Conservation study focusing on habitat use in darter (meadowhawk) populations that used to flourish in the rice paddy fields of Japan

Recent decreases in population size of some Sympetrum species (Odonata: Libellulidae) that used to flourish in paddy fields in Satoyama, Japan, are thought to be caused by the development of rice cropping systems. As habitat use is species-specific, some conservation studies have shown that the causes of the decline in darter populations may also be species-specific. While eggs and larvae of lentic species like Sympetrum frequens decrease owing to the effect of pesticides, those of S. pedemontanum elatum, which lives along weakly flowing water, are not influenced by these chemicals, although they have decreased with the modernization of water management in paddy fields. It is also known that drying of the soil surface in no-till farming areas does not reduce the population size of S. infuscatum, whose eggs have a higher resistance to drought than those of other darter species. For the conservation of darters, we should investigate habitat use during the developmental stages of each species, identify the causes of population decline, and maintain a suitable balance within the microhabitats required by each darter species. Such designed habitats will contribute to the conservation of not only darters, but also many other aquatic organisms endangered in the paddy fields of Satoyama.