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Dolphins, whales and human pollution
2/13/17

Humpback whales from the warm waters of the Indian Ocean reveal pollution from... Antarctica! 

Humpback whales are known for travelling far and wide. They can be found in all the planet's seas, including the Indian Ocean. They come to the warm waters of Reunion Island between the months of June and November to give birth and nurse their young. For the rest of the year, the whales are present in the nearshore waters of Antarctica, more than 8000 km away from Reunion Island. Here, the whales feed in the cold waters, mainly on krill, a small species of crustacean that is highly prized by these great mammals. Krishna Das, in collaboration with the Groupe Local d'Observation et d'Identification des Cétacés (GLOBICE, Dr. V. Dulau) and the Toxicological Centre at the University of Antwerp (Prof. A. Covaci), among others, focused on the exposure to pollutants of the tested humpback whales around Reunion Island (2). 

Biopsy whales

As humpback whales mainly feed in the Southern Ocean (and not in the Indian Ocean), they accumulate the pollutants present in Antarctica in their tissues. Despite Antarctica's distance from any human activity, we can nevertheless detect industrial pollutants and pesticides used many thousands of kilometres away in many marine species. 

And the humpback whales of the Indian Ocean are sadly no exception. The researchers found detectable concentrations of pesticides in their blubber, as well as molecules used by industry (polychlorinated biphenyls, PCBs) and flame retardants (polybrominated diphenyl ethers, PBDEs). The use of these pollutants is forbidden but these organic molecules are highly resistant, don't disintegrate and accumulate in living organisms. 

However, the humpback whales of the Indian Ocean are less contaminated than their fellow creatures of the northern hemisphere because they mainly consume krill and consequently occupy a lower position in the food web (whales from the north also eat fish). Furthermore, the humpback whales of the southern hemisphere are further away from human activity, mainly based in the northern hemisphere. 

Another interesting fact is the variability of pollutant concentrations in whales from the southern hemisphere. When comparing the results with several earlier studies, the researchers noticed that despite lower contamination levels in the Antarctic ecosystems, some whales showed relatively high levels. There are a number of reasons: age, sex, diet, and the redistribution of organic pollutants during their migration and when giving birth and nursing. The humpback whales of the southern hemisphere don't feed at all, or very little, during their stay in the waters of Reunion Island and during their return journey. A true physiological challenge and a rather unique toxicological model! 

(2) Linking pollutant exposure of humpback whales breeding in the Indian Ocean to their feeding habits and feeding areas off Antarctica, Das K. et al. Environmental Pollution, Jan. 2017. 

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