群馬県赤城大沼で見つかったカラスガイ属幼貝の貝殻

Abstract

2024年8月に群馬県赤城山大沼の湖岸でカラスガイ属の貝殻が複数個体みつかった。殻長3–6cm程度の幼貝も含まれ，この湖での近年の繁殖が示唆された。大沼の個体群は過去のセタシジミやワカサギの移入に伴うと考えられる移植集団で，群馬県では国内移入種であるが，全国的にカラスガイ属は絶滅に瀕しており，群馬県内での本種の繁殖の情報は少ないため記録した。また付録として大沼周辺に生息する魚類をまとめた。

In August 2024, several cockscomb pearl mussel (Cristaria sp.) shells were found on the shore of a lake in the Onuma area of Akagi Mountain, Gunma Prefecture. The shells contained juvenile clams with shell lengths of 3–6 cm, suggesting that they had recently reproduced in the lake. The Onuma population is a transplanted population of a species that was introduced to Gunma Prefecture in the past through the basket clam (Corbicula sandai) and Japanese pond smelt (Hypomesus nipponensis) invasions. The freshwater mussel is an endangered species, and there is little information on its breeding in Gunma Prefecture, so we report it here. In addition, fish species inhabiting the Lake Onuma area are summarized in the appendix.