FISHING AND QUALITATIVE CHARACTERISTICS OF BIG-EYED SHAD ALOSA SAPOSCHNIKOWII (GRIMM) IN THE CASPIAN SEA
Journal Title: Вестник Астраханского государственного технического университета. Серия: Рыбное хозяйство - Year 2013, Vol 0, Issue 2
Abstract
The analysis of the current state of commercial catches of big-eyed shad stocks in the Caspian Sea, which is the backup target species, is carried out. The reasons for the variations in catch and biological parameters in long-term perspective are analyzed. The reduction of catches of herring in the Terek-Caspian region is conditioned by a complex of climatic phenomena (fluctuation of the Caspian Sea level), human factors and organizational and technical reasons. There is a clear downward trend in the rate of linear-weight growth in the same age groups. One of the factors that influences the growth rate and stocks of big-eye shad is its nutrition supply. After the disappearance of shellfish from the adult herring nutrition, the basis of food in the current conditions is fish forage (sardines, silversides, gobies). Almost year-round spawning of anchovy sprat provided with fodder juvenile and adult herring in the South Caspian. After the death of the two types of sprat the forage shortage has caused a gradual decline in the rate of linear-weight growth of herring, including big-eyed shad. By comparison of the previous data obtained during the rise of the sea level 1980–1995, with new materials in recent years, the negative trends occurring in the big-eyed shad population have been revealed, such as increase of the rate of natural mortality. The specifics of breeding and fish-growing period of big-eyed shad in the North Caspian for 5 months allowed gathering reliable data to estimate the number of both new generations and the total stock. The complete calculation of abundance, biomass and size of the fishing stock of 13 generations of big-eyed shad (from 2000 to 2012) is proposed. It is shown that stocks of big-eyed shad in the recent period are at a high level and in a stable condition, but since 2009 there has been a tendency to reduce them. The unusual situation of the recent years is that the decline in stock biomass occurred at high abundance of her-ring. The reason for such an inadequate reduction of biomass is a significant reduction in individual fish weight.
Authors and Affiliations
Svetlana Andrianova, Vitaliy Barabanov
Keywords
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