Monitoring the abundance and distribution of taxa is essential to assess their contribution to ecosystem
processes. For marine taxa that are difficult to study or have long been perceived of little ecological
importance, quantitative information is often lacking. This is the case for jellyfish (medusae and other
gelatinous plankton). In the present work, 4 years of scyphomedusae by-catch data from the 2007e2010
Irish Sea juvenile gadoid fish survey were analysed with three main objectives: (1) to provide quantitative
and spatially-explicit species-specific biomass data, for a region known to have an increasing trend
in jellyfish abundance;