Preying on marine mammals might be threatening the survival of Icelandic orcas

Scientists have for a long time thought that orcas in Iceland specialized in eating fish (like herring). Recently, however, experts have noticed that some Icelandic orcas seem to enjoy another type of snack: marine mammals. This could be a problem, and eating marine mammals could threaten the long-term survival of these orcas. In this post, I explain the results from the first paper of my PhD, looking at contaminants in Icelandic orcas.

icelandic orcas
An Icelandic orca – Photo taken by Filipa Samarra / Icelandic Orca Project

Environmental contaminants and orcas

Here is the problem: environmental contaminants (like PCBs) released by humans enter the water and amplify throughout the food chain. Orcas are at the top of the food chain, and we know that the ones that eat marine mammals tend to accumulate more harmful chemicals than those eating fish. This is because eating marine mammals adds another step in the food chain and another round of contaminant amplification. Because of these high levels of chemicals, experts have predicted that 50% of the orca populations could be facing population reductions. Indeed, these contaminants affect both the immune and reproductive systems in marine mammals. So, by accumulating large quantities of these chemicals through their diet, orcas put their health at risk.

Studying orcas in Iceland

Coming back to our Icelandic orcas, we wanted to study the relationship between the diet of different individuals and see if eating marine mammals would put some orcas’ health at risk. To do so, we collected biopsies from 50 orcas all around Iceland. We grouped them into two categories based on their diet. We used both photos and chemical tools (stable isotopes) to classify them that tell us how high the orcas are in the food chain. Next, we measured the quantities of contaminants in their fat (where the contaminants accumulate).

icelandic orcas
A pod of orcas in Iceland – Photo was taken by Filipa Samarra / Icelandic Orca Project

We found that orcas with a mixed diet, including seals or porpoises, had 9 times more contaminants than orcas that eat fish. This is a large difference for orcas within one population. When we looked at the contaminant percentages, orcas that ate marine mammals had higher percentages of the more persistent and harmful chemicals, which is characteristic of being higher in the food chain. Still, we know that these orcas seasonally feed on fish and socialize with fish-eating orcas. We cannot tell yet how much of their diet includes marine mammals. Based on their contaminant concentrations and signatures, we know for sure that they feed on them at least enough to accumulate all these harmful chemicals. Ecology is always more complicated than we first expect it to be…

Icelandic orcas at risk?

We also found that all these “mixed-diet” orcas had contaminant quantities above all the thresholds for harmful effects. It means that these orcas’ 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. But because Icelandic killer whales’ ecology is more complicated than what we previously thought, we recommend focusing on the differences between individuals to identify which ones face health risks.

icelandic orcas
An Icelandic adult male with a juvenile – Photo was taken by Sara Tavares / Icelandic Orca Project

Most of the orcas that ate seals or porpoises were orcas that seasonally travel between Iceland and Scotland. Experts think these orcas eat seals when in Scotland, which could threaten their health. As more and more photo-id matches are being found between Iceland and Scotland, we need to continue our research to understand Icelandic killer whales’ ecology better.

Thank you for reading!

Thank you for reading about my first paper’s findings. This post means the world to me, as it took me two years to conduct and publish this study. Here is the link to my paper for those who want to check out the academic version of this post in the journal Environmental Science and Technology:

Here is the link to the Icelandic Orca Project website. They are our collaborators in this study and the ones that collected the samples we used. They do an amazing job on Icelandic orcas. You can find all their contact info below:

If you want to find out about some of my previous work on contaminants in humpback whales from Antarctica, please click here.

If you wish to contact me to get access to our study or if you have any questions/comments, please reach out:

Anaïs is the founder of Whale Scientists. She is a PhD student at McGill University working on killer whale ecology and pollution. You can read more about her here.

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