Vol 59, No 4 (2019)

Based on the materials of the trawl survey conducted at depths of 81–301 m in the northwestern part of the Sea of ​​Okhotsk in August–September 2013, the species composition and characteristics of bottom shelf fish’s distribution are described. On the shelf, 69 species were recorded, including 54 species from 11 families, among which Zoarcidae (19 species), Liparidae (17), Cottidae (7), Pleuronectidae (7), and Cyclopteridae (5) dominate in terms of the number of species and abundance. Two groups of fish were identified on the shelf: one is made up of species that prefer extremely low temperatures of the western Sea of Okhotsk cold lens (below –1°C), and some of them are found only within it’s range; the other includes the species that avoid it. The boundary between shelf and bathyal ichthyocenes passes through an isobath of 200 m. Depths of 150–250 m are populated by an ecotone community, in which a sharp transition from shelf to bathyal ichthyocene is observed.

A bottom trawl survey was conducted in August and September 2018 at the outer edge of the continental shelf and the upper part of the Pacific slope of the northern Kuril Islands and southeastern Kamchatka, between 48° and 52° N, at depths of 100–1000 m. Biomass and abundance of all caught fish species were calculated using the obtained data. A total of 121 species were recorded, including 98 demersal and 23 pelagic and anadromous fishes; their total stock amounted to 406 000 t. The stock estimates of the common fish species were compared with the values inferred from analogous surveys in summer 1989 and spring 2009; a comparison of the bathymetric distribution of species between 2018 and 2009 was also carried out.

In the system of lakes Bol’shoe Leprindo and Maloe Leprindo (Lena basin, Transbaikalia), spawning of two isolated populations of the dwarf form of Arctic charr Salvelinus alpinus was studied. The results supplemented with the data about the exterminated large form from these lakes, demonstrate a unique combination of sympatric and parapatric charr forms with autumn (large form), summer (dwarf form, Bol’shoe Leprindo) and first recorded in Russia winter-spring (dwarf form, Maloe Leprindo) spawning peaks. In both lakes, the dwarf form spawns in the profundal zone at silty bottom at the depth 25–58 m: in Bol’shoe Leprindo, from late June to October with peak in July-August when water temperature is 5–6°С, in Maloe Leprindo from January to July, with peak in January–March when temperature is 2.5–3.0°С. Eggs laid in July–August in Bol’shoe Leprindo develop for 3.0–3.5 months, eggs laid in January–March in Maloe Leprindo, for about 4.0–4.5 month; in both lakes they are actively consumed by burbot Lota lota. Due to smaller egg size the dwarf form has twice as high individual relative fecundity as the large form, which compensates for high egg mortality. It is supposed that the differences in spawning strategies were formed as the result of outcompeting of the dwarf form by the large form from the littoral to the profundal zone, where perennial low temperature favoured the prolongation and displacement of their spawning time. These differences determined reproductive isolation and genetic divergence between three charr populations.

Six groups have been identified in the species' population structure based on the analysis of microsatellite markers' polymorphism in Pacific cod Gadus macrocephalus samples within the entire western part of the North Pacific, including waters of the Pacific coast of Canada. The first group includes cod from waters of the Yellow Sea; the second group consists of cod from the Sea of Japan (eastern coast of Korea and Peter the Great Bay); the third group combines cod from Tatar Strait and the South Kuril Islands (both Sea of Okhotsk and Pacific Ocean sides); the fourth group is formed by cod from the northwestern Sea of Okhotsk and Taui Bay; the fifth-largest group includes cod from waters off western Kamchatka, the North Kuril Islands (Sea of Okhotsk and Pacific Ocean sides), Karaginsky Bay, Navarinsky area in the Bering Sea, and Anadyr Bay; the sixth group is formed by cod from coastal waters of Canada.

The age and growth of Mullus barbatus L. 1758, sampled around the Gökçeada Island from September 2014 to June 2015 was determined. A lifetime of 0–VII years was found using age derived from otolith readings. A total of 717 specimen ranging from 70 to 227 mm TL were collected. The length-weight relationship of the species was W = 0.006L^3.22 for all individuals. The estimated von Bertalanffy growth parameters were L_∞ = 27.2 cm, k = 0.17 yr^–1, t₀ = –2.49 for females, and L_∞ = 15.9 cm, k = 0.74 yr^–1, t₀ = –0.83 for males.

Based on materials from bottom trawl surveys of 2009–2015, biomass and abundance of bottom fish of the Sea of ​​Japan between the Povorotny and Zolotoy capes (Northern Primorye) were estimated. Information is provided on the population structure of common fish species in the study area. According to the long-term biomass data, scale-eye plaice Acanthopsetta nadeshnyi (20.43%) and Alaska pollock Gadus chalcogrammus (11.31%) dominate. The total average annual ichthyomass is 188 300 t or 5.4 t/km²; the number is 1482.6 million ind. or 42 300 ind./km². The average specific biomass of fish varied over the years from 1.8 (in 2010) to 7.8 t/km² (in 2014). In 2010, compared to 2000, the average specific biomass of fish has increased approximately twofold due to the appearance of a number of generations of common species of the bottom ichthyocene relative to the productive generations.

Palatability of sodium cholate (10^–1 M), sodium taurocholate (10^–1 M), and dehydrocholic acid (0.5 × 10^–3 M) for Mexican cavefish Astyanax fasciatus (blind form), silver dollar Metynnis argenteus, Nile tilapia Oreochromis niloticus, green swordtail Xiphophorus hellerii, and roach Rutilus rutilus was assessed. All substances have a significant taste effect, but the reaction of fishes to their taste is different and the responses to the same substance were different. Taste attractiveness for bile substances (sodium taurocholate, dehydrocholic acid) was found only in Mexican cavefish, which allows it to feed on specific food (bat guano) available in cave reservoirs where other food resources are extremely insignificant. For the rest of the fishes, bile substances had an inert or aversive taste, which can prevent coprophagy and contribute to long-term preservation of feces in the environment, which are an important source of odor signals for fish. It has been proposed to consider bile substances as important chemical regulators of fish relationships in aquatic communities.

Visual observation data of the Greenland shark Somniosus microcephalus in August–September 2017 in the Kara Sea specifying the species range in this Arctic region are presented. Six cases of species registration in the surface waters were recorded. The factors limiting the distribution of sharks on the Arctic shelf are discussed.