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

• Published in: Ecological indicators Vol. 20; pp. 295 - 303
• Main Authors: Ayllón, Daniel, Almodóvar, Ana, Nicola, Graciela G., Parra, Irene, Elvira, Benigno
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2012
• Subjects: age structure; Anthropogenic stressors; Bioindicators; carrying capacity; climatic factors; conservation status; Degradation; Ecological status; Ecology; Environmental degradation; Fish; freshwater ecosystems; Habitat modelling; humans; Indicators; Mathematical models; regression analysis; Rivers; Salmo trutta; species diversity; Streams; Trout; MED; Bioindicators; Habitat modelling; Anthropogenic stressors; Environmental degradation; Ecological status
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2012.02.028

► 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. Fuelled by the generalized degradation of freshwater ecosystems, the development of tools to assess their ecological status has been the focus of intensive research in the last decades. Although fish are one of the key biological quality elements used to describe the ecological status of rivers, fish metrics that accurately respond to disturbances in Mediterranean trout type streams are still lacking. In these systems, multimetric indices are not optimal indicators because of their low species richness and abundances, thus alternative approaches are needed. Since carrying capacity defines the potential maximum abundance of fish that can be sustained by a river, its relationship with actual density (D/K ratio) could be an accurate indicator of population conservation status and consequently of the ecological status of the river. Based on this rationale, we modeled carrying capacity dynamics for 37 brown trout populations during a 12-year study period. We analyzed the response of the D/K ratio to a gradient of increasing environmental harshness and degradation in order to assess its suitability to accurately measure brown trout conservation status. Our results showed that the D/K ratio was highly sensitive to temporal and spatial variations in environmental conditions and the levels of human-induced environmental degradation. Variations in the environmental and human degradation factors included in the best explaining regression models developed for the whole population and by age classes accounted for between 58 and 81% of the variation in the D/K ratio. Likewise, the D/K ratio was sensitive to both general and life stage specific disturbance factors. Further analyses helped identify the factors limiting population abundance. Therefore, the D/K ratio could be an interesting indicator to consider when defining objective management plans and corrective actions in degraded rivers and streams subject to Mediterranean climatic conditions.