In response to a petition to list under the U.S. Endangered Species Act both spring-run and fall-run Chinook salmon in the Upper Klamath and Trinity Rivers (UKTR) Chinook Salmon Evolutionarily Significant Unit (ESU) the National Marine Fisheries Service (NMFS) Southwest Fisheries Science Center convened a Biological Review Team (BRT) to evaluate new information they determined to be most relevant to the questions of ESU
configuration and status. This included information provided by the Petitioners in their petition, information deemed pertinent by the BRT, and information provided to the NMFS Southwest Regional Office by other parties interested in this issue. The purpose of this Technical Memorandum is to document the BRT’s review and analysis of this information and to report their findings. Most importantly, the BRT concluded that the new information supported the existing UKTR Chinook ESU configuration with springrun and fall-run populations included in a single ESU, and that the ESU is currently at a low risk of extinction within the next 100 years.