• marine mammals;
  • cetaceans;
  • pinnipeds;
  • pollutants;
  • organochlorines;
  • techniques;
  • population discreteness;
  • distribution;
  • stock identity


Organochlorine pollutants are potentially useful for identifying discrete populations of marine mammals that overlap in geographic distribution. However, many factors unrelated to geographical distribution may affect the chemical burden of individual animals or of entire population components even within a homogeneously distributed population. These factors include. among others, nutritional state, sex, age, trophic level, distance of habitat from mainland and pollution source, excretion. metabolism, and tissue composition. Sample storage and analytical methodology may also be an important source of variation. These, and any other factors, must be identified and their effect ascertained before attempting any comparison between populations. This paper critically examines the nature and magnitude of the effects of these factors on organochlorine tissue loads in marine mammals. Pollutant concentrations can be strongly biased if carefully designed sampling regimes are not followed, but they are affected only moderately by sample treatment after collection. Conversely, ratios between concentrations of compounds, such as the DDE/tDDT or the tDDT/PCB ratios, seem less dependent on sampling regime but more affected by storage. analytical procedures and ecological variations such as distance from pollutant source or trophic level. Taking these effects into account, advice is provided about sampling and strategies for selection of variables that will improve the reliability of the comparisons between populations.