Jüssi Mart, Härkönen Tero, Helle Eero, Jüssi Ivar
Estonian Fund for Nature, Tartu, Estonia.
Ambio. 2008 Mar;37(2):80-5. doi: 10.1579/0044-7447(2008)37[80:dicwrt]2.0.co;2.
Baltic grey seals (Halichoerus grypus) alternate between land and ice breeding, depending on ice conditions. We show that the fitness of grey seal females in terms of pup mortality and quality is reduced when breeding on land as compared with ice. The mean preweaning mortality rate on land was 21.1% (range 0% to 31.6%), and correlated with birth density (range 0.5-5.2 pups 100 m(-2)). The mean mortality rate on ice was 1.5%, where the highest density was 0.2 pups 100 m(-2) in particularly dense breeding groups. Mean weights of pups born on ice were significantly greater (48.3 +/- 8.1 kg) at the onset of moult as compared with pups born on land (37.4 +/- 7.8 kg). Because indices of life-time net reproductive rate (pup survival) and pup quality (weaning weight and health) were more auspicious on ice as compared with land, diminishing ice fields will lower the fitness of Baltic grey seal females and substantially increase the risk for quasi-extinction.
波罗的海灰海豹（Halichoerus grypus）根据冰情在陆地和冰面交替繁殖。我们发现，与在冰面上繁殖相比，灰海豹雌性在陆地上繁殖时，幼崽死亡率和质量方面的适应性会降低。陆地上断奶前的平均死亡率为21.1%（范围为0%至31.6%），且与出生密度相关（范围为每100平方米0.5 - 5.2只幼崽）。冰面上的平均死亡率为1.5%，在特别密集的繁殖群体中，最高密度为每100平方米0.2只幼崽。与在陆地上出生的幼崽（37.4 ± 7.8千克）相比，在冰面上出生的幼崽在换毛开始时的平均体重显著更重（48.3 ± 8.1千克）。由于与陆地相比，冰面上的终生净繁殖率（幼崽存活率）和幼崽质量（断奶体重和健康状况）指标更有利，冰原面积的减少将降低波罗的海灰海豹雌性的适应性，并大幅增加近乎灭绝的风险。
