An investigation of the Irish ray fishery in ICES Divisions VIIa and VIIg

Abstract

A study of the mixed-species ray fishery off the east and southeast coast of Ireland was carried out between 1997 and 1998, which involved port sampling and collection of commercial transactions data and official logbook data. Several years of commercial transactions data collected allowed seasonal trends in the relative abundance of the commercial size grades to be deciphered. Catch composition by species and sex was determined for the entire ray landings of individual vessels in the fishery during each port sampling occasion. Biological data were collected from 17 450 rays during 1997 and these data were used to reconstruct the size and age structure of the population at the species level. Each species had a narrow age distribution, generally ranging from 2 to 8 years. Total mortality estimates (Z1) derived from catch curves were high, ranging from 0.456 for female Raja brachyura to 1.110 for male Raja montagui, but were generally lower than the total instantaneous mortality derived, with the exception of male R. montagui (Z1=0.813). Demographic analysis, using life tables, revealed that, with the exception R. montagui (r=-0.045), each of the commercial species had positive population growth, ranging from r=0.125 for R. clavata to r=0.224 for R. brachyura. The results of the analyses are discussed with respect to previous studies and observed trends in the fishery.