It found that immigration reversed what would have been major population decreases in 18 cities.

调查发现，移民扭转了18个城市的主要人口减少的趋势。

In St. Louis and other places, immigrants are helping halt population decreases in urban areas.

在圣路易斯和其他地方，移民正有助于阻止城市地区的人口减少。

This week, the North Atlantic Right Whale Consortium (NARWC) said the population decrease appears to have leveled off.

本周，北大西洋露脊鲸联盟(NARWC)表示，种群数量的减少似乎已经趋于平稳。

He argues that because the whale population decreased, the orcas in the area had to eat otters instead of whales.

他认为因为鲸鱼数量减少，该地区的虎鲸不得不吃水獭。

This may play a role in a projected 30 percent population decrease by 2050. Life on top of the world comes with many challenges.

预计到2050年，北极熊数量会减少三成。它们在世界之巅的生活会引来许多挑战。

They population decreased quickly because of much sickness.

人中因疾病减少得很快。

So bottom-feeding fish populations may increase, even if plankton-eating fish population decrease.

因此，即使以浮游生物为食的鱼类数量减少，底栖鱼类数量也可能会增加。