The population size and movement of coastal horseshoe crab, Tachypleus gigas (Müller) on the East Coast of Peninsular Malaysia

Abstract

Horseshoe crabs have recently gained popularity as new exotic delicacies in Malaysia, especially in Johor. It has been reported and claimed by some fishermen that horseshoe crabs, particularly females, are being transported in bulk to Thailand. This claim has sparked interest to identify population size and study the behaviour of horseshoe crabs along the east coast of Peninsular Malaysia in an attempt to determine the effect of this demand on the existing population. A study was carried out from December 2011 to March 2012 to determine the coastal horseshoe crab Tachypleus gigas population size in Chendor and Cherating, Pahang, about 10 km apart on the east coast of Peninsular Malaysia, using a Capture-Mark-Recapture method. The sampling was carried out three times at both sites. The population size was calculated using Bailey's Triple Catch formula with the assumption of an open population. The horseshoe crabs' ‘traveling distance’ was also determined by attaching numbered, white button tags, each bearing the researcher's phone number, to a total of 99 horseshoe crab individuals (61 in Chendor, 38 in Cherating). The total estimated populations were 7,140 in Chendor and 9,900 in Cherating. The two populations were found to be interchangeable as the tagged animals from Chendor were recaptured in Cherating and vice versa, thus confirming emigration and immigration. About 25 #x0025; of tagged animals were recaptured in various places (at Chendor, Cherating and also outside both locations) as reported by fishermen. Animals tagged in Cherating were caught in a few locations in Pahang, including Tanjung Lumpur which is more than 50 km to the south. Most recaptures (40 #x0025;) were from different locations remote from the site where the horseshoe crabs were tagged and released. This study is on-going and notifications are still expected regarding the future location of the tagged animals.