The role of thermal stratification on the population dynamics of Sagitta elegans Verrill in the western Irish Sea

Temperature and prey availability have a marked effect on thedevelopment and growth of Sagitta elegans. This study addressesthe effects of thermal stratification on the growth and sizeof adult S.elegans in the western Irish Sea. It shows that instratified waters, bottom water temperature had a greater effecton the development of mature adults than surface water temperature.Whilst the length of mature individuals caught in 1992 and 1994decreased with increasing temperature, they did not conformto the models of McLaren (1963) and Sameoto (1971), as the animalswere larger than predicted. The long breeding period found inthe stratified region, suggests that previous reports of oneor two generations per year in the western Irish Sea do notaccount for the likely mix of generations that occur from Februarythrough to September.