摘要
根据冰的条件,波罗的海灰海豹(Halichoerus grypus)在陆地和冰面上交替繁殖。我们指出,与冰面相比,灰海豹雌兽在陆地上繁殖的状况以幼仔死亡率和质量衡量均有下降。陆地上断奶前的平均死亡率是21.1%(范围0%～31.6%),与出生密度相关(范围0.5～5.2头幼仔/100m^2)。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0.2头幼仔/100m^2。在开始换毛时,冰上出生的幼仔平均体重(48.3±8.1kg)明显高于陆地出生的幼仔(37.4±7.8kg)。与陆地相比,冰上终生净繁殖率(幼仔存活)和幼仔质量(断奶体重和健康)的指标更为有利,所以冰面逐渐缩小,会降低波罗的海灰海豹雌兽的健康,并显著增加准灭绝的危险性。
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 nsk for quasi-extinction.
