Elucidation of recruitment mechanisms of Japanese eel based on 30 years monitoring glass eel recruitment and early life history analysis

2021 Fiscal Year Final Research Report

• Project/Area Number: 16K07853
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Aquatic bioproduction science
• Research Institution: Tokyo Medical University
• Principal Investigator: Shinoda Akira 東京医科大学, 医学部, 准教授 (70401297)
• Project Period (FY): 2016-04-01 – 2022-03-31
• Keywords: ニホンウナギ / シラスウナギ / 初期生活史 / 接岸回遊 / 耳石

Outline of Final Research Achievements

In recent years, Japanese eels have been decreasing in the amount of recruitments, although the cause of this decrease is not clear. We conducted a monitoring glass eel recruitment on Tanegashima Island, Kagoshima Prefecture, from 2016 to 2022, and analyzed the recruitment mechanisms of Japanese eels in conjunction with data from 1991. It was suggested that fluctuations in the timing and amount of recruitment at Tanegashima cannot be explained simply by environmental changes in the open ocean, such as El Nino/La Nina events, but are influenced by eddies in the coastal zone. Early life history analysis of glass eel showed a trend of reducing total length and increasing larval migration period in the ocean with each successive generation. The reduced total length and increased duration of larval migration negatively affect the survival of larvae in the ocean and lead to a decrease in the amount of recruitment.

Free Research Field

魚類生態学

Academic Significance and Societal Importance of the Research Achievements

シラスウナギ漁獲量の年変動が生じる要因は明らかではない。鹿児島県種子島において、1991年から30年の長期にわたるタイムスパンでニホンウナギの接岸回遊機構を解析した。種子島の接岸時期や接岸量の変動は、外洋の環境変化だけでは説明できず、沿岸域の渦などの影響を受けることが示唆された。これは将来の漁獲量予測のための基礎知見となる。初期生活史解析からは、世代を経るごとに全長の縮小傾向と海洋での輸送期間の増加傾向が認められた。これはニホンウナギの3世代にあたる30年の解析を行った結果である。これまで知見のなかった降河回遊魚の初期生活史の数十年単位の環境応答について重要な基礎的情報が得られた。