Annual life cycle and distribution of adult gurnard Lepidotrigla microptera in Mutsu bay, Aomori prefecture [Japan]

The annual life cycle and distribution of adult Lepidotrigla microptera were studied in the Mutsu Bay, Aomori Prefecture. The seasonal changes in gonadosomatic index, hepatosomatic index, condition factor, and stomach contents index of samples obtained by experimental bottom trawls from March 1986 to July 1988 indicated that the annual life cycle of adult L.microptera was divided into the following four periods; wintering period (December-March), preparatory period for spawning (April-May), spawning period (June-August), and preparatory period for wintering (September-November). The habitat of L. microptera in this study area was not confirmed. However, at least a part of them were concentrated in relatively warm waters (6-9°C), i.e. the mouth of the bay in winter. In spring, most of them moved to the western part of the bay (West Bay) with rising bottom water temperature. In summer their habitat spread over the bay, and the fish concentrated toward the mouth of the bay in autumn. The annual life cycle and the space utilization pattern of adult L. microptera are thus associated greatly with seasonal changes in the bottom temperature.