BIOLOGICAL RESOURCES
Data on juvenile pink salmon from the continental coast of the Okhotsk Sea obtained in 1960s–2010s are summarized. The timing and dynamics of their downstream migration are considered in terms of biological parameters and nutrition. Brief information on their early marine life is presented. The mass seaward migration of pink salmon begins when the river water is warmed to 2.5–4.0 оC. The juveniles migrate from rivers to the coastal marine waters diurnally. During the seaward migration, their body length and weight do not change significantly, as a rule, but a portion of fish with external feeding increases. Year-toyearly, in the rivers the portion of juveniles switched to external feeding is higher in the years with mild spring flood.
Long-term data on feeding migrations of hatchery pacific salmon (pink and chum salmon) in the Okhotsk Sea and adjacent Pacific waters in the autumn-winter of 2011–2021 are generalized. The study is based on materials (otolith samples, biological indices) collected in the trawl surveys conducted by TINRO, as well as on international statistics on releases and tagging of pacific salmon at the Russian and Japanese hatcheries. The main patterns of intraspecific structure, migration routes, spatial distribution, and volumes of catch are determined for these species, as well as the size-weight parameters of fish originated from different regions. Natural mortality of salmon juveniles at the stage of migration from the coastal zone to the open sea is estimated at systemic level for the first time.
Some parameters of the abundance dynamics for the pacific salmon of Russian origin are specified and volume of their possible catch are substantiated for the next decade. The average annual catch for 1907–2022 is amounted as 250 thousand tons. Cyclic variations were observed within this time with the intervals of 72 years between the minimal values and 75 years between the maximums. The high catches were landed during app. 35 years, and the low catches — during app. 40 years, so the periods of high and low abundance were approximately equal (35–40 years). The harvest runs occurred mostly in odd years; the dominant years (odd either even) changed usually when the abundance had increasing. The high level of abundance (> 250 . 103 t, not below of 200 . 103 t in the years of the worst run) is expected in the nearest decade, until the middle 2030s. After this period of high abundance, the stocks of domestic salmon will be insufficient for profitable commercial fishery on majority of existing fishing grounds.
Population dynamics and size-age structure are analyzed for the chum salmon herd formed in the Prostor and Kurilsky Bays of Iturup Island (Kuril Islands). Release of chum juveniles into the waters of the bays increased from 10.7.106 ind. in 1996 to 197.6.106 ind. in 2020. The catch of adults was closely related with the release of juveniles (r = 0.66) and increased from 800 t in 1996 to 18,968 t in 2019. Year-to-year dynamics of the chum salmon catch coincides in these two bays, i.e. strong year-classes provide good catch in both bays and low survival causes low catch everywhere. The spawners of age groups 2+ and 3+, mostly 3+ (62 %, on average) dominated in the catches in 2014–2022. This feature makes available the forecast of chum salmon landing in the Prostor and Kurilsky Bays because of strong dependence of annual catch of fish at the age 3+ on the catch at the age 2+ in preceding year (r = 0.89; rs = 0.98). Besides, a significant relationship is noted between the annual catches of chum and pink salmon belonged to the same year-class, i.e. between the catches of chum salmon at the age 3+ and the catches of pink salmon in preceding year (r = 0,71; rs = 0,75).
Spatial and bathymetric distribution and aggregation density is considered for bathyal crabs, including the grooved tanner crab <i>Chionoecetes tanneri</i>, on the data of specialized deep-water trap survey and two bottom trawl surveys within the depth range of 300‒1080 m conducted by TINRO in the northwestern Bering Sea in 2019–2020. The size of grooved tanner crab is determined as 9.0–17.0 cm for the morphometrically mature males and 6.5–15.5 cm for the morphometrically immature males, by carapace width. The size of 50 % morphometric maturity is evaluated for males of <i>Ch. Tanneri</i> in the northwestern Bering Sea. A new fishing measure is substantiated for this population taking into account its size composition.
