THE FATE OF A ROACH RUTILUS-RUTILUS STOCK UNDER AN EXTREMELY STRONG FISHING PRESSURE AND ITS PREDICTED DEVELOPMENT AFTER THE CESSATION OF MASS REMOVAL

The effects of very intensive exploitation on a roach stock over 5 years are estimated. The total roach catch of the mass removal carried out with trawls was 507 metric tons (195 kg ha-1, 54% of the total catch). According to the virtual population analysis the biomass of the stock has decreased from 180 kg ha-1 in 1989 to c. 50 kg ha-1 in 1993. The production of the stock has fallen from 64 to 33 kg ha-1. The stock is dominated by younger age groups than before the mass removal. The future development of the stock is predicted by considering different levels of natural and fishing mortality. If the exploitation is stopped totally after 1993, roach biomass is predicted to double in 3 years. A constant fishing mortality rate of 0.3 (yearly catches 45-50 metric tons) would prevent the recovery of the stock, providing that 1-year-old and older roaches are exploited.