This research was funded by Defra projects SF0250 and SF0246 to CNT. Cefas provided help, advice and samples from the North East Coast Driftnet Archive, with particular thanks to Barry Bendall and William Riley, and to CEH for help and samples from the River Frome Archive. Thanks also to Catherine Cole for help with sample preparation, to Mike Bolshaw for mass-spectrometry assistance and to Mark Moore and Elizabeth Kent for advice, all of the University of Southampton.