59 巻 (2004) p. 8-12
Occurrences of rare species of fiddler crab, Uca arcuata (De Haan, 1833) and U. lactea (Dc Haan, 1835), are newly recorded from a tidal flat at the mouth of the Aono River, Izu Peninsula, Shizuoka Prefecture, Japan. Numbers of crabs and their sexes were recorded by viewing from a distance, and several of the crabs were collected for measuring their size. Observations and sampling were conducted 12 times from September, 1999, to August, 2002, at low spring tide. During this period, three individuals of U. arcuata were recorded, all males. Numerous individuals of UU lactea were found during the same period, and the maximum number recorded was 36 in September, 2000. Ages of the crabs were estimated from carapace size, based on earlier published population studies. The largest male U. arcuata on the Aono River flat was estimated to be two years old, and the other two males were one year old. Collected males of U. lactea ranged from 15.8 to 18.5mm in carapace width, and females from 13.3 to 15.8mm; the ages of these crabs were estimated as two years or more.