A new biological indicator to assess the ecological status of Mediterranean trout type streams

► We model carrying capacity dynamics for 37 brown trout populations during 12 years. ► We test the accuracy of the density-carrying capacity (D/K) ratio to measure population conservation status. ► We assess the response of D/K ratio to a gradient of increasing environmental harshness and degradation. ► D/K ratio is sensitive to spatio-temporal changes in environmental harshness and degradation. ► D/K ratio is sensitive to both general and life stage specific disturbance factors.