PhD Research: Contaminants and feeding tracers in North Atlantic killer whales
I just started the final year of my PhD program in the Natural Resource Sciences department at McGill University (Montréal, Québec). My PhD advisor is Dr. Melissa McKinney from McGill University and my co-supervisor is Dr. Robert J. Letcher from Carleton University / National Wildlife Research Center, Environment and Climate Change Canada.
As sentinel species, marine mammals allow us to understand how humans impact the oceans and their ecosystems. They are also essential for the ecological balance of the oceans because their predation affects entire food chains. Yet, chemical pollution and reduced available prey due to climate change are serious threats to their survival. Therefore, understanding the threats to marine mammals is crucial to improving their conservation and allowing human populations who rely on the same ecosystems to prosper.
As the oceans’ top predators, killer whales are threatened by man-made pollutants like industrial chemicals, flame retardants, and pesticides. These pollutants bind to fat and concentrate through the food chains to reach high concentrations in killer whales. A high concentration of these chemicals can cause immune and reproductive problems. But not all killer whales are equally threatened. Whales that feed on marine mammals, like seals and toothed whales, are far more likely to accumulate toxic concentrations of these chemicals than the ones that feed on fish.
Studying killer whales’ feeding ecology is challenging because observation alone cannot reflect long-term habits. Nevertheless, we can use chemical tools to understand killer whales’ diets. To do so, we extract, measure, and compare different elements (lipids and stable isotopes) in whale skin biopsies (skin and fat) and their prey. Using statistical models, we can then reconstruct their diets.
My thesis aims to measure and compare killer whale diets across the North Atlantic Ocean and assess how these diets influence the accumulation of harmful pollutants in their bodies. It will use the biggest number of killer whales ever sampled in the North Atlantic, from Pond Inlet in Canada, to Skjervøy, Norway. Depending on what the whales eat, they will face different risks: health risks due to pollutants, food availability due to climate change, etc. Therefore, it is essential to study their feeding ecology to improve their conservation efforts and help our decision-makers reduce pollution.
So far, I have extracted and quantified fatty acids from 150 killer whale samples, 12 polar bear samples, as well as ~70 prey samples from Iceland and Norway.
I also performed contaminant analyses at the National Wildlife Research Center under the supervision of Dr. Robert J. Letcher. I extracted and analyzed organohalogen contaminants in 64 biopsy samples of killer whales sampled in Iceland. I am currently extracting and quantifying the same contaminants in killer whale samples from Norway, Saint-Pierre & Miquelon and Greenland in my lab at McGill.
Pre-pandemic, my PhD work has allowed me to travel to Iceland, Belgium, Japan, Spain and Norway. I also got to live in Montreal and Ottawa.
Killer whale research collaborators
Icelandic killer whales' diets and their impacts on contaminants
We found that killer whales with a mixed diet, including seals or porpoises, had nine times more contaminants than killer whales that eat fish. It is a significant difference for killer whales within one population. When we looked at the contaminant percentages, killer whales that ate marine mammals had higher percentages of the more persistent and harmful chemicals, characteristic of being higher in the food chain. Still, we know that these killer whales seasonally feed on fish and socialize with fish-eating killer whales. We cannot tell yet how much of their diet includes marine mammals.
We also found that all these “mixed-diet” killer whales had contaminant quantities above all the thresholds for harmful effects. It means that their health could be at risk because they eat marine mammals. This is an important finding because other studies had previously found that the Icelandic population as a whole was not facing health risks.
Most of the killer whales that ate seals or porpoises were the ones that seasonally travel between Iceland and Scotland. As more and more photo-id matches are being found between Iceland and Scotland, we need to continue our research to better understand Icelandic killer whales’ ecology.
Quantitative Fatty Acid Signature Analysis developped for killer whales
We presented a new method to reconstruct wild killer whales’ diets using the lipid composition of their blubber. By measuring these lipids, called fatty acids, in the killer whales’ fat and those in their potential prey, scientists can estimate the abundance of each prey species in the whales’ diet. This new method may hold the key to unlocking the secrets of killer whale diets as they gradually invade the Arctic due to climate change.
To reconstruct the whales‘ diets, we calibrated the model called QFASA using samples from captive killer whales and their prey. We then measured the fatty acid composition of wild Greenland killer whales and potential prey species the whales may feed on. Finally, we applied the modeling approach to estimate that the whales mainly fed on harp and hooded seals, species that we found in some of the whales’ stomachs.
Quantitative fatty acid signature reveals killer whales' diets in unprecedented detail
I wrote multiple stories to summarizes the findings of the third chapter of my doctoral thesis: an open-access peer-reviewed study just published in the Journal of Animal Ecology. You can find the Whale Scientists post here, and the Conversation article here.
Here is a video recap of our main findings. ➡️
MSc Research: Contaminant and feeding niche comparison in two population of Antarctic humpback whales
Humpback whales in the Southern Hemisphere are the sentinels of the Southern Ocean’s health. They carry useful information from their feeding zones all around Antarctica. Since persistent organic pollutants accumulate in food webs, Humpback whales can help us understand which contaminants reach Antarctica and accumulate in Antarctic food webs. To do this, we need to measure the contaminants in their fat, where they are the most abundant.
My thesis aimed to determine southern humpback whales’ feeding habits and measure their contaminant levels to help us measure pollution in Antarctica. I used about 150 whales biopsies sampled in Ecuador and Mozambique, where the whales breed after their migration.
We found long-banned pesticides and industrial pollutants in the blubber of humpback whales from Antarctica, suggesting these contaminants accumulate in Antarctic food webs. However, the pollution levels were some of the lowest measured in the world for these whales.
I analyzed stable isotopes in the University of Liege, Belgium, under the supervision of Dr. Krishna Das. I also measured persistent organic pollutants in the same biopsy samples at the Toxicology Center of the University of Antwerp, Belgium, under the supervision of Dr. Adrian Covaci. I got trained in gas chromatography, contaminant extraction, and purification.My thesis won the best thesis award and resulted in my first peer-reviewed article.
Chemical and Physical Society, University College London – November 2021: Using Dietary Tracers to Understand the Feeding Ecology of North Atlantic Killer Whales, A. Remili
Cetacean Sessions, Bay Cetology – June 2021: You are what you eat, PCBs in North Atlantic killer whales”, A. Remili and C. Andvik