Current status of aquatic biological resources in the middle and lower parts of the Amur River basin, including Lake Khanka and the Amursky Liman, is assessed. Generally high abundance of the water organisms is noted, but a downward trend is revealed. In 2015–2019, the total annual catch in the basin by Russian fishermen changed between 15.9–69.6 . 103 t (on average 39.1 . 103 t), with the main portions of pacific salmons (31.9 . 103 t, or 81.6 % of total catch) and smelts (5.5 . 103 t, 14.1 %). After the peak in 2016, the salmons abundance in the Amur has decreased, particularly for summer chum salmon and pink salmon, the number of arctic rainbow smelt Osmerus dentex has decreased gradually in the last 3 years. The stocks of freshwater fish are generally stable, with a slight increase for some species. The program of fisheries research «Amur River Fishes» implemented for 2020–2024 includes intensifying of traditional monitoring of the stocks and their biological state, as well as organization of detailed comprehensive studies for key species. Improvement of data quality on status of the main stocks of pacific salmons, smelts, and freshwater fishes is planned, as the basis for fisheries forecasting. Besides, the program conducts quantitative assessment of the main components of the ecosystem (phyto- and zooplankton, macrozoobenthos, and fish) and their dependence on environmental changes. State of food base for the Amur fish will be evaluated, including the feeding of artificially reproduced juveniles of salmons and sturgeons. Results of these studies will allow to improve approaches to regulation of fishery and to promote development of fishery industry toward organization of effective fishery complex in the Amur River basin.

Experience of pacific salmon artificial reproduction is discussed. Generalized data on juveniles (mostly fall chum salmon) release from hatcheries in the Amur River basin are presented. Information about the fish eggs origin (collection points) and transportation to incubation is provided. Some local features of salmon hatcheries are noted. Thus, the hatcheries in the middle Amur (Teplovsky and Bijansky) used previously the eggs collected in local tributaries of the Amur but recently, in conditions of low abundance of spawners, they transfer the eggs for incubation from fish farms located in the lower Amur. On the contrary, the hatcheries in the lower Amur (Udinsky, Gursky, and Anyuisky) collected the eggs in many dispersed sites in the beginning of their exploitation, but later, when local herds of artificial origin had appeared, they collected the eggs from producers coming to the hatcheries. This experience of eggs collection in dispersed temporary sites could be useful for periods of low stocks of pacific salmons in the Amur basin. The last such period started in 2017, so the fishery officials, as the Amur branch of Glavrybvod, can use this approach. Large transfers of chum eggs within the basin and from other rivers of the Okhotsk Sea and Japan Sea basins, presumably could affect genetic diversity, population structure and gene pool of this species. First results on evaluation efficiency of salmon hatcheries are discussed on the data of otolith marking started in 2015. Negative dependence of chum salmon catch on release of their juveniles is found: increasing of the juveniles output does not provide higher catches. Besides, the number of producers returned to hatcheries does not depend on the number of juveniles released from these hatcheries in the past, but corresponds with general dynamics of salmon stocks in the entire Amur basin. We believe that returns of chum salmon of wild and artificial origin have similar changes caused by same factors influencing on fish in the river and marine periods of their life.

