Variations from 1910 to circa 1985.
See also: https://swfsc.noaa.gov/publications/CR/1989/8937.PDF
and many other papers.
The routine and fairly regular (several decades from peak to peak) variation in
sardine populations of the Californian current may be explained by plankton populations.
These variations are well studies, with studies and data commencing in the early part of the
To label the current decline in sardine numbers proof of a man made effect of any kind,
including ascribing the Fukushima nuclear disaster as a cause is not scientific.
Any explanation must be also able to explain the rapid declines in the period after 1910, the period after World War 2 and so on. Likewise any rational explanation must explain the high peaks which occurred between the low periods.
While anything is possible, rationality demands a consistent and predictable solution.