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色学科网书城■ 品牌书店·知名教辅·正版资源 b.zxxk.com 您身边的互联网+敷辅专家 UNIT6主题训练人与环境、人与动植物 1.阅读理解 A (2023山东潍坊一模)Being taken off the endangered species list doesn't guarantee a carefree future for whales.Recent research estimates that the population of Pacific gray whales off North America's West Coast has dwindled by almost a quarter since 2016.Starting in 2019,alarming numbers of dead gray whales were spotted on beaches and floating offshore throughout their habitat,from Mexico to Alaska.The National Marine Fisheries Service defined it as an"Unusual Mortality Event".UMEs are declared when a "significant die-off" occurs and when information is collected to clarify why it occurs. The Arctic has historically low levels of sea ice in recent years,upending the delicate ecosystem that sustains gray whales.Like other migrators,they don't feed on their winter breeding (grounds or along their migration,and must gain weight during the summer to sustain themselves through the rest of the year.Observers using air photography noted the whales looked skinnier and arrived in Mexico in poor condition,which suggested they were not finding enough food during the summer. This die-off is alarmingly similar to the events of 20 years ago,when another UME resulted in a significant drop in the gray whale population.Although the cause was ultimately undetermined,it's thought that the population reached "carrying capacity"-it grew too large for the environment to support it.Although that idea has been suggested for this die-off as well,it's more likely blamed on the changing conditions of the Arctic. Gray whales,hunted almost to extinction by the mid-20th century,were one of the first to be protected from hunting.The Eastern North Pacific population rebounded without pressure from whaling and was taken off the Endangered Species List;the Western North Pacific population is still listed as endangered.This die-off is a reminder that "delisting"doesn't indicate a population's secure future.New threats arise,climate