Stock'related changes in biological parameters of the Icelandic summer'Spawning herring

During the period 1960–1992 the stock size of Icelandic summer-spawning herring varied from about 300 000 t in the early 1960s to just above 10000 t in the early 1970s. Since then the stock size has increased to about 400 000 t in 1992. Examination of the mean weight at age and length at age as well as condition factor of the herring revealed that these parameters have fluctuated slightly, but without a trend, over a wide range of stock abundance, but increased when the stock was at extremely low level of stock abundance. Examination of the stock-recruitment relationship revealed that there were clear positive signs of increased recruitment at high stock levels. Similarly there were signs that the recruitment level was greatly affected by the cold period 1964–1971. Comparison of the VPA stock estimates and acoustic stock estimates indicated that the natural mortality is in the range of 0.1-0.15.