Behavior of the Commercial Sand Crab Portunus pelagicus (L.) at Trap Entrances

Abstract

Time lapse video recordings were used to study the trap entrance behavior of the sand crab (Portunus pelogicus L.) in the laboratory. The trap used was cylindrical with two opposite entrance funnels, as commonly used in the Australian commercial fishery. Crabs usually made several entrance attempts (i • 2), and 66% and 72% of males and females, respectively, searched less than one-quarter of the trap circumference before entry. It was not uncommon for sand crabs to miss the entrances: for crabs that made an entrance attempt, males missed funnels an average of 2.2 times as compared to females 1.7 times. Entry success rates were 30% and 25% for males and females, respectively, although there was no significant difference in the number of entries between the sexes. Entry order into the baited trap by sex or size was not significant. Antagonistic interactions rarely prevented a crab from entering the trap, but occasionally (<5% of entries} trapped crabs inside the trap prevented newcomers from entering the trap. Crabs also occasionally backed out of a funnel for no apparent reason. The trap was not considered efficient at catching crabs. A more efficient trap would require more entrance space presented to an approaching crab.