The population of finless porpoise in the Inland Sea of Japan
The population of finless porpoise in the Inland Sea of Japan
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发表时间：
1979
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影响因子：
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通讯作者：
T. Kasuya;K. Kureha
中科院分区：
文献类型：
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作者：
T. Kasuya;K. Kureha
通过11,549公里的内海巡航观察到的1,194头江豚以及一些辅助观测提供了以下信息。江豚每年主要通过东内海的两个山口往返于太平洋海岸。分娩季节开始的4月密度最高(4900只)，初冬最低(1600只)。独居成体、独居小牛和产犊母牛的比率表现出季节性波动，并允许对繁殖的季节性进行分析。妊娠期约为11个月。分娩发生在4月至8月之间，4月至5月可能是分娩的高峰期。大多数在4月和5月出生的奶牛被怀疑在夏季离开内海。在6到15个月的哺乳期后，从12月到6月开始断奶。连续两年怀孕的情况并不常见。两年的繁殖周期似乎是最常见的。初步估计内海个体的年产量约为870头(雌雄)，年毛繁殖率为17.9%。
The observation of 1,194 finless porpoises made through 11,549 km of sighting cruises in the Inland Sea and some ancillary observations provided the following informations. The porpoise migrates annually to and from the Pacific coast mainly through the two passes at the eastern Inland Sea. The highest density (4,900 individuals) is found in April at the beginning of parturition season, and the lowest (1,600) in early winter. The ratios of solitary adults, of solitary calves, and of cows with calf show seasonal fluctuation, and allow the analyses of the seasonality of reproduction. Gestation last for about 11 months. Parturition occurs between April and August with a possible peak in April and May. Most of the cows with calf born in April and May are suspected to leave the Inland Sea in summer months. Weaning occurs from December to June after a nursing period ranging from 6 to 15 months. Pregnancies in two contiguous years are not frequent. A 2-year breeding cycle seems to be most common. Annual production of about 870 calves (both sexes), and gross annual reproductive rate of 17.9% are provisionally estimated for the individuals in the Inland Sea.