tracks were analyzed for each of the unobstructed treatments and asterisks indicate a significant reduction in search time compared with the 1.5 cm s^–1 treatment (P<0.05). (B) Compared with search times in unobstructed flow of the same velocity, knobbed whelks tracked more efficiently when the cylinder obstruction introduced turbulent mixing at the odor source. Five tracks were analyzed for each of the obstruction treatments and asterisks indicate a significant reduction in search time compared with the unobstructed (smooth) condition (P<0.05).