Individual Prey Specialization Drives PCBs in Icelandic Killer Whales

Abstract

Interindividual variation in prey specialization is an essential yet overlooked aspect of wildlife feeding ecology, especially as it relates to intrapopulation variation in exposure to toxic contaminants. Here, we assessed blubber concentrations of an extensive suite of persistent organic pollutants in Icelandic killer whales (Orcinus orca). Polychlorinated biphenyl (PCB) concentrations in blubber were >300-fold higher in the most contaminated individual relative to the least contaminated, ranging from 1.3 to 428.6 mg·kg–1 lw. Mean PCB concentrations were 6-to-9-fold greater in individuals with a mixed diet including marine mammals than in fish specialist individuals, whereas males showed PCB concentrations 4-fold higher than females. Given PCBs have been identified as potentially impacting killer whale population growth, and levels in mixed feeders specifically exceeded known thresholds, the ecology of individuals must be recognized to accurately forecast how contaminants may threaten the long-term persistence of the world’s ultimate marine predator.

Validation of quantitative fatty acid signature analysis for estimating the diet composition of free-ranging killer whales

“…Previous studies suggested that some populations of North Atlantic killer whales are strongly associated with mackerel stocks 7 . Since killer whales are opportunistic hunters capable of switching prey 6 , one could easily imagine killer whales in Greenland having a mixed diet of both mackerel and seal species.…”

“…Similarly, stomach contents and fecal samples are both challenging to obtain, only represent recent feeding patterns and, in the case of stomach contents, can only be obtained from deceased individuals that may not represent the healthy part of the populations 4 . Thus, the use of chemical tracers measured largely from biopsies collected remotely from cetaceans has increased in recent decades due to relative ease of sampling and ability to reflect integrated diet signals over time 5 , 6 . Stable isotopes of carbon and nitrogen in the skin have revealed some inter and intra-population variation in the feeding patterns of cetaceans, providing diet composition estimates mostly at the trophic level, although species-level precision from stable isotopes remains challenging 7 – 9 .…”

Cross-Generational Impacts of Diet Shift on Bisphenol Analogue Loads in Indo-Pacific Humpback Dolphins (Sousa chinensis)

“…As the top predators in the PRE, dietary uptake of humpback dolphins is the main route for the accumulation of contaminants. Thus, altered prey consumption imposes potential influences on their contaminant exposures. − For the PRE humpback dolphins, a demographic study indicated a reduction of around 2.5% in population size per year . Contaminant exposure was reported to be highly associated with population decline via compromising the immune functions and reproduction. , However, the load of endocrine-disrupting chemicals in response to altered prey consumption patterns in humpback dolphins has not been characterized.…”

Ecotoxicological Characterization of Type C Killer Whales From Terra Nova Bay (Ross Sea, Antarctica): Molecular Biomarkers, Legacy, and Emerging Persistent Organic Contaminants

“…than the levels in Norwegian fish-eating killer whales (429 mg/kg l.b. ), hundred-fold lower than mixed-diet killer whales (Remili et al, 2021), and well below the lowest value (9.0 mg/kg l.b.) proposed as the toxicity threshold concentration for the onset of physiologic effects in marine mammals (Kannan et al, 2000;Jepson et al, 2016).…”

“…Generally, POPs experience biomagnification within food webs since dietary intake acts as the main route for contaminant accumulation. Thus, high levels of POPs have been documented in killer whales from different geographical areas (mostly from the northern hemisphere; Desforges et al, 2018;Andvik et al, 2020;Lawson et al, 2020;Remili et al, 2021). Substantial differences due to their ecotype (based on prey specialization) influence the accumulation of contaminants in killer whales, which may exert different effects on different populations worldwide (Desforges et al, 2018).…”