BIOLOGICAL RESOURCES
Dredgе survey (177 stations) was conducted in the northwestern Tatar Strait (northward from 48° N) at the depths 14–82 m in summer 2018 (from July 21 to August 7). In the dredge catches, 76 species and taxa of benthic invertebrates are recorded, including 42 epibenthic species, mainly Ophiura sarsi, Evasterias echinosoma, Strongylocentrotus pallidus, Paralithodes brevipes, Cucumaria japonica, P. camtschaticus, Mizuhopecten yessoensis, and S. intermedius. The areas of their aggregations are determined. The largest area was occupied by the settlements of polyphagous S. pallidus (5100 km22 at the depths 30–60 m). Specific biomass of epibenthos is calculated, its average value within the surveyed area was 21.5 ± 2.0 g/m2. Depth ranges of the species domination are defined. The dominant species changed with latitude: in the southern part of the survey, Paralithodes camtschaticus dominated with the biomass of 5.1 ± 4.4 g/m2 in the upper 20 m layer (48–49° N), replaced at the depth of 20–30 m by P. brevipes (22.2 ± 14.2 g/m2 between 48–49° N) or C. japonica (28.2 ± 3.0 g/m2 between 49–50° N), both species changed deeper to S. pallidus (4.3 ± 1.1 g/m2); in the northern part of the survey (50–51° N), S. intermedius dominated in the upper 30 m layer with the biomass of 14.7 ± 9.5 g/m2, Mizuhopecten yessoensis (9.7 ± 6.2 g/m2 ) and Evasterias echinosoma (5.1 ± 1,0 g/m2 ) prevailed in the depth range of 30–40 m and were replaced by S. pallidus (18.0 ± 9.5 g/m2) below 50 m; in the northernmost shallow tip of the Strait, Ophiura sarsi dominated absolutely with the biomass of 13.0 ± 1.1 g/m2) in the whole depth range down to 30 m. The greatest species richness and abundance of epibenthos were observed at the depths not exceeding 40 m. Statistically significant decreasing of quantitative parameters of the epibenthos with the depth is observed because of the bottom temperature and topical diversity declination with depth. However, environmental conditions have no significant impact on latitudinal distribution of abundance, wealth and species diversity of the epifauna in the surveyed area. The grouping of epibenthos with specific species structure that could be classified as the circumlittoral one is defined in the upper shelf zone in the northernmost area with the depth < 30 m (somewhere < 40 m).
Data on biology, ecology and fishery of asiatic smelt in the Uda River during its spawning migration are analyzed. The spawning begins in May-June in 2–11 km from the river mouth and lasts 3–10 days. Timing of its start varies from May 22 (2014 and 2018) to June 14 (2001), with 24 days difference. The spawning migration begins under the water temperature 6.0 оС, during the spawning the temperature varies from 6.2 to 11.9 оС. The river flow velocity on the spawning grounds is 1.2–2.6 m/s, the river depth varies from 0.3 to 2.5 m. Age of the spawners is 2–8 years, their length is 11.5–32.0 cm and weight 10.8–275.0 g, males usually prevail in number (63–81 %). Depending on the year-class strength, the fish in age of 3 or 4 years prevail among the spawners. After spawning, females leave the spawning grounds immediately — in that time their occurrence in the catches below the spawning grounds can reach 85 %. Size of the spawners decreases during the migration, for males the decreasing was from 19.0 to 15.0 cm in 2007, from 20.2 to 18.8 cm in 2014, from 19.3 to 16.6 cm in 2015, and from 19.4 to 16.0 cm in 2016, for females — from 21.0 to 18.0 cm in 2007, from 22.1 to 19.6 cm in 2014, from 21.3 to 19.0 cm in 2015, and from 24.5 to 16.1 cm in 2016. Annual increments of the smelt body length are 0.7–7.8 cm, on average 3.9 cm, for the body weight 17.1–39.9 g, on average 32.1 g. The minimum registered size of mature male and female was 11.5 and 13.0 cm, respectively. Percentage of the smelt with non-commercial size during spawning migration was 19.2 % in 2007, 0.4 % in 2014, 15.4 % in 2015, and 28.4 % in 2016. The group linear growth of asiatic smelt could be approximated by Bertalanffy equation: L = 30.5 [1 – e–0.317 (t – 0.533)]. Its body length dependence on weight is described by the equation of simple allometry: W = 0.002 L3.380 (determination r 2 = 0.92–0.99). The body weight depends on age as the function: Wt = 2.974t 2.136. Individual absolute fecundity of the smelt in the Uda varies from 11300 to 141300 eggs, on average 52500 eggs in 2016 and 50400 eggs in 2007; these values are close to the smelt fecundity in the Ulbeya and Inya rivers. The fecundity variation generally increases with the age: the registered ranges of absolute fecundity (thousand eggs) were, by age groups: 19.1 for 3 years, 53.5 for 4 years, 37.8 for 5 years, 57.5 for 6 years, and 60.3 for 7 years old fish, the ranges of relative fecundity (eggs/g of body weight) were: 864, 537, 565, 501, and 449 eggs/g for the same age groups. The total population fecundity was 32.7. 109 eggs in 2016. The individual absolute fecundity has the following dependencies on body length, weight, and age: AF(L) = 0.001 L3.437, AF(W) = 0.650 W0.986, and AF(t) = 1.661 t 2.250, respectively. The stock of asiatic smelt in the Uda is represented by migrating fish only. Its fishery was conducted by 8 companies, their total annual landing increased from 10 t in 2012 to 373 t in 2017 and slightly decreased recently: the mean landing for 2013–2019 was 276 t. The spawning biomass of smelt was estimated from 637 to 1734 t, by years, that was about 70 % of the biomass of mature smelt in the Shantar Sea.
In vitro morphological development of whitespotted greenling Hexagrammos stelleri from the northern Okhotsk Sea is described in detail and illustrated from the eggs fertilization to the larvae transition to exogenous feeding. Mean diameter of the fertilized eggs is determined as 2.03 mm (1.80–2.30 mm). The embryos hatch in 30 days and 6 hours after fertilization of eggs under the water temperature of 7.1–12.4 оC (on average 11.5 оC). The hatched prelarvae have the size TL 7.73–9.20 mm (on average 8.49 ± 0.09 mm) and SL 7.48–8.80 (8.15 ± 0.08 mm).
ENVIRONMENTS OF FISHERIES RESOURCES
AQUACULTURE
TECHNOLOGY FOR PROCESSING OF AQUATIC ORGANISMS,
METHODS OF INVESTIGATIONS
ISSN 2658-5510 (Online)