О запасах кильки и их использовании в северной и восточной Балтике.
This paper deals with the results of investigations on the condition and exploitation of sprat stocks in the northern and eastern areas of the Baltic during the period from 1957 to 1974. The age structure of the Baltic sprat stocks surveys can best be determined by means of overwintering concentrations in which all age groups are concentrated except the one year old sprats which remain at depths of 40 to 50 m in winter. The relative abundances of the individual year classes was determined by the per-cent composition of catches. The relative strength of the sprat stocks (in indices) in the northern areas of the Baltic was determined for the period from 1960 to 1974 on the basis of the relative numbers of the year classes, the mean percentile part of the age groups in the catches (which show the mortality) and the mean weight of the fish in the age groups (maximum of occurrence — in the season 1960—61, minimum of occurrence in the period 1967—68). These indices were also used for the prediction of state and age structure of the sprat stocks for 1975 and 1976. The mortality of the sprat was insignificant in the northern areas during the period from 1960 to 1974 (total mortality 0,3 to 0,4; natural mortality 0,1). This fact can be explained, by the occurrence of a succession of productive year classes (1955, 1957 and 1959) and by a reduction in the cod abundance in these areas due to unfavourable hydrological conditions. The intensity of the exploitation of sprats has increased continually during the last decade and has reached its optimum or even the maximum in the northern and eastern areas of the Baltic as shown in the catch graphs (Beverton. 1973). Therefore it is necessary to regulate the exploitation of sprats in the whole area of the Baltic (limitation of the fishing intensity, introduction of minimum sizes for sprat).
| Main Authors: | , |
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| Format: | Journal Contribution biblioteca |
| Language: | Russian |
| Published: |
1975
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| Subjects: | Baltic sprat, Exploitation of sprat stock, Prediction of state of sprat stocks, ASFA_2015::F::Fish stocks, ASFA_2015::A::Age composition, ASFA_2015::P::Population abundance (in number), |
| Online Access: | http://hdl.handle.net/1834/15878 |
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