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Biological diversity is the basis for, and an indicator of biosphere integrity. Together with climate change, its loss is one of the two most important planetary boundaries. A halt in biodiversity loss is one of the UN Sustainable Development Goals. Current changes in biodiversity in the vast landmass of Siberia are at an initial stage of inventory, even though the Siberian environment is experiencing rapid climate change, weather extremes and transformation of land use and management. Biodiversity changes affect traditional land use by Indigenous People and multiple ecosystem services with implications for local and national economies. Here we review and analyse a large number of scientific publications, which are little known outside Russia, and we provide insights into Siberian biodiversity issues for the wider international research community. Case studies are presented on biodiversity changes for insect pests, fish, amphibians and reptiles, birds, mammals and steppe vegetation, and we discuss their causes and consequences. SUPPLEMENTARY INFORMATION: The online version of this article (10.1007/s13280-021-01570-6) contains supplementary material, which is available to authorized users.

Information about some features of the Prussian carp Carassius gibelio (Bloch, 1782) in three different floodplain lakes in the Middle Ob river basin are presented. Individuals of younger age groups predominate in populations. Fish over the age of 9+ are not noted. The ratio of females to males is different, from 4:1 to 8:1, always in favor of females, which is typical for Prussian carp populations in Western Siberia. There were specimens in the sample from 152 to 355 mm long and weighing from 115 to 1250 g. When comparing males and females of the same age, the latter are generally larger. The noted size characteristics — 335 mm and 1250 g — are the maximum of the published data for Prussian carp Carassius gibelio in the Middle Ob river basin. When comparing individuals of the same age, it was shown that Prussian carp Carassius gibelio is a larger size in the big not-frozen lake Monatka than in the small, frozen lakes Zmeevo and Taskino. The maturity of female Prussian carp Carassius gibelio in floodplain lakes of the Middle Ob river basin occurs at the age of 3+, but some 2+ were mature. At the age of 4+, all specimens in the samples were sexually mature. Sexual dimorphism Prussian carp from lake Monatka is weakly expressed: in males, the length of the head, the height of the dorsal and the length of the pectoral fins are statistically significantly greater. A higher dorsal fin can be considered a characteristic feature of the male Prussian carp in the south of Western Siberia in comparison with the females.

The data on the catch, age composition and growth of the roach Rutilus rutilus L. in commercial herd in the Middle Ob basin (in the Tomsk region) are presented. It is shown that the catches of the roach in the middle of the 20th century were 2098 tons per year. In the second half of the 1960s, they fell sharply by more than two times. It was caused by a decrease in the areas of effective spawning due to the reduction of runoff in the Ob during spring floods as a result of the regulation of the level regime by the dam of the Novosibirsk hydroelectric power station. After that, the catch of roach remained at about 1013 tons per year until the beginning of economic reforms in the country, when the catch of this species became unprofitable, as a result of which catches decreased to an average of 436 tons per year. Currently, the basis of commercial catches is made up of roach with a commercial length of 140 to 210 mm and a weight of 50 to 150 g at the age of 2+...5+. It is noted, compared with the 1970–1980s, there is a shift in the age series towards an increase in the value of older age groups, which may indicate underutilization of the stock of the roach. The statistically significant positive relationship between catches of roach and the average duration of flooding of the floodplain in the years of the occurrence of generations that form the basis of catches was revealed. Prolonged floods also provide better conditions for fish feeding (a statistically significant positive relationship between the mass of fish of the same age and the duration of flooding of the floodplain is shown). Thus, the hydrological regime in the spring has a decisive influence on the state of the stocks of roach in the Middle Ob.

Data are presented on fish community structure in ponds and floodplain and mainland lakes in the southern taiga subzone of Western Siberia (within Tomsk region), where a total of 14 fish species have been recorded. The ordering of data on the fish biomass using a factor classification program has allowed us to distinguish three population groups, with one of them including three subgroups. Winter hypoxia is the most important among external factors determining the structure of fish communities. Its absence determines the presence of perch in the fish communities; in turn, the abundance of perch affects the abundance of other fish species. Therefore, the primary organization of the communities is determined by the environment and their secondary organization by the relationships between the species.

