Assessment of the influence of abiotic environmental factors on the distribution of bream and carp in the Northern Caspian

Abstract

Changing habitat conditions is an important driving force affecting the distribution of fish in the range. A quantitative assessment was made of the influence of environmental factors on the distribution of bream Abramis brama Linnaeus, 1758 and carp Cyprinus carpio Linnaeus, 1758 in the waters of the eastern part of the Northern Caspian. The number was estimated based on the results of research net catches. The preferred temperatures and habitat depths of bream and carp in the shallow zone of the Northern Caspian are shown. The colleof field material was carried out during complex expedition observations in 2014 and 2020. The installation of nets with a mesh of 30–200 mm was carried out in the shallow-water zone of the eastern part of the Northern Caspian. Bream and carp in the Northern Caspian Sea form concentrations in areas with depths up to 6–8 m. In the time interval from the end of April to October, bream was observed in the temperature range from 7.0 to 28.5 °C, carp — from 5.5 to 28.0 °C. A mathematical assessment of the influence of depth, temperature and water transparency on the number of these fish species was carried out. The obtained regression models took into account from 44.9 to 80.1% of the factors determining the number of fish in the studied water area. Carp are more sensitive to the effects of temperature, depth and transparency compared to bream. The obtained results provide a theoretical basis for predicting changes in the habitat of fish due to abiotic environmental factors, which is relevant in connection with pronounced climatic changes