Trends in stocks fluctuation of Rutilus frisii kutum in the Caspian Sea

Abstract

Overfishing, destniction of spawning grounds together with intensive artificial reproduction and release of Rutilus fish/ kutum fingerlings have caused remarkable fluctuations in the stocks of the fish in the Caspian Sea over the past decades. The mean catch size of the fish during periods 1937-1947, 1967-1977 and 1987-1997 were 3110, 990 and 8505 tons respectively. Also the minimum catch was recorded as 121 tons in 1964 and the maximum catch was recorded as 11175 tons in 1994. The catch per unit effort (CPUE) of the species shows high variations such that it has been 17 kg/ton in 1971, 216 kg/ton in 1989 and 112 kg/ton in 1999. The decline in CPUE in 1999 was due to increased fishing efforts of 3.8 orders of magnitude (in comparison to the year 1989) as a result of fishing cooperatives increasing in number during that period. The calculated stock biomass of the fish was 1300 tons in 1971 fluctuating between 18489 to 25400 tons in the period 1990-2000. The mean biomass of the fish in the recent past 10 years was 22750 tons which shows 17-fold increase in comparison to the year 1971. The accomplished catch in the recent 10 years has been 35 to 46 % of the annual stock. The exploitation rate being more than MSY and decreased mean weight of the released fingerlings plus lowered return rate might have caused the decrease in the stock size of the fish during 1998-1999.