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国内血統登録書から見たゴマフアザラシの
飼育下繁殖の年齢と回数
寺沢 文男
新江ノ島水族館
（日本動物園水族館協会種保存委員会ゴマフアザラシ種別調整者）

要約
1）血統登録台帳（1986年～2008年）の記録から，飼育下ゴマフアザラシの繁殖年齢と繁殖数を分析した．調査個体の類別では，「繁殖個体」が540頭（52.0％），「保護個体」が473頭（45.5％），「不明個体」が26頭（2.5％）であった．
2）「繁殖個体」540頭中，登録前および繁殖年「不明個体」を除くと，母獣の確定数は450頭，父獣265頭であった．
3）最多繁殖関与数は，母獣12回，父獣17回であった．
4）出産時の母獣の最小年齢は，「繁殖個体」で2歳9ヵ月，最高年齢は「保護個体」で32歳であった．最多出生年齢は8歳であった．
5）出産時の父獣最小年齢は，「保護個体」で3歳以上，最高年齢は「保護個体」で30歳であった．父獣でも最多出生年齢は8歳であった．
6) 「繁殖」および「保護」由来の母獣，父獣で4～10歳，11～17歳の繁殖総頭数は，それぞれの80％以上を占めた．
7）出産回毎の新生子生存率は，1回目62.5％（生存90頭:死亡54頭），2回目73.4％（69:25），3回目78.1％（57:16）と増加した．
8) 連続繁殖数は6年間で6頭が最多記録であり，4年間で5頭（双子1組）の記録もあった．



Ages and numbers of Captive Breeding for Spotted Seal Viewed from Internal Studbook
Fumio Terasawa
Enoshima Aquarium
(Coordinator of Spotted Seal Studbook, JAZA)

ABSTRACT
The current status of captive breeding for Spotted Seals was surveyed through the Japanese Association of Zoos and Aquariums (JAZA) Studbooks from 1986 to 2008. This study was analyzed based on 540 animals born in captivity (ABCs).
In 540 ABCs, cases for known mother were 450 and for known father were 265 excluding animals with uncertain birth years and those born before these studbooks were surveyed.
In 450 mothers of ABCs, 147 were ABCs, 279 seals were animals rescued from the wild (ARWs), and 24 were origin obscurities. In 265 fathers of ABCs, 120 were ABCs, 116 were ARWs, and 29 were origin obscurities.
In females, the youngest birth age for ARWs was estimated to be more than 2 years-old, and for ABCs was 2 years and 9 months. The oldest birth age for ARWs was estimated to be 32 years-old, and for ABCs, 25 years-old. The most births according to age were 8 years-old in both ABCs and ARWs.
In males, the youngest birth age for ARWs sired the previous year was estimated to be more than 3 years-old, and the oldest birth age for ARWs was estimated to be 30 years-old, and for ABCs, 23 years-old. The most births according to age were also 8 years-old for both ABCs and ARWs.
In females and males, the numbers of first-time births increased from 4 to 5 years-old. Therefore, it is suggested that females and males reach sexual maturity from 3 to 4 years-old.
The highest number of births for one female and one male during a lifespan was 12 and 17 respectively. In the same female, 6 consecutive years with 6 births was the longest and most on the record, and all pups were alive at birth. Furthermore, there was one pair of twins in 540 ABCs, and both of the pups were males. One infant died at 24 days after birth, and another survived more than 14 years.
In females and males of ABCs and ARWs, more than 80％ of all births were between the ages of 4-10 years-old and 11-17 years-old.
The survival rates for pups from the first birth to third were 62.5％ (90 survivals; 54 deaths), 73.4％ and 78.1％, respectively.