Rhythmic activity of inshore migration of tropical freshwater glass eels of the genus Anguilla
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Rhythmic activity of inshore migration of tropical freshwater glass eels of the genus Anguilla Takaomi Arai & Hagi Yulia Sugeha & Daniel Limbong & Katsumi Tsukamoto
Received: 22 March 2020 / Accepted: 6 September 2020 # Springer Nature B.V. 2020
Abstract Compared with temperate Anguilla, little is known about the early marine migration and recruitment mechanisms of these tropical eels. To understand the ecological and behavioural mechanisms of their inshore migration in tropical Anguilla, systematic research on their periodicity of inshore migration was conducted for 24 h over 9 to 13 consecutive days before and after the new moon dates four times in one year. Glass eel (juvenile) collections (151 to 4371 specimens during each survey period) in the Poigar River, north Sulawesi Island, Indonesia indicated a lunar periodicity, in which peak recruitment continued for 2 to 4 days during the new moon period; then, the recruitment sharply decreased before and after the new moon. Daily glass eel migration occurred in two peaks during the ebb (20:00) and flood (02:00) tides, while there was no significant
Daniel Limbong was Deceased T. Arai (*) Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, BE 1410, Brunei Darussalam e-mail: [email protected] H. Y. Sugeha Research Centre for Oceanography, Indonesian Institute of Sciences, Ancol Timur, Jakarta 14430, Indonesia D. Limbong Sintuwu Maroso University, Poso 94619, Indonesia K. Tsukamoto Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1, Yayoi, Bukyo, Tokyo 113-8657, Japan
different glass eel recruitment between the flood tide and ebb tides. Although the “selective tidal stream transport” that glass eels utilize during the flood tide for recruitment is widely accepted to be the main mechanism of inshore migration behaviour through estuaries to freshwater habitats for temperate glass eels, we did not find this mechanism during this study. These results suggest that the main recruitment mechanism for tropical glass eels may be associated with both endogenous rhythms (biological clock) and exogenous factors (tidal orientation) in the study site. The rhythmic activity of migrating tropical glass eels found in this study also contributes not only to understanding the biological and ecological implications but also provides clues for stock management and conservation of Anguilla, which have been critically declining in recruitment worldwide in recent decades. Keywords Anguilla . Glass eel . Recruitment . Inshore migration . Upstream migration . Migratory behavior
Introduction Due to their mysterious life history and economic importance, freshwater eels of the genus Anguilla have been the focus of considerable scientific research for decades. However, despite these efforts, most of the aspects of their early life history and recruitment mechanisms are still not completely understood. The genus Anguilla is currently recognized as including 16 species, three of which are fur
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