Estimating year-class strength of Icelandic summer-spawning herring on the basis of two survey methods

Recruitment indices at age 1 and 2 were constructed for Icelandic summer-spawning herring using data from two inherently different survey methods on their nursery areas for the years 1988-2003. The surveys were a shrimp, bottom-trawl survey and a herring acoustic survey. Indices were compared with the year-class strength at age 2 derived from an assessment model (AMCI) used for the stock. A juvenile index at age 1 from the acoustic survey and at age 2 from the shrimp-trawl survey correlated significantly with the modelled recruitment, although only marginally with each other. One index was not considered markedly better than the other, and both have shortcomings even if the acoustic survey is believed better than the trawl survey for quantifying juvenile herring. The recruitment index at age 1 derived from the acoustic survey can be improved as an indicator of recruitment if that survey were to be extended to cover the nursery areas off western and southeastern Iceland, and the same areas covered each year.