Human impacts

The killing of killer whales

This is a guest post by Celine Christiansen, an undergraduate contributor for Oceanbites. She is currently a candidate for a B.S in Biology, focusing on biomedicine, with a minor in English at Providence College. Her interests include Alzheimer’s disease, marine biology, human anatomy and physiology, and language. She enjoys writing and reading, traveling, and volunteering at the animal shelter. In the future, she hopes to either go to graduate school to complete a Physician Assistant program or attend medical school to continue helping others with her multicultural background and ability to speak multiple languages.

Stephen Raverty, Judy St. Leger, Dawn P. Noren, Kathy Burek Huntington, David S. Rotsein, Frances M. D. Gulland, et al (2020). Pathology findings and correlation with body conditions index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013. PLOS One. DOI:

Killer whales, also known as orcas, are protected under the Marine Mammal Protection Act, which was enacted to stall the declination of marine mammals. Killer whales are social and complex marine mammals; they remain close to their offspring throughout their life and even feel grief. These majestic mammals also feel similar emotions that we often experience: they form strong family bonds and experience depression, PTSD, and anxiety, when separated and held in captivity. They have had to adapt to the ever-changing climate, overfishing of wild stocks, marine pollution, and more. While some killer whales suffer from genetic disorders and disease, humans remain the primary source for the death of numerous orcas.

Orca with her 3-month-old killer whale calf. Photo credit: National Geographic, Sea World:

Top predators like killer whales play an important role in balancing our marine ecosystems. In fact, they rank only second to humans as the most widely distributed mammal in the world. Though found mostly in temperate waters, which include the Northern Pacific Ocean, they also appear at river mouths, both of which are subjected to human influences. Considering that killer whales live in oceans that are increasingly impacted by human noise pollution, climate change, and overfishing, it is important to understand how these human interactions affect these charismatic mammals. It is key that we understand how human activities influence the health of these marine mammals, as this information can inform conservation actions and strategies to prevent extinction.

Similar to a scene from CSI or Grey’s Anatomy, one way to understand the health of whales is by performing necropsies, a type of medical examination performed on dead, stranded whales to identify the cause of death. Researchers from the University of British Columbia sought to establish a baseline for understanding orcas’ health, nutritional status, and causes of death by performing necropsies on 53 stranded whales over a decade in the northeast Pacific and Hawaii.

A calf that died due to nutritional deficiency because of a facial malformation. Photo credit: Fig 2 in Raverty et al. 2020

Board-certified veterinary pathologists examined necropsy reports on the dead killer whales to identify the cause of death. The researchers found that five killer whales had severe tooth wear, with two showing nutritional and metabolic deficiencies. They also found that a calf died from a bacterial infection after a halibut hook injury, and two died from trauma received from vessel strikes. Other deaths were likely due to a range of diseases and nutritional deficiencies.

Though there was no single cause of death among the necropsied whales, the study managed to find a common theme in the casualties: all deaths stemmed from human interactions. The study showed that multiple causes may have led to the poor health conditions of the orcas. For instance, the nutritional deficiencies may have reflected the inability of orcas to find enough food. In the case of the calf with a facial deformity, this likely made it more difficult to consume prey. Human interaction was identified in every whale developmental stage, from young calves to older adults. The orca dying due to blunt trauma caused by the vessel illustrates that vessel strikes may be an important threat, especially for endangered species such as the southern killer whales since they stick around areas near humans and shipping lanes. The study illustrates the danger that the ingested fishing hook posed, as it particularly targeted young and inexperienced orcas.

A pair of playful killer whales. Photo credit: ABC News

The study establishes a link between human interaction and orca deaths. It is important to utilize this information and navigate with caution to protect and conserve killer whale populations. The researchers acknowledge that there is much more to study to fully grasp the cause of mortality of the orcas in order to develop a solution to reduce deaths going into the future. Necropsies can only be performed on whales that are found in good condition, and even then, it is difficult to truly rule on the cause of death. However, the study highlights the human and environmental factors that can be detrimental to the health of killer whales. With this information, we can form strategies to protect our beloved marine mammals and their families.

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