Predicting global killer whale population collapse from PCB pollution

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Science  28 Sep 2018:
Vol. 361, Issue 6409, pp. 1373-1376
DOI: 10.1126/science.aat1953

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  • Saving killer whale populations from a global collapse
    • Lars Witting, Senior Scientist, Greenland Institute of Natural Resources

    Desforges et al. (2018) address PCB pollution in killer whales, predicting a decline in calf survival and an associated population collapse worldwide. Witting (2018) refutes the collapse showing that it follows from a flawed model parametrisation.

    Desforges et al. (2018) assume that pristine non-polluted killer whale populations can increase at about 0.9% per year. This is unrealistically low because the extensive data of Olesiuk et al. (1990) and Matkin et al. (2014) have shown that killer whale populations that are exposed to small concentrations of PCB can increase at rates between 2.9% and 4.2% per year.

    Assuming a somewhat conservative pristine growth rate from 2.9% to 3.4%, Witting (2018) corrected the analysis to find that killer whales across all pollution levels in Desforges et al. (2018) have the potential for positive growth. There is absolutely no evidence for a global PCB driven collapse of killer whale populations. Yet, the density regulation of the most exposed killer whale populations may compensate only partly for the detrimental effects of PCB.


    Desforges, J.-P., A. Hall, B. McConnell, A. Rosing-Asvid, J. L. Barber, A. Brownlow, S. De Guise, I. Eullaers, P. D. Jepson, R. J. Letcher, M. Levi, P. S. Ross, F. Samarra, G. Vikingson, C. Sonne and R. Dietz 2018. Predicting global killer whale population collapse from PCB pollution. Science 361:1373–1376.

    Matkin, C. O., J. W. Testa, G. M. Ellis and E. L. Saulitis 2014...

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    Competing Interests: None declared.
  • Orcas and PCBs
    • Giovanni Di Guardo, Associate Professor, University of Teramo, Faculty of Veterinary Medicine, Teramo, Italy
    • Other Contributors:
      • Antonio Fernández, Full Professor, Universidad de Las Palmas, Instituto Universitario de Sanidad Animal y Seguridad Alimentaria, Las Palmas, Gran Canaria, Spain

    The dramatic population decline which has been predicted to affect killer whales (Orcinus orca) on a global scale by the end of this century is of concern, with the levels of polychlorinated biphenyls (PCBs) in tissues from free-ranging orcas having been estimated to be among the highest in the animal kingdom (1).
    As in other cetacean and non-cetacean “top predators”, in fact, lipophilic PCBs may heavily accumulate in killer whales’ subcutaneous blubber, thereafter undergoing ad hoc “biomagnification” processes. Since these bioaccumulation and biomagnification dynamics are shared by many other persistent environmental pollutants - either “classical” (i.e. DDTs, dioxins, heavy metals, etc.) or “emerging” (i.e. PBDEs, PFAS, micro- and nanoplastics, etc.) -, that almost unvariably form “mixtures” to which aquatic organisms are chronically exposed via the marine food web(s) (2), one could wonder how the biological effects of PCBs may be effectively “dissected” from those of the other contaminants present in the aforementioned mixtures. Furthermore, the “endocrine disrupting” and the additional pathogenic activities of PCBs on host’s reproductive and immune functions are also known to be exerted by other organochlorine (OC) pollutants, the entry of which into exposed animals’ cells is mediated by aryl hydrocarbon receptors (AHRs) (3). This implies that the susceptibility of a given species to PCBs and, more in general, to OC contaminants could “ideally” result from the “s...

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    Competing Interests: None declared.