Mortality rate of fur seal puppies is considered for the first two months of their postnatal ontogenesis, from the birth to leaving the rookery on Tyuleniy Island for wintering in the open waters of the Pacific. On average, 7.9 % of puppies die on the island, that is lower than the mortality on the rookeries on Commander Islands (14.4 %) and on Pribylov Islands (9.8 %). The higher mortality of puppies on Commander Islands is reasoned by their disease with uncinariosis at the northwestern rookery. In general, deaths of puppies have similar causes in different places of their birth: mainly exhaustion, injuries, and diseases.
Patterns of linear and weight growth of saffron cod in the first year of life are considered on the data of measurements and cited materials for different habitats of this species. The growth curve is approximated by logistic function. Monthly increments for the body length of larvae and fry are about 50–60 % in the first four months of life with the highest growth rate. Then the relative growth decreases significantly in fall-winter and does not exceed 1–4 % to the end of the first year of life. The absolute length increments increase during the first half of the year up to the maximum value of 25–30 mm/month in late summer – early autumn. Saffron cod grow faster in the southern areas of their habitat. The weight growth patterns are different from the linear growth. The weight growth is higher in the first five months of life, with gradual decreasing of the monthly weight increments form 156 % to 105 %. The relative weight increments exceed significantly the length increments in this period. When the body weight reaches app. 5 g, the relative weight increments decrease abruptly, though the absolute increments continue to increase until the 6–8th months of life when they reach 5–6 g per month for fish with body length > 86 mm. The body weight increases by 60 % in this short period of the highest weight growth. Time lag between the peaks of absolute linear growth (in July-September) and weight growth (in September-November) is about 2 months.
Seasonal and interannual variability of the demersal fish species composition is considered for the depths of 70–315 m in the eastern Kunashir Strait on the data obtained in 1998–2014. The fish community includes the species belonged to nine zoogeographical complexes and eighth ecological groups. Among them, species diversity is higher for the arctic-boreal, wide-boreal Pacific, wide-boreal Asian, and low-boreal Asian complexes and for the sublittoral, elittoral, and mesobental groups. The species diversity of fish in the surveyed area depends on seasonal migrations of demersal and pelagic fishes, including pacific salmon and some subtropical and tropical species. Interannual variations in the species composition are determined mainly by changes in the depth of netting and water temperature, but do not depend on the timing of samples collection during a season.
Current state of <i>Chlamys swiftii</i> settlements and resources of this species in the coastal waters of Primorye (Japan Sea) are considered on the base of surveys conducted in 2007–2021. The data on spatial distribution and abundance of the scallops were obtained by methods of scuba counts at the depth < 20 m. The total biomass and abundance were calculated using the Voronoi diagrams (Thiessen polygons). In total, the data were analyzed for 13457 stations located along the entire coast of Primorye from the Tumannaya/Tumen River mouth to Cape Zolotoy where 2875 scallops were sampled, weighted and measured. The average density of <i>Ch. Swiftii</i> abundance and biomass distribution was estimated. The scallops do not form dense settlements suitable for commercial fishery. The settlements with the highest mean biomass (22.5 ± 5.0 g/m2) were concentrated in the area from Cape Povorotny to Cape Yuzhny, and the lowest biomass of the settlements was observed in Peter the Great Bay (3.7 ± 2.1 g/m2). The settlements had mosaic distribution. The total stock of the species is estimated as 1.4 . 103 t, the commercial stock – as 1.3 . 103 t. About 99 % of the total stock was concentrated at the eastern coast of Primorye in the area from Cape Povorotny to Cape Zolotoy. More regular and mass recruitment is noted for the settlements in this area, than in Peter the Great Bay. Percentage of scallops with non-commercial size varied from 1.9 to 19.0 %, by years, whereas the scallops at the age 3–7 years with shell height 70–110 mm dominated in the area from Cape Povorotny to Cape Zolotoy and those at the age 3–6 years with shell height 80–115 mm – in Peter the Great Bay. The modal age of <i>Ch. Swiftii</i> was 4 years, the oldest specimens reached 7–12 years, by surveys.
Size-age structure and spatial distribution of pacific oyster <i>Crassostrea gigas</i> in the Busse Lagoon (Sakhalin Island) in 2010–2020 are analyzed. The oyster colony is in depression. Height of the shells, weight and age of clams have decreased significantly during the decade of observations. The oysters with non-commercial size dominate in the colony.
