Density-Dependent Effect Occurs Regardless of Density

Abstract

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.