To accumulate information on the larval transportation of the freshwater eels in the North Pacific, we examined the ages of the giant mottled eel Anguilla marmorata recruited at the northern Philippines. The glass eel specimens analyzed were collected at the river mouth of the Cagayan River in the Luzon Island in January 2009, November 2011 and November 2012, and the daily increment rings of the otoliths were observed to determine the ages at recruitment (n=14). There was no significant difference in the ages at recruitment among the 2009(147.0 ± 24.4 days; 126–182), 2011(145.2 ± 17.3; 122–161) and 2012-groups (136.0 ± 11.1; 122–145), and were in the range of those in the previous studies at the same place. Further efforts to accumulate information on the ages at recruitment at various localities and timings will be important to comprehensively understand the early life history of A. marmorata in the North Pacific.
When animals move across the water surface, they push out surrounding water, creating waves. This work of wave formation is considered the largest drag component at the water surface and is known as wave drag. In order to avoid wave drag, most marine mammals travel submerged over longer distances and minimize the time spent swimming at the surface. We attached an accelerometer to a trained bottlenose dolphin and evaluated the effect of wave drag from the dolphin's swimming speed and stroking efforts such as stroke frequency and body amplitude. We found that the body amplitude was significantly larger at the surface than at a depth of 3 m within a given speed range; however, the difference was not clear enough to quanti- tatively evaluate the effect of wave drag. The reasons might be due to the limited size of the pool used in this study. Thus a more controlled experiment with longer swimming distance, a deeper pool, and better control of the dolphin's swimming speed is required to further our understanding of the effect of wave drag on dolphins.
