Endangered crayfish in northern Japan: Distribution, abundance and microhabitat specificity in relation to stream and riparian environment Original Research Article

Japan’s only native crayfish species Cambaroides japonicus has been declining dramatically in the past few decades. For the purpose of conservation planning, twenty-two coastal streams were surveyed to investigate summer distributions of crayfish in relation to stream and riparian environment. Classification and regression trees were used to predict the occurrence and abundance of crayfish. The classification tree model with stream variables as predictors showed that crayfish would occur in swift or high gradient streams (correct classification rate = 91%). Within those streams, however, crayfish only inhabited depositional microhabitats, in which the areas are limited in availability. Crayfish were not found in gentle, low gradient streams containing abundant depositional microhabitats. This paradoxical distribution pattern was attributed to availability of boulder substrates in swift or high gradient streams. The regression tree model indicated that crayfish abundance was determined primarily by the percentage of boulder substrates and the presence of fish (observed vs. predicted r = 0.64).