島根の水辺の生きもの：池と河川
島根の池と河川は、広くゆっくりと流れる三角州から流れの早い上流や山間部の小川まで、多種多様な動物たちの住処となっている。池や大きな河川の静かな水面にはオイカワやミナミメダカなどの魚や、それらを餌とするアオサギやカワセミなどが住んでいる。カワセミはその名に反して金属的な青緑色の羽がヒスイを連想させる。日本語名にはその特性が反映され、翡翠（ヒスイ）という漢字はカワセミとも読まれる。
冷たくて流れが激しい島根県の川の上流には主に島根県と岡山県に見られるゴギが棲む。これらの水辺はオオサンショウウオという不思議な見た目の生物の棲家でもある。オオサンショウウオは世界最大級の両生類で体長は最大 1.5 メートルにもなる。オオサンショウウオはえらがなく、皮膚呼吸をするために酸素が循環する流れの早い水辺が拠り所だ。魚や甲殻類を常食とし、水中で獲物の振動を感じてすばやく捕獲する。水辺の護岸に穴を掘って巣をつくるヤマセミもまた川魚を捕獲する。原因は不明だが、ここ数十年のうちに、島根県のカワセミの数が危険なほどに減っている。
Life Along the Water’s Edge: Ponds and Rivers
Shimane’s ponds and rivers, which vary from broad, slow-moving river deltas to the fast-moving upper reaches of rivers and mountain streams, are home to many different species of animals. The still waters of ponds and larger rivers are inhabited by fish such as the freshwater minnow and Japanese rice fish, as well as the birds that prey upon them, such as the grey heron and common kingfisher. In spite of its name, the common kingfisher is an impressive bird whose metallic turquoise plumage is reminiscent of a blue-green jewel—a trait that is reflected in the bird’s Japanese name, which is written using the characters for “jade.”
The cold, swift-flowing upper stretches of Shimane’s rivers are inhabited by a type of whitespotted char found mainly in Shimane and Okayama prefectures. Those same waters are also home to a more intimidating resident: the Japanese giant salamander. The giant salamander is one of the world’s largest amphibians and reaches up to 1.5 meters in length. Lacking gills, the giant salamander relies upon fast-moving water to circulate oxygen across its absorbent skin folds. Its diet consists of fish and crustaceans, which it senses through vibrations in the water and snatches at great speed. Another predator of river fish is the crested kingfisher, which nests in the holes it excavates in waterside embankments. In recent decades, unknown causes have led to an alarming drop in the number of crested kingfishers in Shimane.
