Defining a “population ” under the Endangered Species Act∗

The original form of this article was submitted on March 31, 1995 as the Di-rect Service Industries ’ comments to draft regulations proposed by the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS, now NOAA Fisheries). The two agencies wanted to define “distinct population segments ” under the Endangered Species Act (ESA) so that they would have a consistent definition for their regulatory decisions. Unfortunately, administrative convenience and political accommodation replaced science in the definition. The two agencies also gave different names to the same contrived groupings. The U.S. Fish and Wildlife Service considers a “discrete vertebrate population segment ” to be a species under the ESA while the National Marine Fisheries Service calls the equivalent group an “evolutionarily significant unit”. The draft regulations were adopted as permanent and have been in place ever since