ProjectThe role of feeding ecology in persistent organic pollutant exposures of killer whales (Orcinus orca) across the North Atlantic Ocean
Chemical pollution is one of the nine critical global threats to wildlife and human health in the Anthropocene era. A type of human-made chemicals called "persistent organic pollutants" (POPs) includes long-banned industrial chemicals and pesticides. These chemicals still circulate in our oceans, even decades after their ban. They associate with fat and accumulate through the food web to reach high concentrations in cetaceans. These contaminants' high levels cause health issues: altered immune, endocrine, reproductive functions, and even cancer. Many whales and dolphin populations have POP concentrations above thresholds for health issues. One species that showed the highest levels of POPs is the killer whale (Orcinus orca). A recent study suggested that half of killer whales populations could disappear by 2100 due to their POP concentrations. However, the study used a limited number of killer whales; therefore, we need to assess the levels, toxicity, and risks associated with POPs for all killer whale populations. The diet is the main factor of POPs accumulation. However, there is not much information on killer whales' diets or their exposure to pollutants in the North Atlantic, despite their large population size (thousands of individuals). No study to date has compared the diet between all North Atlantic killer whale groups. Previous studies have proposed two killer whale ecotypes in this region. Type 1 killer whales feed on fish, and type 2 killer whales supposedly feed on marine mammals. Yet, recent studies showed that individuals in all killer whale groups in the North Atlantic Ocean seem to feed on different prey. Some "type 1" killer whales feed on marine mammals while some "type 2" whales eat fish. It seems there are variations in the whales' diet, on both intra-population and inter-population levels. Marine mammals are typically higher in the food web and accumulate more toxic chemicals than fish. It means that some individuals feeding on marine mammals might be at risk from contaminants. Studying killer whales' diet is difficult because observing the whales' predation in harsh weather is complicated. Plus, we would need to be always at sea to follow them, which is impossible. Fortunately, we can use chemical tracers to understand killer whales' diets. We need to extract, measure, and compare different elements (lipids and stable isotopes) in whale skin biopsies (skin and fat). My thesis's primary goal is to measure and compare killer whale diets across the North Atlantic Ocean and assess how diets influence the whales' POPs accumulation. 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 diet to improve conservation efforts for this charismatic top predator. The tools we develop in my thesis will also help investigate their future dietary shifts caused by climate change. We know some killer whales are starting to invade the Arctic, and they likely started feeding on local prey. Getting precise information on their diets will be critical to assess their impact on Arctic ecosystems.