One of the biggest problems faced by fisheries management is the issue of bycatch and discards. The target species of fisheries are often found in association with other organisms. Despite attempts to reduce bycatch through technical modifications, the indiscriminate nature of many fishing gears means that nontarget species become incidental catch or bycatch. This study assessed the spatial variation across four fishing grounds in the composition of bycatch of an otter trawl scallop (Aequipecten opercularis) fishery in the Irish Sea. The results showed that the percentage of bycatch in the fishery as a whole was relatively low at 7.42 ± 0.52 by weight of the total catch. In 2012, the total bycatch for the fishery was estimated to be 309 tonnes compared to landings of queen scallops of 2,410 tonnes, landed by Manx trawlers either to the Isle of Man or United Kingdom. Significant differences were found between the four fishing grounds in relation to mean catch by weight, mean bycatch by weight, and bycatch species composition; however, there was no significant difference found in diversity and species abundance among the four fishing grounds. The results demonstrated that fishing ground was the dominant factor controlling bycatch variation within this fishery, which was related to some extent to water depth. The findings of the study indicate that understanding variation in bycatch in relation to the characteristics of different fishing grounds would enable fishermen and managers to manage (minimize) bycatch through the use of temporary spatial management measures.