Salmon dying off in Prince of Wales drainages amid low, warm water

Salmon are dying off in several Prince of Wales Island drainages, most notably the Thorne River and Staney Creek, where low, warm water has killed fish and is concentrating survivors in pools and deeper runs. ADF&G area management biologist Craig Schwanke reported the die-offs in the department's Aug. 20 sport fishing report, which gives no mortality estimate or temperature, flow and dissolved-oxygen readings.

Rivers and creeks across the island remain very low for lack of rain, and pink salmon entering fresh water are stacking up as a result. Sockeye have already started spawning in some systems, including the Thorne, Sarkar and Karta rivers and Hatchery, Ratz and Eagle creeks.

Die-offs here are not new. ADF&G Technical Paper 308, a 2011 study of subsistence sockeye harvest in Klawock Inlet, records that large die-offs occur periodically in island streams during "dry hot weather, low water levels and large salmon runs," including events in 1993 and 1999. Klawock subsistence harvesters have asked the Board of Fisheries to further limit harvest in the estuary over concerns about the sockeye run's strength. Alaska News has previously covered a separate strain this season: kings, coho and pink salmon all running below average.

Research describes how such die-offs happen, though without site-specific measurements here. A USDA Climate Hubs presentation by research fisheries scientist Ryan Bellmore says drought-driven changes in stream flow and temperature affect all freshwater salmon life stages, limiting river access and reducing spawning area. The Alaska Climate Research Center writes that low water, high temperature and high fish density together drive dissolved oxygen into a range it calls "potentially ecosystem-altering." Warming rivers and summer drought pose the same risk to salmon across Alaska.

The same drainages carry the island's resident fisheries. Schwanke's report lists the Thorne River and Ratz Creek among productive waters for rainbow trout, cutthroat trout and Dolly Varden.