Modelling of thermal habitat loss of brown trout (Salmo trutta) due to the impact of climate warming

Abstract

Fish habitats and river ecosystems are threatened by climate warming, with some endangered species such as the brown trout being particularly vulnerable. Heat exchange models, such as the SSTEMP, are useful tools for analyzing the thermal habitat of rivers with marginal field measurements. The brown trout is a native and valuable fish species in the southern Caspian Sea basin, and the Absefid, Delichai and Elarm streams are main habitats for the brown trout in the Lar National Park. The aim of the present study was to develop a simple and inexpensive method to estimate the effect of climate warming on thermal habitats in recent years in the Lar National Park and to use the results to improve environmental management in the park. Our results indicate that the habitats in the downstream reach of the Absefid stream is in a critical condition, with existing environmental stresses being identified for four years of the five-year simulation period. The stretches of the Delichai are not in a critical condition, although in some years, the environmental stress was as high as 40% downstream; therefore, the habitat is likely to be unsuitable only at the downstream section. The Elarm stream has the lowest thermal stress along its length. The dissolved oxygen level is sufficient in all of the habitats, and it is not significantly altered by any increase in temperature observed downstream. In general, about 8 km of the total 25 km lengths of the studied riverine habitats are of great concern, and the loss of the Absefid as a habitat for brown trout in Lar National Park seems likely. The management options to increase the climate change resilience of the streams have been suggested. Thermal habitat modeling appears to be a very useful tool for the assessment of climate warming effects on fish habitats in rivers and can be adopted to other streams in the region with marginal expenses.