Site description
The Yukon River watershed is massive, draining approximately 850,000 km2 and flowing more than 3,000 km from its source in Canada to the Bering Sea of Alaska. Made famous in the writings of resident Syndey Huntington (Huntington 1993), the Koyukuk River drains 83,000 km2‑and flows ca. 725 km before its confluence with the Yukon River where water flows another ca. 775 km to the ocean. Summer Chum Salmon of the Koyukuk are primarily destined to spawning grounds on the Gisasa River and Henshaw Creek (Janzen and Stern 1998), where weirs allow the quantification of spawner numbers and documentation of age, sex, and length of returning adults. Examination of size selective en route mortality (see below) was done only using data from Henshaw Creek as our survey was done upstream of the Gisasa River confluence with the Koyukuk. The Koyukuk River is a major producer of summer chum salmon; extensive telemetry tracking of 2,431 migrating salmon in 2014 and 2015 revealed approximately one out of every four fish return to the Koyukuk and its tributaries (Larsen et al. 2017).