Trawl fishery of shrimps Sclerocrangon salebrosa and Argis lar in the Sakhalin Bay of the Okhotsk Sea has started in 2014 and develops rapidly. Meanwhile, spatial distribution of these species is not known well and their biology and stock dynamics are not studied. State of the fishery and distribution patterns of S. salebrosa and A. lar in the northwestern Okhotsk Sea are investigated on the data collected by the authors aboaed commercial fishing vessels and in the accounting trawl survey conducted aboard RV Dmitry Peskov in summer of 2019, as well as some features of their biology are considered. In total, 542 commercial trawl catches collected in 2015–2019 with horizontal opening 36 m from the depth of 39–140 m and 147 trawl catches collected during the survey with horizontal opening 16 m from the depth of 11–321 m are analyzed; 21,590 shrimp specimens caught within the period from June 23 to November 2 are examined. During 2014–2019, the number of shrimp fishing vessels in the Sakhalin Bay has increased from 1 to 6, their annual landing — from 78.7 to 642.0 t (376 t of S. salebrosa and 266 t of A. lar in 2019). Their mean catch per unit effort varied from 48 to 108 kg/hr of trawling for S. salebrosa and from 40 to 87 kg/hr for A. lar, with the average catch per trawling 379 and 346 kg, and average daily catch 1380 and 1144 kg, respectively. Night catches of S. salebrosa were in 2.7 times higher than the daily catches, on average (104.7 ± 45.7 kg/hr vs 39.1 ± 31.8 kg/hr); night catches of A. lar were in 2.0 times higher than the daily catches (80.2 ± 39.0 kg/hr vs 39.6 ± 34.2 kg/hr). Portion of A. lar in the summary catches of two species varied from 4 to 88 %, on average 48 %; besides, by-catch of fish (flounders, saffron cod, pollock, cod, sculpins, herring) and humpy shrimp Pandalus goniurus was considerable. So, the portion of the most valuable species (sculptured shrimp S. salebrosa) did not exceed ⅓ of the total catch, on average. The actual annual catches exceeded significantly the recommended volumes in 2017–2019, up to 164 % for S. salebrosa and 156 % for A. lar. According to results of the trawl survey in 2019, spatial distribution patterns for S. salebrosa and A. lar coincide in details in the northern Okhotsk Sea: both species are distributed at the depth between 20–145 m, with the densest aggregations (> 60 % of both stocks) located between Bolshoi Shantar Island and the northern tip of Sakhalin, southward from 55о 30′ N, where their biomasses reach 434 kg/km² for S. salebrosa and 68 kg/km2 for A. lar. Total commercial stocks of these species within the North Okhotsk Sea fishery district were assessed in 2019 as 16.0 . 103 t for S. salebrosa and 3.8 . 103 t for A. lar. Reproductive cycles of S. salebrosa and A. lar females in the Okhotsk Sea are fundamentally the same as the cycle of former species in Peter the Great Bay (Japan Sea), with their total duration of 48 months including 24 months for the gonads development until spawning and 24 months from the spawning to hatching of larvae. In the Okhotsk Sea, spawning of S. salebrosa and A. lar occurs most likely in spring; mass hatching of their larvae — in summer.

Linear and weight growth of pike perch in the Amur River estuary is considered using the data on age determined for 197 specimens. The growth is described by von Bertalanffy and Schmalhausen equations. Some biological parameters of pike perch as the maximum size, age of mass maturation, etc. are calculated using the age-differentiated coefficients of natural mortality. The growth and biological parameters of pike perch in the Amur estuary are compared with the same parameters of this species in the Amur River at Khabarovsk. Recently 3 ecological forms of pike perch are distinguished in the Amur basin: i) riverine ecotype self-redistributed from Lake Khanka, ii) lacustrine ecotype in the lower Amur River, and iii) highly productive semi-anadromous marime ecotype in the Amur estuary. The 3^rd phase of pike perch acclimatization is observed now in the Amur estuary known as the «bloom» phase accompanied with prominent increasing of population abundance and individual growth rate acceleration. Pike perch prey in this area mainly on juveniles of non-anadromous and diadromous fish, or on pond smelt Hypomesus olidus during their concentration in the estuary in winter.

Data on commercial catches of japanese flying squid Todarodes pacificus in the northwestern Tatar Strait in 2003–2019 are analyzed. To assess the resours status in the study area, the relative number (individuals per jigger winch per hour) and biomass (kilograms per vessel per day) marks recognized to be the most applicable winch per hour or the catch in kg per vessel per day. The average CPUE value was 35.6 ± 3.6 ind./winch/hour; increasing trend of CPUE is observed (α = 1.5 ± 0.6, r² = 0.3, p < 0.03). The squid abundance decreased slightly in the last 2 years, with CPUE decreasing to 28 ind./winch/hour in 2019, though the squid biomass was relatively stable (average CPUE 582.0 ± 45.8 kg/vessel/day) — decreased number of caught individuals was compensated by individual body weight increasing. Long-term tendency to the body weight increasing was noted: the average body weight was 205.0 ± 4.0 g in 2004, 256.0 ± 3.5 g in 2012, and 297.0 ± 6.3 g in 2019. Possible climate change influence on the squid population was discussed. Because of warming in the reproductive area of T. pacificus in the southern Japan Sea, SST in the spawning period reached 20–25 ^оC and exceeded the value optimal for reproduction and larvae development (15–23 ^оC), so the squid abundance decreased. On the contrary, in the northern Japan Sea (in the Tatar Strait) the warming caused better conditions for the squid feeding: the higher zooplankton biomass in this area was observed under SST 13–18 ^оC that is reached every year recently. On the other hand, the Tsushima Current intensifying promoted active migrations of T. pacificus to the northwestern Tatar Strait. These factors of climate warming ensure favorable environments for northward migrations of T. pacificus and forming of dense feeding aggregations in the northwestern Tatar Strait that allows to expect good conditions for the squid fishery in this area in the nearest future.

