Current status of Tachypleus tridentatus in Taiwan for red list assessment

Abstract

The horseshoe crab, Tachypleus tridentatus, once thrived on the west coast of Taiwan as evidenced by history, literature, colloquial language, daily usage and places named after it. After more than 15 years of efforts to conserve its populations, the horseshoe crab population remains threatened. A study on juvenile density changes in the Guningtou Horseshoe Crab Conservation Area in Kinmen Island showed that over 7 years from 2003 to 2009, the juvenile population declined rapidly from 0.30 individuals/m 2 in 2003 to between 0.02 and 0.17 individuals/m 2 in 2004–2009. Adult population surveys and scattered landing reports on fi shing wharfs produced only about several tens individual catches at the most, implying a very limited adult distribution in waters surrounding Taiwan. The threats to T. tridentatus in Taiwan include habitat loss, habitat deterioration due to armored shorelines, pollution, Spartina invasion and human consumption. Conservation actions implemented include: habitat protection and improvement, population enhancement, education, and listing the horseshoe crab as a protected species. We now recommend designating new protected areas on the western and northeastern coasts of Kinmen Island as our studies show that these coasts possess beaches with the highest potential for spawning. We also strongly suggest that instars up to the third instar stage are appropriate for release, because they survive better in the field.