Distribution and abundance of two sympatric species of horseshoe crabs along the Odisha Coast, India

Abstract

Two sympatric species of horseshoe crab Tachypleus gigas and Carcinoscorpius rotundicauda are found along the coastlines of Odisha, India facing the Bay of Bengal. The distribution and abundance of these two species were surveyed for a period of 1 year from two coastal sites at Ekakula and Balaramgadi of Odisha in link with phases of the moon. At Ekakula, both species were encountered during the study period; however, over 95 #x0025; of the horseshoe crabs recorded were dead. While the numbers of horseshoe crabs counted during new and full moon phases were statistically similar for both species, relatively fewer sightings were recorded in the winter period. Combining all live and dead specimens, a higher mean density of 1.34 individuals/m2 was recorded for T. gigas than that of 0.18 individuals/m2 for C. rotundicauda. In addition, a clear habitat preference was noted, in which T. gigas was found on sandy beaches whereas C. rotundicauda near mangrove fringes. At Balaramgadi, only sightings of dead T. gigas were encountered, and abundance was found to be very low, ranging from zero to four specimens per sampling occasion. At both sites, survival of horseshoe crabs was severely affected because of entanglement of individuals in various types of nets along the shore due to intense fishing activities. Threats that persist to horseshoe crab populations on Odisha coast also included high predation pressure from wild animals and loss of spawning ground due to coastal developments. Establishment of routine monitoring programmes and conservation reserves and training of enforcement agencies to protect horseshoe crab populations in India are proposed.