Die-Offs of Pre-Spawn Adult Pink Salmon and Chum Salmon in Southeastern Alaska

About 300 pre-spawn adult pink salmon (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) died in August 1981 in the intertidal reach of Porcupine Creek, a small stream in an old-growth forest. A combination of low stream flow and neap tides triggered the die-off, and about 1% of the pink salmon and chum salmon spawners died upon returning to Porcupine Creek in 1981. Anoxia, rather than temperature, caused most of the deaths because the maximum stream temperature was 19 C—well below lethal temperatures. Conditions similar to those in 1981 recur in Porcupine Creek about once every 8 years. This type of die-off also appears to be common in other streams in southeastern Alaska and can be predicted from the number of salmon returning, amount of precipitation, and height of the tide.