Sex Ratio In The Population Of The Ghost Shrimp, Nihonotrypaea Japonica (Ortmann, 1891) (Decapoda: Thalassinidea: Callianassidae), Collected From Shirakawa River, Central Part Of Ariake Sound, Western Kyushu, Japan

Abstract

The present study was carried out on an intertidal sandflat developed at the mouth of Shirakawa River, central part of Ariake Sound, western Kyushu, Japan. The aim of the present study is to discuss the sex ratio in the population of Nihonotrypaea japonica from biological point of view. Sampling of the N. japonica population was conducted on a total of 21 occasions (spring tides) during the period from 20 April 1999 to 18 April 2000. With regards to the sampling interval, the study period can be grouped into 2 parts: (1) during 20 April – 22 November 1999, every 2 weeks, and (2) during 22 December 1999 – 18 April 2000, once a month. Sample collections were made by means of ‘yabby pumps’ during low tide on each occasion. The collected samples consist of 5628 females, 4385 males, and 346 sex-unidentified individuals, giving a female-biased sex ratio for the entire population. However, by dividing into several classes, there was a pattern of sex ratio, which seems to be related to reproductive aspect of the shrimp.