In compliance with the Endangered Species Act (ESA), the National Marine Fisheries Service (NMFS) and U.S. Fish and Wildlife Service (USFWS) must designate critical habitat for each species under its jurisdiction listed under the ESA. Critical habitat is defined as “specific areas within the geographical area occupied by the species at the time of listing, if they contain physical or biological features essential to conservations, and those features may require special management considerations for protection” and “specific areas outside the geographical area occupied by the species if the agency determines that the area itself is essential for conservation.”
There is currently no critical habitat designation for the blue whale. This does not violate the ESA as it is not required to identify critical habitat for species listed prior to 1978.