A complex past: historical and contemporary fisheries demonstrate nonlinear dynamics and a loss of determinism

ABSTRACT: Nonlinear dynamics have been widely demonstrated in natural systems. In marine fisheries ecosystems, such dynamics have primarily been associated with exploited species, suggesting an anthropogenic stressor may explain their prevalence. However, this earlier work compared co-occurring exploited and unexploited species, as opposed to analyzing the same species before and after significant harvesting pressure. The former does not control for either differences between species or the reality of indirect and long-lasting fishing impacts. Here, nonlinear dynamics were investigated for the same species before and after significant changes in the magnitude of harvesting. We found nonlinear signatures prevalent prior to heavy industrial exploitation, and also found that these dynamics were highly deterministic. This demonstrates that nonlinearity existed in a complex marine system prior to extensive human influence and suggests such behavior may be an innate property of these populations. Results also show a reduction in deterministic dynamics post industrialization, suggesting that fishing can undermine the dynamics and resilience of marine populations and render fisheries model output less predictable for management.