Maximum sustainable yield (MSY) is the most
important concept in fisheries resource management. MSY can be established
based on the concept of the density-dependent effect. However, the concept that a density-dependent effect controls
the fluctuation of the population living in the ocean is controversial. This
paper discusses the validity of the density-dependent effect focusing on the
stock-recruitment relationship (SRR). In many cases, the SRR shows a clockwise
or ant-clockwise loop. If we try to explain the population fluctuations using
the density-dependent effect, the clockwise or anti-clockwise loop observed in
SRR cannot be explained. However, the mechanism proposed here can well
reproduce the phenomena observed in many SRR including the clockwise or
anti-clockwise loop. In other words, the most important relationship between
stock and recruitment is likely to be the interspecific relationship and/or environmental
conditions, not the density-dependent effect. If the density-dependent effect
observed in SRR is not real, then the MSY theory is not valid, and all the
management procedures based on MSY would also not be valid.
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