River to river: First evidence of eel movement between distant rivers via the sea

New Perspective of Java Eel Conservation: Case Study in Cilacap Riverine and Coastal Area, Central Java, Indonesia

“…The first one is that the elvers look for another way out to continue the migration, whereas the second is predation by carnivorous organisms, and the third is death. In the first alternative possibility, there is evidence that elvers can migrate between rivers through the ocean, but this fact occurs at the yellow eel stages of Anguilla japonica (Kume et al, 2021). Thus, it is possible that elvers who fail to migrate upstream will still look for another small channel or return to a downstream area that is more suitable.…”

Water temperature and precipitation stimulate small-sized Japanese eels to climb a low-height vertical weir

“…Furthermore, the timing of eel climbing seemed to be influenced by water temperature and precipitation. Previously, we had observed a high eel density (0.67–1.05 eels/m 2 ; TL: 93–641 mm) in the upper reaches of a weir in the Akugawa River [ 25 ]. Together, our previous and present findings suggest that eels inhabiting regions upstream of the weir climbed the weir when they were small (60–140 mm TL) and then lived and grew upstream.…”

“…The area from the river mouth to the weir had concrete banks on both sides and was intruded with saline water, whereas the areas upstream of the weir were entirely freshwater areas as the weir prevented the saline water intrusion. Our previous study showed that a high density of eels (0.67–1.05 eels/m 2 ) with various body lengths (93–641 mm TL) is located in the upper reaches of the Akugawa River [ 25 ]. The riverbank of the study area located upstream of the weir mainly consisted of either a masonry revetment on one side and a natural bank on the other side or natural banks on both sides.…”

“…m 2 ) with various body lengths (93-641 mm TL) is located in the upper reaches of the Akugawa River [25]. The riverbank of the study area located upstream of the weir mainly consisted of either a masonry revetment on one side and a natural bank on the other side or natural banks on both sides.…”