They then subjected the samples to contaminant analysis. Ross et al. were therefore able to analyze contamination patterns in relation to sex, age and subpopulation. The sexual differences observed are consistent with reports from other cetaceans. Females unload accumulated PCBs by transferring them to offspring, first in the womb and then via lactation. Other studies have shown that cetacean females off-load the majority of their organochlorine burden to their calf during reproduction, mostly via lactation.
Males have no comparable mechanism.
An analysis of contamination by age showed that contamination declines in females at the age of first calving and remain low in females until the reach approximately 50 yrs of age. Afterwards contamination once again begins to accumulate. The greater concentrations observed in 'transients' is a result of dietary differences. Eating other marine mammals, 'transients' are one level higher in the food chain. They eat predators of salmon whereas the residents eat salmon directly.