Dependence of chum salmon Oncorhynchus keta recruitment (number of mature adults) in Okhotsky district located on the Okhotsk Sea coast on a number of spawners is analyzed for the spawning years of 1983–2014. During this period, the progeny abundance increased, then stabilized on a high level, then decreased. Generally, the number of recruits depended poorly on the number of spawners because of clear environmental impact. Indeed, the recruitment variation could be simulated on the base of Ricker curve with addition of a variable responsible for environmental trend. Number of the year of spawning was used as such variable. So, the chum recruitment R is modeled as R = a. P. exp(–(P/b + ((X – c)/d)² )) for the period of increasing and R = a. P. exp(–(P/b – ((X – c)/с)² )) for the period of decreasing, where P — number of parents, X — year of spawning, and a, b, c, d — empirical coefficients. This model explains > 80 % of the recruitment deviation. The environmental impact was weak in the period of stable recruitment, so the direct dependence of progeny abundance on spawners number (Ricker curve) can be used for these years, with similar determination (r² > 0.8). This approach is proposed as a possible compromise between hypotheses on climate-driven and autoregulating mechanisms of the salmons abundance variability.

Data on quantitative distribution of early and late spawners of sockeye salmon in the Lake Nachikinskoye basin were collected in 2019 using quadcopter. Features of sockeye spawning in certain sectors of the lake coast and at the spawning stations are analyzed. The spawning starts earlier on the eastern coast, and then on the western coast. The late sockeye spawning is considered in details at the spawning stations on littoral shelves, on steep coastal slopes, in key limnocrenes, in algae fields at the depths up to 5 m, and in the river tributaries. Environmental conditions of the stations are compared quantitatively by several parameters, as water flows and their gradients, water temperature, dissolved oxygen content, soils composition, impact of predators and waves. Each station has its advantages and disadvantages. The lake shallows dominate among the spawning grounds, but their diversity provides stability and even growth of local sockeye salmon stocks. Spatial distribution of the sockeye spawning grounds is described. The number of spawned fish is assessed using the trapezoid approximation (TAUC) as 55 . 103 ind. for early sockeye and 132 . 103 ind. for late sockeye that shows a considerable growth of the stocks of sockeye salmon in Lake Nachikinskoye since the middle of last century.

General patterns of bivalves distribution by depth in the northwestern Tatar Strait (within Khabarovsk region) are analyzed on the data of 384 trawl, 573 drag, and 1177 diving stations during research surveys in 2003–2016 where the samples were collected with commonly accepted methods. Depths from 0 to 600 m were surveyed. Besides, scientific publications and archival materials related to this area were taken into account. The species richness (y) decreases with depth (x) exponentially from 51 species at 1–20 m to 3 species at 400–600 m that could be approximated satisfactory by the equation y = 31.799. e^–0.0502x (r² = 0.89). Sublittoral and bathial faunas can be separated by cluster analysis of special composition in the depth range 0–150 m and 150–600 m, respectively, with similarity of 0.11 between them. Within these boundaries, 5 local faunas are distinguished: I (< 2 m, the surf zone at the upper boundary of the sublittoral zone), II (2–30 m, the upper sublittoral zone), III (30–150 m, the lower sublittoral zone), IV (150–400 m, the transitional zone) and V (400–600 m, the upper bathyal zone), with similarity between them from 0.14 to 0.36. The upper sublittoral zone has the maximum species richness — 64 species and is the habitat for a «core» of Bivalve fauna with almost ⅔ of its species, preserving the ratio of the main biogeographic groups typical for the researched area. Commercial fishery of scallop Mizuhopecten yessoensis exploited this zone mainly and now is banned to prevent reduction of its stock. Other commercial bivalves, as Callista brevisiphonata, Serripes laperousii, Keenocardium californiense, and Mercenaria stimpsoni, which commercial stocks are estimated in order of 10⁵ t, are also concentrated in this zone but are not landed currently. Portion of moderately cold-water species (wide-boreal and low-boreal) increases and portion of warm-water species (subtropical-boreal and subtropical-low-boreal) decreases with depth, with the slope coefficients of the regressions α = 9.2 ± 4.1 (p = 0.11) and α = –9.6 ± 2.3 (p = 0.03), respectively. The coldwater species are absent in the surf and upper bathyal zones but their portion in other zones is 20–26 %. Rather high portion of boreal-arctic species on shallow depths reflects relative severity of the northwestern Tatar Strait that is the most cold-water area of the Japan Sea. The warm-water species are completely absent in the upper bathyal zone, i.e. at the depths > 400 m. On the other hand, portion of banal species increases and portion of specific species decreases with depth, also portion of rare species increases and portion of mass species decreases with depth, with the slope coefficients α = 9.10 ± 0.49 (p = 0.0003) and α = –4.5 ± 2.5 (p = 0.01), respectively. Vertical distribution of frequent species is rather uniform: 33–57 %. These patterns of the species distribution by zones almost do not change spatially: distribution of different biogeographic groups of species in three coastal areas (47–49^о N, 49–51^о N, and > 51^о N) has no statistically significant differences. Distribution of species richness and composition by depth ranges relates to ecotopic variation (74 % of diversity), to the degree of exploration (22 %), and to the influence of such complex factor as a depth (4 %). Further faunistic studies are recommended in the most diverse areas, as bays, harbours, and capes vicinities with variable grounds and submarine vegetation, in all available depth ranges. Such surveys can provide faunistically representative information on the species wealth. The list of Bivalve mollusk species for the northwestern Tatar Strait can be enlarged possibly in 1/5 if detailed studies of their fauna will be conducted. The fauna on great depths is the most underexplored. The total expected number of bivalve species in this area is at least 120.

