J. Horppila et H. Peltonen, THE FATE OF A ROACH RUTILUS-RUTILUS STOCK UNDER AN EXTREMELY STRONG FISHING PRESSURE AND ITS PREDICTED DEVELOPMENT AFTER THE CESSATION OF MASS REMOVAL, Journal of Fish Biology, 45(5), 1994, pp. 777-786
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.