Reproductive biology of the viviparous sea snake Emydocephalus ijimae (Reptilia: Elapidae: Hydrophiinae) under a seasonal environment in the NorthernHemisphere

Reproductive traits of Emydocephalus ijimae were examined on the basis of specimens from shallow waters around the central Ryukyus, Japan. Sampling was carried out from December 1979 until November 1980 (with the exception of September), and yielded a total of 240 specimens. Gonadal examinations revealed that males and females mature at 550-600 mm and 500 - 550 mm snout-vent length (SVL), respectively. We therefore regarded female snakes > 550 mm SVL and male snakes >500 mm SVL as adults. Mean length of the largest ovarian follicles in the monthly adult female sample increased gradually from July to March, and rapidly from March to April, and then swiftly decreased from April to June. Oviducal eggs occurred only in samples from May to November, although the occurrence of one gravid female in early January was recently reported. Possible neonates (i.e. juveniles as large as the largest embryos [280-320 mm in SVL]) were found from November to January. These data suggest that ovulation occurs from May to June and parturition from November to January after 6-8 months of gestation. Of 19 adult females collected in June, ten (52.6%) were gravid, whereas the remainder had neither oviducal eggs nor enlarged ovarian follicles close to ovulation. Likewise, both gravid and non-gravid females were observed in each of the July-November samples, although their sample sizes were much smaller (4-8) and frequencies of gravid individuals varied considerably (0-50%). It is likely that the overall frequency of reproduction in individual females is biennial or even less frequent. Clutch size varied from 1 to 4 eggs, and showed no significant correlation with maternal body size (as represented by SVL or BW). In adult males, on the other hand, gonadal index (total mass of gonads × 100/body mass) increased from May to November, and largely decreased from November to April. Present results indicate that the reproductive activities of both male and female E. ijimae are synchronized and seasonal, as in some other lower latitude marine snakes.