In this paper we have analyzed an approach to assessing the relationship between some characteristics of the net panels forming the rope/net cone of a fishing trawl. Using the mathematical relationship of solidity ratios for the rope/net panels, it is possible to analyze existing structures and, furthermore, reduce the time for selecting the prototype trawl. Such mathematical relationship allows faster calculation of new trawl designs which takes into account the production specifics of an enterprise manufacturing the trawl fishing gear. The use of mathematical relationships provides the opportunity to accelerate the process of trawl construction.

Method of acoustic tagging of large-sized fish in a medium river is successfully tested for the case of siberian taimen Hucho taimen in the Tugur River. Algorithm of fish anesthesia and acoustic tag input into its body cavity is developed. For successful tagging, total duration of the process, including anesthesia, should not exceed 5 minutes. The best results of tagging are obtained for fish with a body length of 110–130 cm, which tolerate anesthesia easily. In 2017–2019, 25 out of 29 tagged fish were registered by acoustic equipment that indicates high efficiency of the method (86.2 %). Distance from the release point to the point of tag registration varied from 0.2 to 39.8 km. Some fish crossed almost completely the buoy-controlled section of the river that indicates a rather high migration potential of siberian taimen. On the background of high individual diversity of migration activity, two principally different behavioral strategies are distinguished — «residents» staying in one place up to 2 months and «nomads» migrating to a distance up to 30 km per day. The radius of taimen migration increases usually in May and September and decreases in August. The seasonal increasing is associated with feeding migrations: taimen feed on downstream juveniles of chum salmon Oncorhynchus keta and prespawning minnows Rhynchocypris lagowskii in May and on chum adults migrating to spawning grounds in September. During twilight and at night, the migrations are usually more active, but they are less visible and shorter in the morning and afternoon. Correspondingly, the main feeding of taimen is assumed in the twilight and dark time, whereas a supporting feeding in the daytime.

Microchemical analysis of calcified structures of fish is a modern technique for determining the origin of fish species and ontogenetic reconstructions of their habitat that can be applied for such tasks as stocks separation in mixed samples, tracking of fish migrations, determining of spawning, feeding or wintering areas, differentiation of fish of artificial and natural origin, growth analysis, age evaluation, etc. The approach is based on analysis of trace elements concentration between the center and periphery of a calcified structure, or precise measurement of the elements and their isotopes concentration in certain sites of sample. The calcified structures most often used for analysis are otoliths, skeleton bones, scales, and also statoliths of lampreys or beaks and statoliths of cephalopods. Specifics of the method application are described with examples of its use for solving diverse tasks of fundamental and applied science, in particular in complex studies of biological resources in the Amur River basin.

 Inventory of spawning grounds is an important tool for estimation of pacific salmons abundance and adequate management of their stocks. A set of the most up-to-date, relevant and effective methods based upon geographic information system (GIS) is substantiated, designed, developed and scheduled to implementation for inventory of the spawning grounds in the Amur basin. Abilities of GIS-technologies for optimization of the surveys planning and conducting and for processing, analysis, visualization and presentation of their results due to accelerated, simplified and enhanced workflow are shown. Three components of modern corporative GIS are presented: server, desktop and mobile ones. The system is partially loaded with the data about spawning grounds, tested for the basic operations as data collection, multi-user editing, geoprocessing, spatial analysis, cartographic visualization, protected web publication, etc., and adjusted and improved using the results of this testing for further implementation in complex fisheries surveys in the Amur River basin. Proposed GIS-technology is modifiable and scalable, so can be spread to other species and areas after appropriate modification; the GIS can be specialized for certain practical tasks.

