claim: Stress from unusually warm ocean water heated by man-made climate change and the natural El Niño climate pattern caused the die-off.
evidence: 1945/1946: The PDO changed to a "cool" phase, the pattern of this regime shift is similar to the 1970s episode with maximum amplitude in the subarctic and subtropical front but with a greater signature near the Japan while the 1970s shift was stronger near the American west coast.