Summer sandeel consumption by seabirds breeding in the Firth of Forth, south-east Scotland

The industrial fishery for lesser sandeels (Ammodytes marinus) is currently the largest single-species fishery in the North Sea and this species is also the main food of many seabirds breeding in colonies in this area. It has been suggested that inshore sandeel fisheries could have adverse consequences for local seabird populations. One potential area of concern is the fishing grounds on the banks (Wee Bankie and Marr Bank) which lie approximately 40 km off the coast of south-east Scotland, well within the feeding range of many seabirds breeding at colonies in and around the Firth of Forth. A bioenergetics model is used to estimate that seabirds associated with these colonies consumed 6000-17000 t of sandeels during each of the summers of 1996 and 1997, with the majority of the fish being in the 1-group or older age categories. Distributions of birds at sea recorded during a systematic survey during the breeding season demonstrated that the Wee Bankie was an important feeding area for guillemot (Uria aalge), razorbill (Alca torda), and kittiwake (Rissa tridactyla) and to a lesser extent puffin (Fratercula arctica) indicating that the exploitation of sandeels by these species shows strong spatial overlap with the industrial fishery. In contrast, shags (Phalacrocorax aristotelis) and common/arctic terns (Sterna hirundo/paradisaea) showed predominantly inshore distributions while the North Atlantic gannet (Morus bassanus) probably fed mainly outside the area surveyed. Species-specific comparisons of the estimated size of the observed at-sea populations with those predicted from the number of individuals associated with colonies in the area suggests that during the chick-rearing period a high proportion of the Firth of Forth guillemot population was feeding in the surveyed area. However, for the other species the number observed at sea was consistently lower than predicted. The size of the sandeel stock associated with the Wee Bankie is currently unknown. Comparison of the size of the annual catch of the fishery and the amount taken by seabirds indicates that in most years the former has been consistently higher than the latter. Thus the potential for the fishery to affect seabirds is likely to be greater than the converse. (C) 1998 International Council for the Exploration of the Sea.