可悲的是，人类活动是帝王蝶数量减少的主要原因。

Sadly, human activity is the main reason why the number of monarch butterflies is falling.

濒危物种的数量减少了很多。

The population of the endangered species has diminished drastically.

红细胞数量减少可能导致贫血。

A decrease in erythrocyte count can lead to anemia.

血小板的数量减少可能导致出血问题。

A decrease in platelet count can lead to bleeding problems.

由于数量减少，独角鲸是一种受保护的物种。

The narwhal is a protected species due to its declining population.

岛屿周围的水域被过度捕捞，导致鱼类数量减少。

The waters around the island are overfished, leading to a decline in fish populations.

家庭佣工的数量减少了。

Fewer home helpers are available.

因此，他们促使了北极熊和海豹的数量减少。

So they have pushed down the number of polar bears.

这年,小龙虾的数量减少了.

This year the numbers of small lobsters are dropping.

后来雕像的数量减少了一半。

Later the amount was cut in half.