Abestract
This study aimed to evaluate the quantitative (number of fish, catch figures and caviar harvest) and qualitative changes (sex composition, age and length) of sturgeons, as well as to calculate their catch per unit effort (CPUE), and investigate catch trends and spatial and temporal distribution of sturgeon in 2016 through 2018.Changes in sturgeon stocks in the Iranian coastal waters of the Caspian Sea were analyzed using different population parameters including catch figures, CPUE, length, age, weight, sex composition and weight of caviar. The biometry data of all sturgeon caught were collected from all catch stations of the Northern provinces. CPUE in catch stations (which uses gill nets for sturgeon catch) was estimated in terms of per fishing boats×days×100 gill nets and in seine fishing based on the number of sturgeon caught per one seine operation. Fishing statistics including the number of sturgeon caught the amount of catch show a decrease in the amount of catch during the years 2016 to 2018. In the fishing stations of all three provinces, the number and weight of catch in the studied years decreased but the number and weight of catch in seine fishing of all three provinces increased. Persian sturgeon with 70.9-74.8% was dominant and followed by stellate sturgeon with about 20%.In terms of weight, Persian sturgeon has the highest weight contribution of the catch and Beluga was in the second place. The amount of caviar caught in fishing stations decreased by 58.4% and increased by 169% in seine fishing cooperatives. In 2016-2018, between 65 and 55% of the total caviar was supplied by Persian sturgeon.The amount of catch per unit effort of total sturgeon fish in sturgeon fishing stations in 2018 compared to 2016 decreased by 48.7% but this figure increased by 5.4% in seine fishing cooperatives. The highest number of catches per unit effort was in Golestan province in both fishing stations and seine fishing cooperatives in all these three years.Beluga sturgeon has the highest CPUE only in Golestan province and this figure for Persian sturgeon was in Golestan and Mazandaran provinces and for stellate sturgeon was in the central regions (Mazandaran province) and Guilan province. The average length of stellate sturgeon has increased but has little changes in Persian sturgeon.Males were the predominant sex in Persian sturgeon species. In 2016, females of beluga sturgeon were the predominant sex and in 2018, males of this species had the highest share of total catch. This change was due to the increase in the share of females of beluga sturgeon in the seine fishing cooperatives. Females of the stellate sturgeon were also the dominant species of the catch. The highest quality of caviar of all sturgeon species was grade one, but in October, the percentage of caviar of grade two was higher than other grades in seine fishing cooperatives and in fishing stations. The average weight of fish caught in sturgeon gill nets was much higher than the seine fishing cooperatives. The percentage of caviar weight to gravid females’ body weight in stellate sturgeon was 18.3%, Persian sturgeon was 18.6% and beluga was 12.9%.Due to the sharp decline in natural and artificial breeding of sturgeon in recent years and the lack of proper protection and conservation of sturgeon stocks, especially juvenile sturgeon, it seems that the population of these fish will continue to decline sharply in the coming years and reach a minimum stock over the next ten years. Implementation of a comprehensive plan to conserve sturgeon resources in order to reduce illegal fishing and pouching pay more attention to providing conditions for natural reproduction and artificial propagation and release of juveniles and comprehensive executive and research cooperation of the Caspian littoral states are the most important activities in restoring and preserving the unique and valuable sturgeon stocks.
Keywords: Age , Caspian Sea, CPUE, Length, Sturgeon