Preliminary results of fisheries research in the Laptev Sea at RV «Professor Levanidov» in September 2019

In September 2019, the R/V “Professor Levanidov” carried out comprehensive studies in the Laptev Sea from 140 ° to 110 ° E at depth range of 60–950 m. High positive anomalies of air and surface water temperatures were noted up to + 2 + 3 °C and +1.5 °C respectively with an abnormally low sea ice cover. Cold Arctic and desalinated waters of the river flow dominated in the upper 200 m layer. Atlantic waters were traced in the layer from 180–300 m to the bottom, and their core — at a maximum temperature of + 1.6 + 1.92 °C at 240–280 m. By the time of the survey, the active vegetation of phytoplankton had finished. Oxygen saturation in the almost the entire surface layer was below 100 %. Primary production was limited by mineral nitrogen concentration. Low concentrations of phosphates, nitrates and silicates in the intermediate waters indicated the penetration of Atlantic waters. The average biomass of plankton on the shelf was 239,8 mg/m 3 , on the slope — 374,2 mg/m 3 . Copepods and chaetognaths with considerable contribution of hyperiids and euphausiids dominated in plankton by weight. The bulk of zooplankton was large organisms, while small and medium fractions were 22 and 10 %. Brittle star, starfish, and shrimp dominated in trawl benthos. 25 demersal fish species of 14 families were found in bottom trawl catches. Zoarcidae, Liparidae and Gadidae were the most diverse. Polar cod was recorded along the entire route with highest concentrations in Atlantic waters at depths of 217–460 m. Copepods dominated in the diet of Polar cod juveniles, while that of adults was supplemented by large pelagic crustaceans and fish with high level of cannibalism. Greenland halibut was found along the entire continental slope at 270–750 m while the largest catches were in its central and western parts. The increase of halibut number and occurrence was due to the wide distribution of Atlantic waters on the slope. The main component of its diet was Polar cod