Density dependence is likely to act as a regulatory mechanism in fish stocks that are recovering from overfishing. In general, density dependence in fish stocks is assumed to only occur in reproduction and early life stages and is therefore usually modelled as a stock-recruitment relationship. Recent research shows that density dependence can also reduce individual growth in body size later in life. In this study, we show how optimal fishing effort changes with the strength of density dependence in individual growth for four stocks of North Sea flatfish species. Using size-structured population models we show that density dependence arises due to a mechanistic link between the resource availability and life history processes at the individual level. We furthermore show that the stock response to harvesting is either driven by changes in individual reproduction when density dependence in individual growth is weak or by changes in individual growth rate when individual growth is strongly affected by density dependence. These two types or regimes are separated by a sudden shift in dynamics. It is therefore of great importance to account for density dependence in growth when managing fish stocks.

中文翻译：

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密度依赖性个体生长对鱼类种群可持续捕捞和管理的影响

密度依赖性可能作为从过度捕捞中恢复的鱼类种群的调节机制。一般而言，假定鱼类种群的密度依赖性仅发生在繁殖和生命早期阶段，因此通常被建模为种群补充关系。最近的研究表明，密度依赖性还会降低个体在以后生命中的体型增长。在这项研究中，我们展示了四种北海比目鱼种群的最佳捕捞努力量如何随着个体生长的密度依赖强度而变化。使用规模结构的人口模型，我们表明密度依赖性的产生是由于个体层面的资源可用性和生活史过程之间的机械联系。我们进一步表明，当个体生长的密度依赖性较弱时，种群对收获的反应是由个体繁殖的变化驱动的，或者当个体生长受到密度依赖性的强烈影响时，由个体增长率的变化驱动的。这两种类型或制度因动态的突然转变而分开。因此，在管理鱼类种群时考虑密度对生长的依赖性非常重要。