Fish reef - Gyosho

A raised part of the seabed that becomes a good fishing ground where fish gather. If fishing is conducted there, it is also written as a fishing reef. Depending on its shape, area, depth, and bottom quality, it is called a reef, bank, shoal, or shallows. Around the reef, rising and falling currents occur along the topography, and the circulation of seawater becomes active, carrying nutrients from the deep water to the upper layer where sunlight penetrates. As a result, plankton proliferates in the upper layer, attracting small fish that feed on it, and larger fish then gather to prey on it, resulting in the formation of a good fishing ground. In addition, the complex structure of a fish reef is suitable for fish to protect themselves from predators, and the whirlpools that form around the reef make it easy for fish to remain there, which are also factors that make it a good fishing ground. Depending on their origin, fish reefs are classified into volcanic reefs, structural reefs, and coral reefs. There are many fish reefs that serve as good fishing grounds in the seas off Japan, but the Yamato and Musashi banks in the Sea of ​​Japan, and the Soyo, Koho and Kounan banks on the Pacific coast are particularly distinctive, with shallow waters that jut out from the seabed at a depth of more than 3,000 meters to a few hundred meters below sea level, making them good fishing grounds for fishing and longlining, where migratory and bottom-dwelling fish can be caught. In addition, Omuro-dashi, Zenisu and Kurose off the coast of Izu are known as spawning grounds for Pacific schools of chub mackerel, and small islands such as Nishinoshima, Aogashima, Torishima, Takarajima, Akusekijima, Hachijo-kojima and the Bayonnaise Rocks also function as fish reefs, providing fishing grounds for island-attached schools of fish. Additionally, seamounts that protrude from the deep seafloor have also become known to be valuable fishing grounds, and many years of research have revealed that the spawning grounds of Japanese eels are near Suruga Seamount off the coast of the Mariana Islands.

Taking advantage of the tendency of fish to gather around reefs, people have been creating artificial reefs to catch fish efficiently since ancient times, and have used sunken abandoned ships, rocks, sumo rings, and old vehicles such as buses and trains as reefs. Since 1954, the construction of artificial reefs has been subsidized by the government, and concrete blocks and other materials have been used as reefs. Furthermore, research has progressed on lightweight, wave-resistant materials for reefs, and shapes that attract fish, and the scale of reefs being used has been increasing year by year.

[Kiyoshi Yoshiwara]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

海底の隆起部で、魚類が集まって好漁場となる場所。そこで漁業が行われている場合は漁礁とも表記される。その形、広さ、水深、底質により岩礁、堆(たい)、州(す)、瀬(せ)などとよばれる。魚礁付近は、地形に沿って上昇流や下降流が生じて海水の循環が活発となり、深層の栄養塩類が日光の透入する上層まで運ばれる。そのため、上層はプランクトンの繁殖が旺盛(おうせい)となり、これを餌料(じりょう)とする小魚が集まり、さらにそれをねらって大形魚が集まるようになり、結果として好漁場が形成される。また魚礁はその複雑な構造が魚類が外敵から身を守るのに適しており、さらに魚礁の周りは渦流が生じるので、魚類が滞留しやすいことなども、好漁場の要素としてあげられる。魚礁は、その成因により火山性魚礁、構造性魚礁、サンゴ礁に分類される。日本近海には好漁場となる魚礁が多く存在するが、なかでも日本海の大和(やまと)堆、武蔵(むさし)堆、太平洋側の蒼鷹(そうよう)堆、高鵬(こうほう)堆、紅南(こうなん)堆などは特色があり、水深3000メートル以上の海底から海面下数百メートルに突き出た浅瀬で、釣りや延縄(はえなわ)などの好漁場として回遊魚や底生魚が漁獲される。また、伊豆沖の大室(おおむろ)出し、銭州(ぜにす)、黒瀬などはマサバ太平洋系群の産卵場として知られ、西之島、青ヶ島、鳥島、宝島、悪石島(あくせきじま)、八丈小島、ベヨネーズ列岩などの小島嶼(とうしょ)も魚礁の役割を果たしており、これらは島つき魚群の漁場となる。また、深海底から突出している海山(かいざん)も漁場的価値が知られるようになり、ニホンウナギの産卵場所が、マリアナ諸島沖のスルガ海山付近であることが、長年の研究で明らかになった。

　魚礁に魚が集まる性質を利用して人工魚礁をつくり、効率よく魚をとることは古くから行われており、廃船を沈めたり、岩石、土俵、バスや電車などの老朽車両を魚礁として投入していた。1954年（昭和29）から人工魚礁設置事業が国の補助の対象となり、コンクリートブロックなどを魚礁として投入している。さらに、軽量で耐波抵抗のある魚礁の材質や、魚の集まりやすい形状の研究も進み、投入規模も年々大型化している。

［吉原喜好］

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