A recent study published describes the catastrophic global population collapse of killer whales
Photo by Byran Goff (Unsplash)
by Anton Kuech
Killer whales (Orcinus orca) are the apex predators of the sea and the largest species in the dolphin family. Males can reach sizes of up to 10m, weighing 10,000 kg. They are known to live up to near human-length lifespans, with females living up to 80 years. The world’s oldest known orca, spotted off the west coast of Canada, died in 2017 at the age of 105. In contrast, the lifespans of orcas in captivity are greatly reduced, with, for example, the average age of death for orcas at SeaWorld at 14 years. Killer whales are distributed throughout all oceans and their diet ranges from fish to marine mammals, leading to a range of killer whale ecotypes.
Orcas are known for their sophisticated intelligence and emotions. They communicate and hunt by echolocation, making distinctive noises; each pod has a unique ‘dialect’ that its members recognize. Their hunting methods are extremely elaborate, with, for example, orcas in Argentina swimming onto shore to catch sea lion pups or pod members in the Antarctic coordinating large waves to wash seals from ice floes. Lori Marino, a neuroscientist prominently featured in ‘Blackfish’, pointed out that orcas have an extra lobe of tissue which is absent in human brains and most likely responsible for processing emotions.
Killer whales have often been portrayed in popular culture, appearing in several books, movies and documentaries, most famously being the movie, ‘Free Willy’, a 1993 film based on a lonely boy who saves a whale from a rundown theme park. Keiko, a killer whale held in a Mexican theme park, starred as Willy. The real living conditions of Keiko sparked global outrage and money was raised to help Keiko adapt to life in the wild. The story tragically ended with Keiko’s death at age 27, somewhere near Norway.
Human activities threaten a variety of orca populations, with habitat loss, noise pollution and decreasing prey abundance previously identified as the main threats. A new multi-national study on the effects of PCB pollution on killer whale populations has found that more than 50% of killer whale populations are threatened. Polychlorinated biphenyls (PCBs) are toxic anthropogenic compounds that impair reproduction, weaken the immune system and increase the risk of cancer in vertebrates. Even though PCBs were banned around 30 years ago, the chemicals persist in many long-lived wildlife species. Orcas are the apex predators of the seas and their place in the food chain is partly responsible for their demise. Populations feeding on higher-trophic level organisms (e.g. seals) accumulate higher concentrations of PCBs in their blubber and thus, are most vulnerable. According to the study’s prediction, populations in close proximity to humans are likely to experience complete collapse, whereas those around the Arctic and Antarctic appear sustainable.
Altogether, the study sets out a dire outlook on the future of this fascinating species. More than 80% of global PCB stocks still haven’t been destroyed, yet unmeasured contaminants have been identified in killer whale tissues that may further decrease reproductive function. PCBs alone are likely to cause the extinction of over 50% of the current killer whale populations, and one can only imagine how dark the future for killer whales looks when accounting for all threats this species faces.
