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 yea rs are estimated. The total roach catch of the mass removal carried ou t 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 sto ck has decreased from 180 kg ha-1 in 1989 to c. 50 kg ha-1 in 1993. Th e 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 f uture development of the stock is predicted by considering different l evels 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-o ld and older roaches are exploited.