In the present study, the sea cucumber dredge area in Ohmura Bay, Nagasaki Prefecture (off the Fisheries Cooperative of Ohmura Bay) were partitioned in 10 seconds lat/long mesh and still images of 37 site covering the entire area were taken. The sea bottom substrate material and the density of gravel (>6.4×10^<-2>m in diameter) were then calculated from the images. The relationship between bottom sediment and the sea cucumber catch was then investigated from the number (individual/ha: CPUE[Ind.]) of sea cucumber caught per unit of the dredged area from 81 times of dredging by the sampling ship. Most part of the operation was conducted on S sea bottom. A negative correlation was found between the average gravel density and the CPUE[W] (n=162, r=-0.29, p<0.01) but the CPUE[Ind.] was diphasic distribution, exhibiting peak at 0 and 9 average gravel densities (number/m^2). From these results, gravel density is not only important factor that changes the Catchability of sea cucumber dredge, but also time changes the individual size and habitat density.
