First capture of post-spawning female of the Japanese eel Anguilla japonica at the southern West Mariana Ridge

Abstract

Two adult male freshwater eels, Anguilla japonica, were captured in June 2008 in the West Mariana Ridge (13°N, 142°E) in the North Pacific, but collections of females have yet to be reported. In September 2008, we successfully caught two adult female A. japonica, 55.5 and 66.2 cm in total length, in the adjacent but northern area (14°N, 143°E). Six newly hatched eel larvae (pre-leptocephali) were also collected by subsequent plankton sampling conducted near the female catch area. Female adults appeared to be in the post-spawning state, probably a considerable time after spawning, since a small number of remarkably regressed oocytes (50-250 lm in diameter) were observed in the ovaries. Capture of post-spawning female eels and newly hatched larvae near the Suruga Seamount (14°N) together with the previous collection of mature males in the southern area (13°N) corroborates that the area along the West Mariana Ridge is the spawning area of this species, but suggests that the eel spawning may occur over a wider area than previously expected.

Discovery of a spawning area of the common Japanese conger Conger myriaster along the Kyushu-Palau Ridge in the western North Pacific

“…Research cruise and collection of C. myriaster larvae The C. myriaster collections were made as a part of the expedition to study the spawning ecology of the Japanese eel that was conducted by the R/V Kaiyo Maru of the Fisheries Agency of Japan (KY-08-4, 20 August to 15 September 2008) [24] along a 12°N, 135.5°E to 13°N, 136°E line and a 136°E line between 13°N and 22°N that roughly followed the Kyushu-Palau Ridge in the North Pacific ( Fig. 1) from 5 to 8 September 2008.…”

“…This suggests that C. myriaster had spawned in September and probably also in June quite near to or just to the east of the Kyushu-Palau Ridge. This oceanic ridge could play an important role as a landmark for the spawning area, as appears to be the case for the Japanese eel that spawns just to the west of the West Mariana Ridge [22][23][24][25]. Since the oceanic ridge crest within the present survey area (13-22°N) is quite deep (approximately 2,500-3,500 m deep), except for Okinotorishima Island, C. myriaster spawning appears to occur in a pelagic environment similar to that of the Japanese eel, which has been studied through the collection of mature adults [23][24][25], naturally spawned eggs, and newly hatched preleptocephali [25] along the West Mariana Ridge.…”

“…This oceanic ridge could play an important role as a landmark for the spawning area, as appears to be the case for the Japanese eel that spawns just to the west of the West Mariana Ridge [22][23][24][25]. Since the oceanic ridge crest within the present survey area (13-22°N) is quite deep (approximately 2,500-3,500 m deep), except for Okinotorishima Island, C. myriaster spawning appears to occur in a pelagic environment similar to that of the Japanese eel, which has been studied through the collection of mature adults [23][24][25], naturally spawned eggs, and newly hatched preleptocephali [25] along the West Mariana Ridge. The Kyushu-Palau Ridge is at the boundary between the Philippine Basin (5,000-6,000 m deep) and the West Mariana Basin (approximately 4,000-5,000 m deep), and may provide longitudinal cues for C. myriaster adults to aggregate and spawn due to possible geomagnetic anomalies if they have a magnetic sense like anguillid eels [25,32].…”

“…Since the spawning area of the Japanese eel was found to occur along the West Mariana Ridge within the latitudes of the main part of the NEC (12-14°N) [22][23][24][25], with their larvae being transported westward by the NEC and then transferring to the Kuroshio to recruit to East Asia [39,[44][45][46], it appears that C. myriaster has a slightly different spawning and recruitment strategy. It has also been estimated that C. myriaster larvae are transported westerly Fig.…”

“…This was considered to be in an analogous location to the offshore spawning area of the American conger eel, C. oceanicus, in the western North Atlantic [20,21]. The offshore distribution of these larvae showed that C. myriaster spawned in an offshore area far south of its growth habitats in East Asia, and that its adults and larvae perform long-distance migrations similar to catadromous eel species such as the Japanese eel Anguilla japonica, which has been found to spawn in a narrow area along the West Mariana Ridge [22][23][24][25]. However, further confirmation beyond those larvae caught at one station is needed to help determine the location of the spawning area of C. myriaster and identify the possible landmarks used to find the spawning area.…”