Distribution and damage to the by-catch assemblages of the northern Irish Sea scallop dredge fisheries

The major by-catch species retained during twice yearly dredge surveys of g reat scallop, Peten maximus, and queen scallop, Aequipecten opercularis, (b oth Mollusca: Pectinidae) populations on 13 fishing grounds in the northern Irish Sea, over a period of five years, were identified and enumerated. Ad ditionally, the damage sustained by the by-catch was assessed and related t o a range of physical parameters recorded during the survey. A number of sp ecies captured in the spring-toothed dredges exhibited differences in abund ance and damage sustained between years, and also between the, start and en d of the closed season for great scallop fishing (1 June-31 October). The b y-catch assemblage varied geographically dependent upon the underlying comm unity structure, as well as putative factors including gear efficiency and substratum type. Two clear assemblage types were identified by multivariate analysis, one to the southwest of the Isle of Man, the other covering fish ing grounds to the north, east and south of the island. There is a hierarch y of species sensitivity to damage in great and queen scallop dredges, prob ably related to morphological and behavioural characteristics. This selecti ve mortality of a fraction of the community may have long-term implications at the ecosystem level. The degree of damage sustained by many species is related to both the volume of stones retained in the dredge, and the total volume of the catch (dredge fullness. If these were reduced, the overall ma gnitude of incidental by-catch mortality would be lower.