Results of biological analysis are presented for 162 specimens of coho salmon caught at the coast and in the rivers of Iturup Island (southern Kuril Islands) during their spawning migration in August-October, 2021. Almost all females and males close to puberty in the current year spent one year in the sea and were aged 1.1+ (66.7 %) and 2.1+ (30.0 %). The fish that spent two years in the sea were single – 1 specimen aged 1.2+ and 3 specimens aged 2.2+ (2.5 %). Taking into account the age of puberty and the body weight (2.63 kg for females and 2.44 kg for males, on average) the spawners reproduction in short streams is assumed. The high value of the gonad-somatic index (up to 20–22 % for some females) is other evidence that all these fish cannot run to other spawning areas but at least a part of them should spawn in the water bodies of Iturup Island. Indeed, some coho salmon were captured directly in the rivers. Beside the spawning fish, two actively feeding coho females aged 0.0+ (0.55 kg) and 1.0+ (1.11 kg) were caught with fixed nets.
ENVIRONMENTS OF FISHERIES RESOURCES
Functioning of a coastal seal rookery is considered on example of those located on Dolgiy Island in Lake Baikal, regularly visited by baikal seal <i>Pusa sibirica</i> Gm., which is constantly monitored by video surveillance. A case of the year 2020 with extremely early (comparing to 2011–2019) destruction and disappearance of ice in the northern part of the lake and rapid rise of the water level in summer-autumn is analyzed. Timing of the seals haul onshore and their abundance in rookery depend on the ice conditions: the lower ice cover – the earlier hauling-out and the higher abundance. Since the beginning of the rookery formation in May, up to 400 animals roosted there at the same time. Too early disappearance of the floating ice caused an abnormally large portion of individuals with incomplete molting on the rookery, and the delay in molting affected likely negatively on the animals health. Other negative factor was the deficit of available solid substrate for hauling-out because of rapid rise of the water level, particular in early summer. However, a large number of very well-fed adult females and males was observed on the rookery in May; presumably they did not participate in reproduction of population in 2020.
Data on feeding of walleye pollock <i>Gadus chalcogrammus</i> (3–70 cm long) in the Chukchi Sea in summer-autumn of 2017–2020 are presented. The food base includes zooplankton, benthic invertebrates and fish. The juveniles in the northwestern part of the sea consumed 0.033 t/km2 of prey per day, mainly fish (30.9 %), mysids (20.1 %) and amphipods (13.9 %), whereas the portion of copepods and euphausiids was 5.0–7.6 % of the diet. In the southwestern part of the sea, the juveniles consumption was much higher, as 0.200 t/km2 of prey per day, and included mainly euphausiids and copepods (24.9–51.1%). The adults with length 40–70 cm long dominated in the southwestern Chukchi Sea and consumed on average 13.2 t/km2 of prey per day, shared between fish (42 %), euphausiids (20 %), copepods (6 %), and decapods (11 %). Composition and structure of plankton was different between the main water masses on the shelf occupied the northern and the southern parts of the sea. In the northwestern Chukchi Sea, zooplankton distributed with the mean spatial density of 56.3 t/km2, formed mostly by chaetognaths (35.3 t/km2) and copepods (12.6 t/km2). In the southwestern Chukchi Sea, the mean spatial density of zooplankton was 49.2 t/km2, mostly euphausiids (17.3 t/km2), chaetognaths (15.8 t/km2) and copepods (9.2 t/km2). The total density was close to the level observed in the 2000s, but slight decreasing in biomass of chaetognaths and copepods was observed, mainly due to the recent lack of cold-water species <i>Calanus glacialis</i>, whereas the biomass of euphausiids, in particularly <i>Thysanoessa inermis</i>, had almost doubled. Biomass of the main groups of zooplankton prevailing in the diet in the Chukchi Sea in summer-autumn, as copepods and euphausiids, exceeded daily consumption of these groups by walleye pollock in 6–11 times that may indicate a sufficient food supply for this species. Besides, walleye pollock dwelled at the sea bottom and fed on shrimps, gammarids, bottom polychaetes, echiurids, mollusks, and also bottom fish. Total fullness of the pollock stomachs was in the range of 218–228 ‱ that also suggested successful feeding.
