Vol. 78 2026

ARTICLES

Distribution and Population Parameters of Brown Trout Salmo Trutta Linnaeus, 1758 (Actinopterygii: Salmonidae) in West Aegean Basin in Bulgaria in Response to Hydromorphological Pressure and Climate Changes

Stefan Kazakov1*, Desislava Stoianova1, Apostolos Apostolou1, Boris Velkov1, Borislav Borisov2, Milena Pavlova1, Luchezar Pehlivanov1

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*1Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria; E-mail: skazakov.iber@gmail.com, d.st.stoianova@gmail.Com, apostolosfish@abv.bg, milena1pavlova@gmail.com, luchezarpehlivanov@gmail.com
2Geograf Ltd. Bulgaria; E-mail: bobiborisov@abv.bg

https://doi.org/10.71424/azb78.1.002849

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Abstract

The aim of the study was to assess the response of the brown trout (Salmo trutta) population as indicator of anthropogenic pressure and climate changes. About 239 samples from the watersheds of the rivers Struma, Mesta and Dospat, from Bulgarian territory were gathered and analysed for the period between 2009 and 2023. Fish-based index for ecological status assessment as well as trout population parameters like abundance, biomass and average weight were tested as dependent variable of the hydromorphological status of the Water Bodies (WBs). Air temperature was used as an indirect variable for analysis of the trout response to climate change. We build a habitat suitability model on river segment level using both variables measured during sampling, and variables extracted from publicly available GIS data.
Brown trout was found in 119 samples from 44 WBs (out of 168 WBs) in West Aegean Basin Directorate, representing 26% of the designated WBs in the region. The trout fish index, showed significant relation with two types of hydromorphological pressure: morphological modifications as well as water flow regulation. Higher temperatures, used as a proxy for climate change, were associated with reduced average individual trout weight according to general linear mixed model results. The habitat suitability model indicated that water depth and the proportion of forested areas in the catchment significantly influence the suitability of aquatic habitats for S. trutta in the analysed river segments.

Key words

trout rivers, resource fish species, habitat suitability model, anthropogenic pressure

How to Cite
Kazakov S., Stoianova D., Apostolou A., Velkov B., Borisov B., Pavlova M., Pehlivanov L. 2026. Distribution and population parameters of Brown Trout Salmo trutta Linnaeus, 1758 (Actinopterygii: Salmonidae) in West Aegean Basin in Bulgaria in response to hydromorphological pressure and climate changes. Acta zoologica bulgarica 78.

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