氣候變異對日本鰻苗捕獲量減少之探討

Abstract

本研究利用衛星觀測和同化模式資料探討在東亞區域日本鰻(Anguilla japonica)鰻苗捕獲量之變化。研究發現當西北太平洋區域的鹽度鋒面極端的往南移，會造成日本鰻的產卵場也會跟著異常地往低緯度移動，導致東亞區域的捕獲量在1983、1992和1998有大量減少的現象。進一步發現此現象並不是完全由聖嬰現象所造成，且並不是強聖嬰事件就會發生，例如2015/16的強聖嬰事件就沒有發生鹽度鋒面極端的往南移和鰻苗大量減少的現象。然而，這些極端的事件與氣候組合模態(Combination mode，簡稱C-mode)有很好的相關性。結果顯示因為受到C-mode氣候變化的影響，改變了西北太平洋的降雨型態，也導致鹽度鋒面極端的往南移動，進而造成日本鰻魚產卵場往南移動，不利於鰻苗隨著海流(北赤道洋流-黑潮系統)傳輸到東亞區域，進而嚴重地影響到東亞國家的鰻苗捕獲量。最後本研究提出藉由海表溫(sea surface temperature)的變化做為預測指標，可以幫助提前預測鰻苗在東亞區域的捕獲量。Satellite data and assimilation products are used to investigate fluctuations in the catch of Japanese glass eel (Anguilla japonica) in eastern Asian countries. It has been reported that the salinity front has extended farther south, which has shifted the eel’s spawning grounds to a lower latitude, resulting in lower glass eel catches in 1983, 1992, and 1998. Interannual variability in the glass eel catch is strongly correlated with the combination mode (C-mode), but not with the El Niño–Southern Oscillation or supper El Niño events. For example, the 2015/15 El Niño events is a super El Niño events, but it did not result in extremely poor recruitment of Japanese eel in East Asia. The spawning grounds accompanied by the salinity front extend farther south during the C-mode of climate variability, and eel larvae fail to join the nursery in the North Equatorial Current (NEC) and Kuroshio, resulting in poor recruitment in East Asia. We have proposed an appropriate sea surface temperature index to predict Japanese eel larval catch in the East Asia area.