有明海湾奥部干潟におけるトビハゼ （Periophthalmus modestus）の月間分布変動について

抄録

We demonstrate monthly changes in the distribution of a population of the mudskipper Periophthalmus modestus inhabiting a mud bank of the Fukushoe River, flowing into the Ariake Sea, Japan. During the reproductive season from June to midAugust, fish density observed on the surface during lowest spring tide decreased from the most landward quadrats toward the river channel, particularly where the bank inclination was steep (within 30 m from the water’s edge). Males accounted for over 90% of individuals collected at the most landward sampling plot, 67 to 15% at the next three plots, and 0% at the most riverward plot, where only females were collected. During the non-reproductive season from September to November, fish density also decreased toward the river channel, with no fish confirmed at the river’s edge. Although the percentage of males decreased from landward to riverward plots, the trend was less marked than during the reproductive season. Monthly sampling of fish on riprap at the time of highest spring tide showed females to be dominant (70–90% of total) from May to July, with juveniles appearing in July and becoming dominant (70–80%) in August to October. No fish occurred on the riprap from November to the end of January. These findings suggest that many females migrate with the tide for feeding at the water’s edge, thereby achieving rapid ovarian development, whereas mature males remain near their territory and burrows. Reproductive burrows were most abundant in the area of stable daily periods of submersion and emersion (300 min and 400–500 min, respectively) throughout the tidal cycle, suggesting that a regular cycle of inundation and emersion is important for the successful reproduction of the species.