Growth of sandeel, Ammodytes marinus, in the northern North Sea and Norwegian coastal waters

The somatic growth of lesser sandeel, Ammodytes marinus, was highly seasonal with the strongest growth in weight and length occurring in the period March–June. The condition factor also showed a pronounced seasonal pattern. In the latter half of the year, the observed mean length-at-age declined. Mean length and weight of the 0-group increased from first appearance in near-bottom catches in June until at least October. Sandeel on fishing grounds of the northern North Sea usually had greater sizes-at-age than sandeels on an unexploited coastal bank off southwestern Norway. In the North Sea, mean length, weight, and condition-at-age differed between year-classes. The abundant 1996 year-class had comparatively low length, weight, and condition-at-age, i.e. not different from that of the coastal sandeel. Comparisons of new and historical growth data from the North Sea showed that both spatial and temporal variation in growth could be substantial. No evidence for growth compensation due to enhanced mortality from commercial exploitation was found but sandeel on the main fishing areas of the northern North Sea and the southwestern Dogger Bank may grow faster than those in coastal waters. We hypothesise that temporal and spatial variation in food availability within the North Sea is important for modulating the growth of sandeel. The reduced mean size-at-age for the 1996 year-class suggests that density-dependent processes may affect growth of exceptionally abundant year-classes.