Persistent organic pollutants in humpback whales from the southern hemisphere: influence of stock and trophic ecology.
Supervisor: Krishna Das (Univ. Liege).
The southern hemisphere humpback whales, Megaptera novaeangliae, have been extensively studied throughout the past years. Although we learned a lot about these whales, little is known about their trophic niche and their contaminant burden. We know southern hemisphere whales undergo large scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter grounds in the subtropical to tropical regions. The aim of this study was to understand the isotopic niches and persistent organic pollutants (POPs) burdens of Humpback whales from two stocks: stock C1 breeding off Mozambique and stock G breeding off Ecuador. We focused our analysis on the main POPs; polychlorinated biphenyls (PCBs), pPolybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) including dichlorodiphenyltrichloroethane and its metabolites (DDXs), hexachlorobenzene (HCB), lindane (HCHs), chlordanes (CHLs) and methoxylated PBDEs (MeO-PBDEs). Analyses of stable isotopes δ13C and δ15N in skin resulted in further insight on their feeding ecology, which was in agreement with a diet focused mainly on low trophic level prey species, such as krill from Antarctica, Euphausia superba. However, one group in the C1 stock had higher δ15N values that could be explained by sex, metabolic state, age or geographic δ15N variations, or a more opportunistic diet in Antarctica that includes fish. No significant differences in δ34S were found. POPs were measured in all humpback whales in the order of HCB > DDXs > CHLs > PCBs > HCHs > PBDEs > MeO-PBDEs. HCB (mean : 66.5 ng/lw in Mozambique and 36.5 ng/lw in Ecuador) and DDXs (mean : 8 ng/lw in Mozambique and 24 ng/lw in Ecuador) were the predominant compounds in all humpback whale samples. HCB accounted for 81% of POPs in Mozambique and 54% in Ecuador while DDXs accounted for 10% of POPs in Mozambique and 35% in Ecuador. Among DDT compounds, p,p’-DDE was the major pollutant, reflecting its long-term accumulation in humpback whales. Significantly higher concentrations of HCB were found in whales from Mozambique while significantly higher concentrations in DDXs and HCH were found in whales from Ecuador. No significant differences were found in PCBs between the two populations. Levels in POPs were in accordance with other studies from the southern hemisphere and were in each case lower in the southern hemisphere than in the Northern hemisphere. Pollutants were not correlated with δ15N, lipid content in the blubber or time. It may indicate different exposures of the whales according to their feeding zones. Further investigations are required to assess exposure of southern humpback whales throughout their feeding zones.