When does a species go extinct?

According to a recent article "Facing Extinction: California Fishes" by UC Davis researchers Peter Moyle and Jason Baumsteiger, this isn't an easy question.

"At least two species of California fishes appear to be facing imminent extinction in the wild: delta smelt and winter-run Chinook salmon. 



These species could join about 57 other North American fishes declared extinct. If we are fortunate, these species will continue to scrape by with small populations, maintained through considerable human effort.  But if we are unfortunate, these fishes, and likely other species, will disappear in the near future.   This likelihood suggests we need answers to the following questions:

  1. How do we know when a species is extinct? How long do we have to wait from the time the apparent last individual is captured to declaration of extinction?
  2. Who makes the official determination that a species is extinct?
  3. What role do captive populations play in the extinction process?
  4. Why is there a need to have an extinction policy in place?"

Read more at the California WaterBlog: