but also a problem for the mother. 但对母熊而言却是一个问题

40. and has lost half her body weight.
    失去了一半的体重
41. Now she converts the last of her fat reserves into milk for her cubs.
    现在它将仅剩的一点脂肪 变成乳汁喂养它的宝贝们
42. The spring sun brings warmth
    春天的太阳带来了温暖
43. but also a problem for the mother.
    但对母熊而言却是一个问题
44. It starts to melt the sea ice.
    海面的冰层开始融化
45. That is where she hunts for the seal she needs to feed her cubs.
    而母熊则需要在那里捕杀海豹 喂养幼熊
46. And she must get there before the ice breaks up.
    因此它必须在冰层破碎之前到达那里

来自《行星地球 第一季 第一集 Planet Earth S01E01 从北极到南极》第 43 行