Inshore Migration of The Tropical Eels Anguilla Spp. Recruiting to The Poigar River Estuary on North Sulawesi Island

To understand ecological and behavioral aspects of inshore migration of tropical eels, Anguilla spp., we collected 32 836 glass eels in the Poigar River estuary on north Sulawesi Island, Indonesia, in monthly collections from 1997 to 1999. The specimens were identified using morphological characters, and 3 species, A. celebesensis, A. marmorata, and A. bicolor pacifica, were found each year in fluctuating abundances. A. celebesensis was the most abundant species and comprised 73.5, 79.5, and 81.9% of all glass eels recruiting to the estuary of the Poigar River in 1997, 1998, and 1999, respectively. This species was relatively abundant in all 3 years with peaks during June in 1997 and 1998, and during September in 1999. A. marmorata was the second most abundant species and comprised 23.8, 18.8, and 17.7% of the yearly catches, respectively, and reached peaks in abundance during June in 1997 and 1998, and during January in 1999. A. bicolor pacifica comprised only 2.7, 1.7, and 0.3% of the yearly catches, respectively, with peak catches in June in 1997, in January in 1998, and in January and February in 1999. A. celebesensis and A. marmorata were collected almost throughout the year in 1997, 1998, and 1999, suggesting that in contrast to the temperate eels that recruit during half the year from winter to spring, these tropical eel species recruit to some degree throughout the year. Glass eels clearly were more abundant during new moon sampling events, with a total of 3075, 183, 3, and 90 glass eels collected in 10 sampling periods during new moon, waxing moon, full moon, and waning moon, respectively. All glass eels were collected at night (18:00 to 05:00 h) when light intensity ranged from 0 to 1.86 lux, and no glass eels were collected during the day (06:00 to 17:00 h) when light intensity ranged from 500 to 150 000 lux. During new moon, more glass eels were collected during flood tide than during ebb tide. These results suggest that a greater number of glass eels recruited to the Poigar River estuary at night, during new moon and during flood tide. Marine Ecology Progress Series, Vol. 221. Hal. 233-243