Database for the data of oceanographic observations in the eastern part of the Okhotsk Sea (on the shelf of West Kamchatka and in adjacent waters) obtained in 1888–2020 is created in KamchatNIRO (Petropavlovsk-Kamchatsky) that introduces many previously inaccessible data into scientific circulation and thus provides new possibilities for exploration of this area. The database is heterogeneous in its temporal and spatial resolution. The 1961–1990 period is better covered by the data, whereas the observations in the last three decades (1991–2020) are slightly less numerous. Spatial density of observations increases from the open sea to the coast and from the north to the south; the densest net of stations is located at the southwestern coast of Kamchatka.
Influence of heavy metals as zinc and iron with concentrations of 50 and 100 mg/L on dynamics of the cells abundance, morphology, fluorescence of chlorophyll a, and green autofluorescence is examined for the microalgae Prorocentrum foraminosum. The impact was measured on the 3rd and 7th days of the experiment. Both elements in concentration above the maximum permissible levels reduce the cells number, with the higher impact for Fe3+. However, Fe3+ caused no changes in structure of cells. The impact of Zn2+ caused the cells deformation and excretion of the cellular content. The chloroplast fluorescence became less intensive under influence of Fe3+, but the green autofluorescence had increased under presence of Zn2+ and Fe3+ in the medium.
PROMRYBOLOVSTVO
A technique for designing the rope-net shell of midwater trawl is described on example of the trawl Sirius Shelf project AS 11.012.000 designed by Aquaservice Ltd. Diagrams of the rope-net shell parameters distribution along trawl are used. The technique allows to analyze variations of these parameters for their optimization. A wide range of the trawl designing criteria can be taken into account using the diagram approach.
METHODS OF INVESTIGATIONS
The main part of the spawning grounds of herring in the northwestern Okhotsk Sea, from the Ayan Bay to the Eirineiskaya Bay, was surveyed on June 3–21, 2022 using standard methods of the roe diving survey. In order to rationalize the survey methodology, the herring population fertility (PF) was evaluated using two different approaches. The first is a standard method (described by Farkhutdinov, 2005) with calculation of the spawning ground areas and the roe density (RD) for each of them. The second method is based on the relationship between the total area of spawning grounds and PF detected previously by Dulenin and Didenko (2021). The spawning conditions for Okhotsk herring were abnormal in 2022. Just before the mass spawning, a strong storm had destroyed many spawning substrates and redistributed the spawning shoals of herring in the coastal zone. As the result, mean RD was extremely low – 1075318 eggs/m2 (long-term average value was 4170320 eggs/m2), but herring spawned in new areas, additionally to usual spawning grounds, so the total area of surveyed spawning grounds was rather large, as 38.68 km2. The population fertility calculated for this total area using the relationship between these indices was 182 . 1012 eggs that corresponded to the spawning stock number (SSN) of 6.513 . 109 ind. and the spawning stock biomass (SSB) of 1.823 . 106 t. These estimates match well with results of the stock assessment by other methods. On the contrary, unrealistic low assessments were provided using the routine method with calculation of RD on the annually surveyed spawning grounds (PF 51 . 1012 eggs, SSN 1.936 . 109 ind., SSB 0.542 . 106 t), because the spawning on destructed substrate could not represent adequately the state of the herring population during 2–3 years, until restoration of the algae belt. Besides, the standard method for data processing of the roe diving surveys is based on a number of non-formalized subjective assessments and assumptions that cannot ensure verification of the survey results. In opposite to this disadvantage, the calculation of PF by the area of spawning grounds is methodologically simple and allows to use remotely operated underwater vehicles, unmanned aerial vehicles and geographic information systems, with complete hardware and software documentation of survey materials. Thus, the PF evaluation using its relationship with the total area of spawning grounds is recommended for introduction as the main method of the Okhotsk herring stock assessment.
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