Stock trends in six North Sea stocks as revealed by an analysis of research vessel surveys

A model is developed for the analysis of age disaggregated indices of abundance from which stock trends can be estimated. The model is used to examine trends in North Sea cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), sole (Solea solea), plaice (Pleuronectes platessa) and herring (Clupea harengus). These are compared with the trends estimated from conventional ICES assessments which use commercial catch-at-age data. The catch data are known to be affected by misreporting which can affect the calculated stock trends. The surveys appear to be able to quantify the trends in recruitment and spawning stock with a high degree of consistency between independent surveys of the same stock and with the conventional assessment. Estimates of catch and fishing mortality rate are more uncertain. The well known problems of catch mis-reporting which affect the conventional ICES assessments do not appear large enough to alter the perception of stock trends