Preliminary home range study of juvenile Chinese horseshoe crabs, Tachypleus tridentatus (Xiphosura), using passive tracking methods

Abstract

Three passive tracking methods, using colored plastic tag (CPT), passive integrated transponder (PIT) tag, and CPT plus PIT were compared to track the movements of juvenile Chinese horseshoe crabs, Tachypleus tridentatus, in summer 2013 on a mudflat in Hong Kong. The study site was re-visited within 2 months after the release of the tagged individuals on ten occasions during low tides. The cumulative recovery rates of the tagged juveniles ranged from 70 to 82 #x0025;, with the number of position fixes where each individual was recovered during the repeated field visits varying from one to seven. Based on the adaptive kernel density estimation approach, the mean home range size (indicated by 95 #x0025; utilization distribution) tracked by different methods varied between 269 and 462 m2. While the effects of tracking methods on home range size of the juveniles were statistically indistinguishable, PIT tags could be used as a longer-term tracking device for juvenile horseshoe crabs because the tag injected into animal bodies did not cause noticeable effects on survival, growth and molting. Within the body size range of 7th–10th instar juveniles (prosomal width 31–59 mm) used in the present study, no significant correlation was found between body size and home range area. From the analysis of utilization distribution, the juveniles were noted to exhibit residential and nomadic movement patterns, which might be associated with the distribution of food patches on the mudflat. The restricted movements of juveniles in this study suggest potential for high susceptibility to localized habitat disturbance.