Assessment of herring stocks south of 62°N

1.1 A description is given of the changes in the state of the North Sea

herring stocks since the second World War in terms of total catch,

stock size, fishing mortality, spawning potential and recruitment. It

is concluded that the high fishing intensity exerted on the stock

during the last decade has reduced the spawning potential at a rate

of about 20% per year. The decrease in biomass has led to a decline

in the total North Sea herring catch which at present is based upon

a few young year classes.

1.2 Based on the assumption that future year classes will be of average

strength, a prognosis of future catch and biomass is given for

different combinations of fishing mortalities for juvenile and adult

herring. Total allowable catch levels are deduced from this prognosis.

1.3 The existence of a stock/recruitment relationship for the total North Sea

stock has not yet been demonstrated.The possibility that such a

relation ·could arise by further reduction of the spawning potential

is pointed out. This could lead to a rapid collapse of the stocks