query: When did the pallid sturgeon become an endangered species?
passage: Pallid sturgeon
In 1990, the U.S. Fish and Wildlife Service placed the pallid sturgeon on its endangered species list because few young individuals had been observed in the preceding decade and sightings had greatly diminished;[5] the species is now rarely seen in the wild. It was the first fish species in the Missouri River drainage area to be listed as endangered, and a loss of its habitat is thought to be responsible for its decline. The vast majority of the Missouri River drainage system has been channeled and dammed, reducing the gravel deposits and slow-moving side channels that are its favored spawning areas. Until the middle of the 20th century, pallid sturgeon were common and anglers found catching such a large fish in fresh water a rewarding experience. The species is considered to be good-tasting, and its eggs have been used as caviar, although less commonly than those of many other sturgeon.[6]
passage: Polites mardon
The Mardon skipper butterfly is currently listed as an endangered species in Washington state and classified as a federal endangered species. Its status denotes a high priority for conservation efforts. Over the years, studies have been assessing the decline of this species in the Puget prairies, by conducting population counts and habitat characteristics and their effect on the Mardon skipper's life cycle.