The data on the size, weight, age and sex composition of sprat Sprattus sprattus in the north-western Black Sea section were obtained on the basis of material collected in commercial vessels during 2007-2021. Totally 27,951 specimens were examined. It was revealed that over the past 50 years the sprat population has undergone significant structural changes. The large specimens' portion in population decreased as compared to 1970s and 1980s. The average individual size in the catches of midwater trawls decreased by 15-20. Compared to 1975, the asymptotic length of sprat, calculated using the Bertalanffy equation, decreased from 13.92 to 11.19 cm. The weight parameters of the species also decreased. The decline in the growth rate was caused by food competition with ctenophore Mnemiopsis leidyi. The ratios of natural and fishing mortality rates (F/M) and biomass at the actual level and at the level of maximum sustainable yield (B/BMSY) calculated using the LBB model were equal to 0.63 and 1.6 respectively. The ratio of the actual biomass to the biomass that sprat population could reach in the absence of fishing (B/B0) was 0.58. This indicates that the sprat stock is exploited at the level below the optimum and actual fishing intensity is not threatening. However, over the past two decades the biomass of commercial aggregations and catches in this sea section decreased tenfold. The depression of the stock has led to decrease of the fixed nets and trawl vessels number in fishing companies. The poor state of the sprat stock is caused by the negative environmental changes in the northwestern part of the Black Sea owing to anthropogenic impact in recent years. Restrictions on commercial fishing will not improve the state of sprat population.
Hulak et al. (Thu,) studied this question.