The data on feeding of the Amur sleeper Perccottus glenii in a pond located in the southern taiga subzone in West Siberia obtained in May–October 2017 are presented. A total of 15 components have been identified in its guts. The diet of Amur sleeper is largely composed of larvae of amphibiotic insects and amphibians in spring and fish in summer and autumn periods; the diversity of food composition decreases by autumn.

A biogeographical division of northern Eurasia (within the USSR borders as of 1991) based on cluster analysis of the cyclostome and fish fauna composition at 597 sites listed in the Biodat database has been performed. The classification based on the Jaccard similarity coefficients included two regions, 12 subregions, eight provinces, and 11 districts. The division performed explained 67% of the variance of the similarity coefficients, this being 21% higher than the respective value for an earlier scheme (Berg, 1962) that covered a significantly greater territory. Correlation with the climatic regimes and environmental factors identified could explain 82% of fish fauna heterogeneity (the multiple coefficient of correlation was 0.91). The nonorthogonal relations with the temperature regime (67% of the variance of similarity coefficients), landscape and climatic zoning (58%), location within a specific river basin (57%), and provinciality (30%) were the most important factors.

The paper contains a complete annotated list of freshwater ichthyofauna of the Middle Ob River basin. The list is based on an analysis of publications and on the results of the authors’ research, and it includes 43 species in two classes, 9 orders, 12 families, and 30 genera. Ten of all listed species are introduced and only seven are naturalized. For each species, taxonomic comments are provided where necessary and conservation status, distribution within the Middle Ob River basin, abundance and commercial value are indicated. Latin and English names are given.

The sterlet (Acipenser ruthenus Linnaeus, 1758) is a relatively small sturgeon widely distributed in Eurasian rivers from the Danube to the Yenisei. During the twentieth century, all wild sterlet populations have declined due to anthropogenic factors including: overfishing, poaching, construction of dams, and pollution. Despite the necessity of characterization both wild and captive stocks, few studies of population genetics have been performed thus far. Here we studied the genetic diversity and geographic structure of sterlet populations across the eastern range – Ob-Irtysh and Yenisei basins – by sequencing a 628-bp fragment of mitochondrial DNA control region. We identified 98 new haplotypes, delineated 12 haplogroups and estimated the time of basal haplogroup divergence within the species as over 8 million years ago. Our data suggest that Ob-Irtysh and Yenisei populations are isolated from each other and much lower genetic diversity is present in the Yenisei population than in the Ob-Irtysh population. Our data imply that sterlet populations in Siberian rivers underwent bottleneck or fragmentation, followed by subsequent population expansion. The data obtained here are important for sterlet population monitoring and restocking management.

To date, 22 alien fish species are known in the Ob River basin. Of them, nine species—Pike-perch Sander lucioperca, Freshwater bream Abramis brama, common carp Cyprinus carpio, belica Leucaspius delineatus, bleak Alburnus alburnus, Stone moroko Pseudorasbora parva, Amur sleeper Perccottus glenii, Nikolsky’s loach Misgurnus nikolskyi, and southern ninespine stickleback Pungitius platygaster—formed self-reproducing populations and started self-spreading in natural waterbodies. This paper summarizes the data on invasion of alien fish species in the Ob River basin. The data on history, rate of spread, modern distribution, and relative abundance are given. It is shown that water temperature is the main environmental factor which limits the expansion of introduced species in the Ob basin.

The data show quantitative and qualitative composition of macrozoobenthos of the 12 left-bank confluences of the Middle Ob. The research has documented the presence of various groups, such as Oligohaeta, Diptera, Odonata, Hirudinea, Tabanidae, Trichoptera and Mollusca. The chironomids, molluscs and leeches play a significant role in the generation of biomass in the surveyed streams, and the abundance mostly depends on chironomids, oligochaetes and leeches. In general, zoobenthos abundance ranges from 8.8 (the Shudelka river) to 1839.9 (the Kochebilovka river) ind./m2, biomass is from 0.08 (Tatosh river) to 8.37 (Lozunga river) g/m2. The amount and benthos biomass of the Middle Ob’s second-order tributaries is higher than in the first-order tributaries.

Data on the species composition of the fish population inhabiting the tributaries of the Novosibirsk reservoir are given in the article. The structure of fish communities and possible environmental factors determining it have been revealed. The relation between the heterogeneity of fish communities and the river depth and length, relief, current velocity, floodplain, and estuarial areas, presence of sand-pebble shallow waters and channel order, has been studied.