Abstract
A preliminary study of the effectiveness of an infrared monitoring system to detect the timing of exit and re-entry to a hole used as a daytime refuge by an individual juvenile P. japonicus was carried out at the Kominato Marine Biosystems Research Center of Chiba University. The monitoring system consisted of the infrared beam source and sensor which were attached to either side of the hole and connected by a 5 m cable to an external exchangeable battery and data logger. For a six day period (25th September to 1st October, 1998) clear activity patterns were observed for an individual lobster (ca. 120 mm total length) showing that the nocturnal foraging pattern of the individual lobster had a high degree of variation in both the duration of foraging (between ca. 1 to 4 hrs) and the period remaining in the hole during the night. The sensor showed high levels of response especially around dusk and dawn when we conclude that the lobster was near to the entrance of the hole and also intermittent peaks during the night when the lobster emerged to forage and then returned. In summary, the lobster remained in its hole during the day and moved to the entrance of the hole at dusk observed before emerging to forage and then returned to the hole at intermittent periods during the night. We conclude that the possession of a suitable hole and its defense from conspecifics may be a key factor, along with prey availability, determining the duration of foraging behavior and that the infrared system is highly effective for monitoring the movement patterns of juvenile lobsters.
