The photograph below shows a mating pair of Tachypleus tridentatus (Chinese horseshoe crab), caught in a fisherman’s net in the mouth of a stream at Ha Pak Nai, Deep Bay, Hong Kong on 15 September 2009.
The female on the left of the picture is 35 centimetres across the head shield. The smaller male is 25 cms across.
In the late 1960’s this fisherman once caught 200 Chinese horseshoe crabs in a single night and in the 1960's and 1970's such large catches of horseshoe crabs were not uncommon at Ha Pak Nai. In 2009 he caught just this one mating pair.
Undisturbed streams, particularly in their lower reaches are critical to horseshoe crab ecology in Hong Kong, because horseshoe crabs use stream courses to navigate across beaches and both T. tridentatus and C. rotundicauda have been observed to spawn in the lower reaches of streams in Hong Kong.