OYSTER RUBBLE REDUCES THE HOME RANGE AND DISTURBS THE FORAGING BEHAVIOUR IN TACHYPLEUS TRIDENTATUS

The home range of the juvenile Chinese horseshoe crab Tachypleus tridentatus was determined at Ha Pak Nai, where the highest density of this animal was found in Hong Kong. The movement pattern of juvenile T. tridentatus was tracked using the coloured plastic tag (CPT) during low tides in the summer of 2018. The survey lasted for 2 months with 130 individuals being tagged. The mean recovery rate of tagged individuals was 44%. The positional fix for each recaptured individual was recorded during each survey and the size of the home range was estimated using the minimum convex polygon (MCP) of the ArcGIS. Ha Pak Nai was divided into regions with high (≥ 1 oyster shell m^-1) or low density of oyster rubble (< 1 oyster shell m^-1). Eightyeight percentage of the juvenile horseshoe crabs preferred utilizing the region with less oyster rubble and the home range was also statistically larger (median: 55.75 m²) as compared with the area with more oyster rubbles (median: 88.9 m²). The juveniles were also found to prefer foraging during sunny days than drizzling days, and on the sediment covered with a thin layer of water than deeper puddles. Conservation issues related to the findings are discussed.