PERSISTENT ORGANIC POLLUTANTS IN HUMPBACK WHALES FROM THE SOUTHERN HEMISPHERE: INFLUENCE OF GENDER, STOCK AND TROPHIC ECOLOGY

Abstract

Humpback whales, Megaptera novaeangliae, from the southern hemisphere undergo large scale seasonal migrations between their summer feeding grounds near Antarctica and their winter reproductive grounds in the subtropical to tropical regions. However, population structure data in the southern hemisphere is scarce. The aim of this study was to get information on stocks structure in the Southern hemisphere using chemical tracers; stable isotopes and persistent organic pollutants (POPs) concentrations in Humpback whales from two stocks: stock C1 breeding off Mozambique and stock G breeding off Ecuador. Material and methods: Skin and blubber biopsies of humpback whales from Ecuador (2014-2015, n= 60) and Mozambique (2017, n=89) were sampled. δ13C and δ15N values were analyzed in skin. POPs were analyzed in the blubber: polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) including dichlorodiphenyltrichloroethane and its metabolites (DDXs), hexachlorobenzene (HCB), lindane (HCHs), chlordanes (CHLs) and methoxylated PBDEs (MeO-PBDEs). Gender was determined genetically (see Das et al. 2017 for detail in methodology). Results: Low δ13C and δ15N values in skin reflected their diet focused mainly on low trophic level prey species, such as krill from Antarctica, Euphausia superba. One group in the Mozambique stock had higher δ15N values. Gender did not account for this variation. Other driving factors could be the metabolic state, the age, the geographic δ15N variations in feeding grounds, or a more opportunistic diet in Antarctica that includes small fish. The isotopic niches from Mozambique and Ecuador did not overlap indicating that the two populations exploit different resources. The differences in δ13C (p-value < 0.01) between the two populations suggested a different geographic source of primary productivity meaning the whales do not feed in the same area. However, female humpback whales in Ecuador had significant lower δ15N (p-value < 0.01) and δ13C (p-value < 0.01) values than males maybe suggesting different feeding habits between males and females within this population. POPs were measured in 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. Significantly higher concentrations of HCB were found in whales from Mozambique (p-value < 0.01). Significantly higher concentrations in DDXs (p-value < 0.01) and HCH (p-value < 0.01) were found in whales from Ecuador. Among DDT compounds, p,p’-DDE was the major pollutant, reflecting its long-term accumulation in humpback whales. 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. However, males had significantly higher HCB (p-value < 0.05), PCBs (p-value < 0.01) and CHLs (p-value < 0.01) concentrations than females. Conclusions: While gender seems to be the main reason for POP variation, the feeding zones also need to be considered as a factor of POPs variation. Further investigations are required to assess exposure of southern humpback whales throughout their feeding zones