The Temporal and Spatial Change in Position of Squid Fishing Ground in Relation to Oceanic Features in the Northeastern Waters of Taiwan

Abstract

本研究利用地理資訊系統，將衛星遙測所得之水文結構，配合鎖管漁業標本戶之漁業活動資料，來探討1998~2001年期間，台灣東北部海域鎖管漁場之漁海況時空間變動特性。由衛星遙測表水溫（或水色）影像與標本戶漁業活動位置之合成圖顯示，台灣東北部海域之鎖管漁場，主要是分布在冷暖水交會之潮境鋒面處，以及湧昇冷水渦邊緣處，而進一步以邊緣偵測分析的結果顯示，台灣東北部海域之潮境鋒面，約離中國大陸沿岸92-259km，而湧昇冷水渦之面積，則約在643-2920平方公里之間變動，且鎖管漁業標本戶之月別平均CPUE，則與潮境鋒面離岸的遠近，以及冷水渦面積的大小成正比關係。此外，由地理資訊系統整合分析之結果發現，在春末夏初時分，台灣東北部海域之鎖管漁場，約是在大陸沿岸水與黑潮水交會的潮境鋒面處形成；而隨時序及潮境鋒面之推移，鎖管漁場之位置於夏季時，則逐漸朝冷水渦週邊海域推移，而此－冷水渦之大小及位置，則會受颱風之影響，而有不同之分布結構，進而影響鎖管漁場之分布型態；秋季時，鎖管漁場則主要是分布在冷水渦週邊海域，且此時為鎖管漁訊之末期，因此CPUE均在較低之水準。綜上可知，台灣東北部海域之鎖管漁場，不但會受海況結構之時空間變動，而有不同的時空分布型態，進而使其有不同之漁獲水準，且台灣東北部海域也會受到異常海氣之影響(如颱風)，而產生異常之海況結構。We studied the squid fishing ground and satellite imageries of the northeastern waters of Taiwan, southern East China Sea, during the period of 1998-2001. Two obvious oceanic features, offshore thermal front and upwelling eddy that varied seasonally, were examined by using image edge detection function. The nearest distance of offshore thermal (or chlorophyll) front away from the coastline of Mainland China and the upwelling size (standard deviation) were generally within the range of 92 to 259 km and 643 to 2920 km^2, respectively. The monthly CPUEs and the spatial fishing position of torch-lighted squid fishery by season were varied with time. The CPUE was positively related with both the nearest distance of offshore thermal front to Mainland China and the size of upwelling eddy. In spring and summer, the fishing grounds were simultaneously formed in the shelf and coastal waters in the southern East China Sea. Its position was also anomaly varied and moved northward to the periphery of the upwelling during summer, as the upwelling was enhanced by passing typhoons. In autumn, the fishing ground was significantly formed further south in the vicinity of upwelling. Our result showed that location of the squid fishing ground was associated not only with oceanographic conditions of an extended area influenced by the Kuroshio, but also with local and instantaneous oceanographic environments (such as typhoon) in the southern East China Sea.