Abstract :
[en] 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.
