Why do cetaceans die?

Cetaceans can simply die from old age. Their lifespan ranges from a few decades for harbour porpoises to over 200 years in case of bowhead whales. They can also die from predation from  killer whales, polar bears or from sharks. This is especially prevalent in smaller species and calves of larger whales that are easy targets for the marine mammal predators.

Not only that, newly weaned and inexperienced individuals can easily get lost and become stranded. Furthermore, live individuals can die naturally from asphyxiation during individual and mass stranding events. In November, 2018, multiple stranding events occurred all over New Zealand: 145 pilot whales stranded on a beach on Stewart Island, 10 pygmy killer whales stranded at Ninety Mile Beach and a sperm whale was also found dead on Tokeroa Beach.

Moreover, whales can die from diseases, parasites and even difficulties during birth, just like us. Between 2009 and 2012, close to half of all St. Lawrence Estuary belugas that died were infected with Toxoplasma gondii—a parasite found in cats. Though the study did not find toxoplasmosis to be the primary cause of death in the stranded belugas, it could have resulted in a compromised immune system making them prone to diseases, including neurological deficits.

All these natural events, however, can sometimes be heightened by some threats posed by human beings.

Anthropogenic Causes

Studies prove that anthropogenic (human-caused) effects are the leading cause of mortality in certain species of cetaceans. These can be further divided into two: direct and indirect.

Following are a few of the anthropogenic effects that have a direct impact on cetaceans worldwide.

Following are a few of the anthropogenic effects that have an indirect effect on cetaceans worldwide.

• Chemical contaminants, such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), pollute the marine environments and have been proven to be concentrated in the blubber layers of many cetaceans. Because of biomagnification—a phenomenon with which toxins and other substances increasingly accumulate at each trophic level of the food chain—cetaceans are at risk.
• Starvation from reduced prey availability due to overfishing or plastic ingestion causes cetaceans to slowly die. In a state of starvation, their bodies also start using up stored fat reserves, which makes matters even worse for them as it is these fat reserves that house the lipid-loving chemical contaminants.
• Climate change also affects them. For instance: reduced sea-ice cover and increased temperatures result in reduced prey availability and changes in migration patterns. Not to mention that depleting sea-ice cover is making way for more and more vessels in what were previously hard to navigate areas in the Arctic—exposing more cetaceans to potential vessel strikes. To add to that, increase in temperature affects many endemic species that have temperature specific habitat requirements.