The article describes the results of studies of the nocturnal migratory complex (NMC) of aquatic organisms in the coastal pelagic zone of the Lake Baikal in July 2017 at 8 sites different in environmental conditions, at depths from 5 to 17 m. Along with the traditional samples using plankton net and bottom grab held remote underwater video observation according to the original methodology. NMC is composed by benthic amphipods during nights pop-up in the pelagial, obligate pelagic amphipods Macrohectopus branickii (Dyb.) and juvenile fish (mainly from the Cottoidei suborder). There is an increase in the quantitative abundance of amphipods in the composition of NMC both in areas exposed to anthropogenic impact and in areas remote from its sources. Near the Cape of Omagachan, away from any settlements, the number of benthic amphipods in the NMC has increased 15.2% over the period from 2004 to 2006 and 9.4 times for 2006–2017. In the area opposite the village of Klyuevka (Southern Baikal) the number of floating amphipods in the field of view of the camera reached extremely high values – up to 250–350 specimens in the freeze frame, for the period 2014–2017 it increased 4 times. Most likely, this is one of the consequences of eutrophication of the lake, which is happening now. In the bays Aya and Zama in the composition of NMC was dominated by juvenile fish, which formed the different density concentrations at different depths. Relatively poor NMC marked bays Ongokon (Chivyrkuisky Bay) and Davsha (Northern Baikal), where the number of swimming amphipods in the frame did not exceed 37 to 45 and from 22 to 24 specimens, respectively. The taxonomic composition of amphipods in NMC and in the benthic community is almost completely different at the same time of research. In nocturnal migratory aggregations, a significant role belongs to the semi-pelagic species Micruropus wohlii platycercus (Dyb.), although its abundance varies greatly in different areas, and sometimes it is absent in nocturnal clusters (Zama Bay). In the Bay Senogda under the influence of the closely located city of Severobaikalsk, revealed abundant migratory complex with dominance of the species Micruropus talitroides (Dyb.). For the first time, larvae and pupae of Chironomidae were recorded in NMC. Pelagic amphipoda M. branickii was regularly observed in the coastal zone, in the area of the village Klyuevka its number in the summer in coastal NMC also increased 9.6 times over the period 2014–2017. Remote underwater video observations for NMC is an effective method of basic environmental monitoring of large aquatic ecosystems, they allow you to track changes in the trophic status of the reservoir at the level of organisms-consuments.

Batranin Dmitry Aleksandrovich, Student, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, tel.: (3952) 24–19–27, e-mail: badmal3477@gmail.com 

Takhteev Vadim Victorovich, Doctor of Sciences (Biology), Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, Baikal Museum ISC SB RAS, 1, Akademicheskaya St., Listvyanka settl., Irkutsk region, 664520, Russian Federation, tel.: (3952) 24–19–27, e-mail: Amphipoda@yandex.ru 

Eropova Irina Olegovna, Engineer, Assistant, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, tel.: (3952) 24–19–27, Postgraduate, Baikal Museum ISC SB RAS, 1, Akademicheskaya St., Listvyanka settl., Irkutsk region, 664520, Russian Federation, tel.: (3952) 45–31–45, e-mail: eropova.irina@yandex.ru 

Govorukhina Ekaterina Borisovna, Candidate of Science (Biology), Associate Professor, Irkutsk State University, 1, K. Marx St., Irkutsk, 664003, Russian Federation, tel.: (3952) 42–64–17, e-mail: kgovoruhina@mail.ru

Batranin D.A., Takhteev V.V., Eropova I.O., Govorukhina E.B. Structure of the Nocturnal Migratory Complex of Hydrobionts in Different Parts of Lake Baikal in the Summer of 2017 and the Problem of the Changes in the Trophic Status of the Lake. The Bulletin of Irkutsk State University. Series Biology. Ecology, 2019, vol. 27, pp. 62-86. https://doi.org/10.26516/2073-3372.2019.27.62 (in Russian)

Baikal Lake, underwater video surveillance, nocturnal migratory complex, amphipods, fishes, Macrohectopus branickii, quantitative abundance, eutrophication

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