Traps employed to catch crustaceans are usually set before sunset and collected after dawn, so that the time they spend in the fishing ground (soaking time) coincides with the active phase of the target species. Swimming crabs are mostly nocturnal, though they also show short periods of activity during the day, and as a result have to rely mostly on their senses of smell and taste to find food or prey.
The capture process of an aquatic animal approaching a trap has been summarized as consisting of several behavioral stages (Furevik 1994), which start with distant detection, and continue with approach, contact, near ingress behavior, sometimes entry, and end with capture and/or escape. The first two, detection and approach are mediated by the sense of smell of the organism and are influenced by the distribution of the odor emanating from the trap as the current carries it downstream. Fishers can place bait or live crab decoys in their traps to attract other crabs towards them. I will discuss the lures they employ in the following sections.
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