Predicting global killer whale population collapse from PCB pollution

Abstract

Killer whales (Orcinus orca) are among the most highly polychlorinated biphenyl (PCB)–contaminated mammals in the world, raising concern about the health consequences of current PCB exposures. Using an individual-based model framework and globally available data on PCB concentrations in killer whale tissues, we show that PCB-mediated effects on reproduction and immune function threaten the long-term viability of >50% of the world’s killer whale populations. PCB-mediated effects over the coming 100 years predicted that killer whale populations near industrialized regions, and those feeding at high trophic levels regardless of location, are at high risk of population collapse. Despite a near-global ban of PCBs more than 30 years ago, the world’s killer whales illustrate the troubling persistence of this chemical class.

Saving killer whale populations from a global collapse: rebuttal against Desforges et al. (2018)

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In their Science paper, Desforges et al (2018) address PCB pollution in killer whales, predicting a decline in calf survival and an associated collapse of killer whale populations worldwide. I refute the collapse, showing that it follows from a flawed model parametrisation.

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“…Equally important is an environmental model to predict future ecological exposures to PCB. These regulation issues, however, are not addressed by Desforges et al (2018), who consider unregulated population growth with constant PCB contamination in the different exposure groups. This makes their study unable to predict realistic killer whale dynamics, but it does not imply that they are unable to estimate current impacts on killer whales worldwide.Their figure 2A illustrates this impact by a calf survival that declines with increased maternal PCB concentration.…”

Investigating decadal changes in persistent organic pollutants in Scottish grey seal pups

“…POPs have also recently been connected with lipid disruption in a range of phyla (Lee et al, 2016;Speranza et al, 2016;Yadetie et al, 2017), including marine mammals (Castelli, Rusten, Goksøyr, & Routti, 2014;Robinson et al, 2018;Tartu et al, 2017), because they alter pathways that enable individuals to accumulate or mobilize fat reserves appropriately. It has been proposed that marine wildlife populations with high POP burdens may be unable to reproduce or survive as a result of chronic POP effects (Helle et al, 1976b;Ross, 2006), potentially preventing population recovery in some declining species (AMAP, 2018;De Guise, Martineau, Béland, & Fournier, 1995;Desforges et al, 2018;Noël, Barrett-Lennard, Guinet, Dangerfield, & Ross, 2009). It has been proposed that marine wildlife populations with high POP burdens may be unable to reproduce or survive as a result of chronic POP effects (Helle et al, 1976b;Ross, 2006), potentially preventing population recovery in some declining species (AMAP, 2018;De Guise, Martineau, Béland, & Fournier, 1995;Desforges et al, 2018;Noël, Barrett-Lennard, Guinet, Dangerfield, & Ross, 2009).…”

“…In natural environments, POPs are readily bioaccumulated up through food chains to generate high concentrations in top predators (Johnson-Restrepo, Kannan, Rapaport, & Rodan, 2005), such as marine mammals (Helle, Olsson, & Jensen, 1976a;Ross, Ellis, Ikonomou, Barrett-Lennard, & Addison, 2000). They have the potential to negatively impact marine wildlife, and remain a conservation concern for marine mammal species worldwide (AMAP, 2018; Desforges et al, 2018;Jepson & Law, 2016;Law et al, 2012). POPs such as CBs, BDEs, and organochlorine pesticides (OCPs), including dichlorodiphenyltrichoroethane (DDT), have been linked to endocrine disruption (Noël et al, 2017;Routti et al, 2010;Tanabe, 2002;Villanger et al, 2011Villanger et al, , 2013 and negative impacts on reproductive (Helle, Olsson, & Jensen, 1976b;Hoydal et al, 2017;Murphy et al, 2010;Reijnders, 1986) and immune (Fisk et al, 2005, Hall et al, 2006, Hammond, Hall, & Dyrynda, 2005, reviewed in Desforges et al, 2016Penin et al, 2018) function in marine mammals.…”

“…Viable immune and endocrine function, successful reproductive efforts, and the ability to use energy stores are all crucial to the fitness and survival of individuals in the wild. It has been proposed that marine wildlife populations with high POP burdens may be unable to reproduce or survive as a result of chronic POP effects (Helle et al, 1976b;Ross, 2006), potentially preventing population recovery in some declining species (AMAP, 2018;De Guise, Martineau, Béland, & Fournier, 1995;Desforges et al, 2018;Noël, Barrett-Lennard, Guinet, Dangerfield, & Ross, 2009). POPs may negatively impact on juvenile survivorship (Hall, Thomas, & McConnell, 2009), even in populations that are increasing or stable in size, such as UK grey seals, Halichoerus grypus (SMRU, 2017).…”