A simple and cost-effective method for macrophyte stock assessment as visual survey, was tested. It demonstrated good efficiency for counting of Saccharina japonica. The method is based on visual evaluation of SAV projective cover. Such subjective data should be verified. For this purpose, the projective cover along the Tatar Strait coast was estimated independently by two observers. In total, 125 km of the coastline was surveyed with 322 parallel visual estimations at 81 stations. The estimations of both observers agreed well: the concordance coefficient was 0.73 for the total projective cover and 0.78 for the projective cover of S. japonica, at p < 0.0001. About 81 % of the total projective cover and 82 % of S. japonica projective cover were counted with high coherency, whereas poor coherency was noted for < 3 % of both parameters. Average difference between estimations of two observers was 0.083 ± 0.012 for the total projective cover and 0.090 ± 0.012 for S. japonica projective cover. However, comparison of the visual estimations from the sea surface with the SCUBA estimations made near the bottom showed that surface observations resulted in some underestimation of the total projective cover, though the difference was statistically insignificant (p = 0.68). The near-bottom SCUBA survey provides better assessment for small and cortical algae (Ralfsiales and partially Corallinales). Commercial stock of S. japonica was calculated using previously reported relationship between biomass and projective cover (r² = 0.81). The stock estimations for certain areas on the data of two observers had no statistically significant differences (p = 0.46–0.80, depending on the criteria used), the total stock estimations were also very close (34 and 36 thousand tons for total stock and 26 and 24 thousand tons for its commercial part). The visual observations are useful for revealing general features of the vegetation spatial distribution. Linear regressions parameters of the algae abundance on latitude for the data of both observers were similar. They had the angular coefficients –0.13 ± 0.07 and –0.10 ± 0.07 for the total projective cover and –0.25 ± 0.07 and –0.23 ± 0.06 for S. japonica projective cover. In the southern part of survey, the average total projective cover was 0.59 ± 0.04, while it was slightly lower in the northern part: 0.53 ± 0.04; the same estimations for the projective cover of S. japonica differed more considerable: 0.49 ± 0.04 and 0.24 ± 0.03, respectively. There is concluded that the visual surveys of macrophytes are economically effective and allow to reduce labor efforts significantly, comparing with traditional SCUBA surveys (working time in 101 times, costs in 103 times). The video recording ensures the data verification by outside experts, as in the cases when observers cannot identify some species. However, capability of this method is limited by high water turbidity and other cases of worsened visibility. For successful implementation of visual surveys, its algorithm for various environmental conditions is developed and supplemented with necessary instructions.

Dominant species are identified at infracenotic level for aquatic vegetation in the sublittoral zone of the northwestern Tatar Strait (Japan Sea) on the data collected in 2010–2019. Seven different methods of the identifying are considered based both on visual qualitative and quantitative assessments and on instrumental estimations of abundance for 44 macrophyte species. Depending on applied method, 19–25 species (7–22 % of total number of species) are identified as the dominants, including 10 species identified by all methods. List of these 10 species is defined as the core of vegetation that determines its general properties and the species are determined as unconditional dominants, in opposite to other ones identified by at least one method — conditional dominants. All macrophyte species in areas of low abundance do not meet the dominance criteria. All lists of dominants, including those based on visual estimates of projective cover and its physiognomy, are statistically indistinguishable (p = 0.55–0.92, by pairs of lists) and highly similar (Bray-Curtis index 0.80–0.95, Jacquard index 0.65–0.87), with one exception for the list identified by the method of ranking for the average projective cover (indices of similarity with other lists: 0.68–0.71 by Bray-Curtis, 0.46–0.56 by Jacquard). This visual method of projective cover assessment is combined with the procedure of species dividing to dominant and non-dominant groups. Quantitative criteria of projective cover and biomass, by species (thresholds 0.2 and 1.0 kg/m³, respectively) are used for dividing on cenotic and landscape levels and ranking with Brotskaya-Zenkevich index and its modification for projective cover is used for dividing on regional level. Visual methods are available for verification, but the lists of dominants based on visual and instrumental assessments should be mutually verified.