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).