Life history traits of the giant mottled eel Anguilla marmorata in the northwestern Pacific as revealed from otolith daily growth increment and microchemistry

• Main Authors: Nico Jose Leander, 林德
• Other Authors: Wann-Nian Tzeng
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/09383143028330577353

博士 === 國立臺灣大學 === 漁業科學研究所 === 102 === The present study investigated the recruitment dynamics and early life history of the tropical eel Anguilla marmorata in the northwestern Pacific as well as the migratory environmental history of the eel in the Philippine waters. Analysis of the species composition of the recruiting glass eels in the estuary of the Hsiukuluan River, Eastern Taiwan from 2005-2009 revealed that A. marmorata was the most dominant eel species making up to 98.4% of the total catch while there were very few A. bicolor pacifica (1.6%) and A. japonica (<1%). Tropical eel species A. marmorata recruited mainly to the estuary during spring to summer but can be found year-round while A. bicolor pacifica recruited mainly during autumn. The temperate species, A. japonica, recruited mainly during winter. Examinations of the otolith daily growth increments of A. marmorata and A. japonica glass eels collected from various rivers and estuaries in East Asia from 1992-2008 indicated that age at metamorphosis and early growth rate seem to play an important role in the segregative migration and latitudinal distribution of these two sympatric eel species in the northwestern Pacific. Faster-growing and earlier-metamorphosing leptocephali of A. marmorata recruited earlier in the Philippines while its slower-growing, delayed metamorphosing leptocephali dispersed southward (via the Mindanao Current) and northward (via the Kuroshio Current). On the other hand, the A. japonica leptocephali which arrive in the Philippine waters are apparently too young to metamorphose and migrate towards the estuaries so it will continue to drift northwards. This must be the reason why Japanese eels are seldom found in the Philippines while A. marmorata occurs in abundance. The Sr:Ca profile in the otoliths of yellow-stage A. marmorata collected in the river of eastern Luzon, the Philippines in August 2008 revealed that it’s migratory environmental history is quite different from that previously reported from Japan and Vietnam and from A. japonica. Electron probe microanalyzer showed that after the elver check, the Sr:Ca ratio until the otolith edge were less than 4 x 10-3, indicating that after recruitment, A. marmorata just stayed in freshwater until capture, which is similar to that of A. marmorata in Taiwan. On the contrary, A. japonica has a more flexible migratory behavior in the yellow stage. It can migrate among seawater, brackish water and freshwater in the yellow eel stage. Interspecific competition, environmental factors and the productivity of the environment may play an important role in the habitat preference of A. marmorata throughout its species range. The findings of this study can provide the information for the eel conservation and management.