Elephant seal female breeding histories at Año Nuevo

The elephant seal (Mirounga angustirostris) breeding colony at Año Nuevo, California, was founded in 1961, and since monitored closely until the present. Since 1968 a research group at the University of California, Santa Cruz, has studied it in detail. Individually identified females were monitored during the breeding season, and pupping records of many throughout their lifetimes were assembled. We address here the maximum reproductive success of females using the lifetime breeding histories. Females lived to a maximum of 23 years and were observed breeding in as many as 17 seasons. One female was observed with a pup nearby in 16 consecutive seasons, from age 4 through age 19. We compared females that gave birth to 10 or more pups (Supermoms) with females that bred at least once but produced fewer than 10 pups (Generic moms). Less than 17% of female weanlings bred at least once. Only 0.87% of females in the sample became Supermoms. We conclude that exceptional reproductive success in elephant seals is associated with giving birth annually, living long and weaning pups successfully. Once female elephant seals begin reproducing they are pregnant or nursing throughout life until they die.

位于美国加利福尼亚州阿尼奥纽埃罗的北象海豹（Mirounga angustirostris）繁殖种群始建于1961年，自此之后一直受到密切监测直至今日。自1968年起，加州大学圣克鲁兹分校的一支研究团队对该种群开展了详尽研究。研究人员在繁殖季对经个体标识的雌性海豹进行监测，并收集了众多雌性个体终生的产仔记录。本研究基于雌性海豹的终生繁殖历史，探讨其最高繁殖成功率。雌性海豹的最长寿命可达23年，观测到的繁殖季最多可达17个。有一头雌性海豹在4岁至19岁期间，连续16个繁殖季均在其领地附近产仔。本研究将产仔10头及以上的雌性海豹（Supermoms，超级母亲）与至少繁殖过一次但产仔不足10头的雌性海豹（Generic moms，普通母亲）进行了对比分析。仅有不到17%的雌性断奶幼崽能够至少成功繁殖一次。样本中仅有0.87%的雌性个体成为超级母亲（Supermoms）。研究结论表明，北象海豹的超高繁殖成功率与其每年产仔、寿命更长且成功抚育幼崽密切相关。雌性北象海豹一旦开始繁殖，便会在余生中始终处于怀孕或哺乳状态，直至死亡。