Fig. 1. The peg-board system used to erect different configurations of walls. (A) Grooves were cut into the acrylic base plate so that supports could be positioned. Grey lines on base indicate scratched surface for traction. (B) Walls were attached by a clip at the top. Spacers were placed between the support and wall in the laneway configuration to standardise the width to 65 mm. (C) An example of one of the configurations of walls (straight) during a trial. Cameras were fixed to a tripod and suspended over a wall. Two cameras with overlapping fields were used over long walls, as shown. Footage was previewed on a monitor and recorded on video cassette recorder (VCR). Weights held the base plate to the bottom of the large tank (not shown). (D) Plan views of the five wall arrangements for the two experiments. Configurations are, from top to bottom: straight wall middle release (1), straight wall end release (2), corner (3), square (4) and laneway (5). Crayfish are shown in the release chamber, as they were positioned prior to a trial. The open and closed positions of the chamber in the end wall configuration are shown. End line and outer limit of observation zones that determined wall following are marked with dotted rectangles.