Current methods of subsea production systems survey in the conditions of the Arctic region

The development of deposits in the Arctic region and the Far Eastern shelf of Russia is complicated by the presence of ice conditions. The duration of the ice period can vary from 5 up to 9 months, during which the underwater equipment of the field is inaccessible for inspection and repair. This work discusses the methods of inspection and maintenance of subsea production systems that can be used in the development of Arctic deposits.

Current State and Economic Value of Astacofauna in Certain Areas of the Eastern Shelf of the Caspian Sea

Aim. The purpose of this work was to assess the current state of crayfish populations in their habitats on the eastern shelf of the Caspian Sea (Alexander Bekovich‐Cherkassky Bay).Material and Methods. Fieldwork was based on underwater research methods using light diving equipment. Collection of research material was carried out according to an established crayfish survey protocol using fixed grid sites of 100 square metres. Collected crayfish were identified by species, measured and weighed, fecundity of females and the condition of crayfish shells were recorded. Crayfish were then released back into the sea. Calculation of numbers was carried out on the basis of determination of cluster density (ind/m2) with a further assessment of useful biotype areas. Calculation of commercial stocks based on crayfish length. The research synthesized information derived from comparative analysis of modern research results and archival data from the 1970s to 1990s.Results. Analysis showed that significant changes in the composition of populations had occurred. The dominant species recorded was Caspiastacus pachypus Rathke which has substantially displaced from the biotopes Pontastacus eichwald Воtt. which was previously the dominant species here.Conclusion. Comparative analysis of the modern state of the astacofauna on the eastern shelf and historical data indicates significant changes in the structure of populations of Caspian crayfish. The resilient C. pachypus has become the dominant species. Its small commercial size has significantly reduced the economic value of crayfish stocks. In general, however, commercial stocks of these crayfish make it possible to develop these marine biological resources.