Simplified quantification method of the population of benthic animals with hole on a mud tidal flat by digital processing aerial photos

Abstract

We attempted to determine the distribution of benthic animals and to quantify their population densities focusing on the life traces on a tidal flat. By processing digital photos taken from a radio controlled helicopter equipped with geographical positioning system, distribution of nest holes on the tidal flat of Imazu was obtained with the thirtieth effort of manual surveying on site. Benthic animals that build nests on tidal flat of Sone, Fukuoka prefecture represent about 50 per cent of population on the tidal flat, among them shrimps and crabs represent about 8 per cent. On the area where the percentage of clay and silt exceed 50 per cent, shrimps and crabs represent 28 per cent by wet weight. Distribution of a mud crab (Yamato osagani: Macrophthalmus japonicus) was identified by the distribution of the holes they make.