Assessments of the lesser sandeel ( Ammodytes marinus) in the North Sea based on revised stock divisions

Abstract

Recent investigations suggest that the current treatment of North Sea sandeel ( Ammodytes marinus) as a single unit stock may have little biological basis. In order to study regional effects of the fishery on North Sea lesser sandeel it may therefore be important to assess stock dynamics for the different aggregations. Based on a geographical division of the North Sea in a number of proposed assessment regions, regional as well as whole North Sea sandeel assessments are presented based on revised data (e.g. catch in numbers at age and effort). The assessments suggest regional differences in fishing effort, catch per unit effort, yield, fishing and natural mortality. A better understanding of sandeel growth is important for stock and catch predictions because previous studies indicate that the variability of mean weight-at-age is one of the most important factors influencing the precision of predictions. The Danish weight-at-age data of sandeel are re-analysed to estimate the mean weight-at-age in the catch and the stock and the precision of the estimates. The reliability of the sandeel assessments is discussed in relation to the data sources available and to the knowledge of sandeel biology and population structure in the North Sea.