Different organochlorine contaminant profiles in groups of flounders (Platichthys flesus) from sampling locations around Denmark

Flounders (Platichthys flesus) from the waters around Denmark were analysed for their organochlorine (OC) profile to study whether fish from the same genetic population could be separated into characteristic subpopulations, based on their feeding grounds. The chemical analysis of fish liver provided a data set of 16 OC compounds in 94 samples from 2004 to 2006. Except for hexachlorocyclohexane, OC compounds were intercorrelated, indicating similar environmental fate and bioaccumulation. OC profiles are less affected than absolute concentrations by potentially confounding biological factors and thus more suitable for studies of intrapopulation differences in relation to feeding grounds. Principal component analysis grouped the samples according to locations. All but three of the 94 samples could be reclassified. Samples from the same and additional locations collected in 2003 provided validation, with only few misclassifications. This statistical separation likely reflects location-specific pollutant patterns in sediments and biota, even on the relatively small scale of this study. Thus, despite the lack of genetic differences, characteristic subpopulations of flounders could be identified with separate feeding grounds. OC profiles have been used increasingly to distinguish stocks.