Fig. 1. Flow tank schematic. Seawater was first piped into a tilted inflow tank (95 cm wide, not shown), passing over or under four barriers, before spilling into the flow tank across its full width (black arrows). Flow continued through a 0.75 cm thick Plexiglas baffle (bf) drilled with 0.75 cm holes, two upstream grilles (ug1 and ug2; 1 cm square mesh, 0.75 cm thick), a behavioural arena (ba), and a downstream grille (dg) to prevent slugs being swept out of the tank, before spilling over the downstream end wall (cut 2 cm lower than the other tank walls). Plexiglas walls spanning the gap between the upstream grilles created an odour stimulus chamber (osc). This design created unidirectional flow through the behavioural arena with enough turbulence to spread fluorescein dye plumes (grey approximates the average plume shape) similarly to plumes in the field (Wyeth and Willows, in press). Odor plumes will be similar to these dye plumes since flow dominates chemical transport under such conditions (Vogel, 1994). The 2nd upstream grille also served to obscure any downstream flow patterns characteristic of the odour sources (Vogel, 1994). Flow tank width, 1 m.