The last link in the food chain in the oceans, orcas are among the most widespread mammals in the world. However, pollution poses a great threat to their future. A recent study shows that half of the world’s population of killer whales, especially those living in the most contaminated areas, has declined rapidly.
Banned from the United States for nearly 40 years and 152 other countries around the world for 17 years, PCBs (polychlorinated biphenyls) continue to contaminate and threaten the environment. Formerly, present in many electrical appliances, insulators, paints, oils, etc., they are very stubborn and persist in the oceans where they often end. More than a million tons would have been widespread since their first use in the 1930s.
Marine microorganisms absorb them, the fish swallow them, the seals ingest them and consequently, their predators, like the killer whale, eat them. In their article published September 28 in the journal Science, researchers are worried about the very high levels of PCBs found in the tissues of these large animals: up to 1,300 milligrams per kilogram have been measured in their fats. Orcas (Orcinus orca) are among the mammals that contain the most in the world. By comparison, a rate of 50 milligrams per kilogram in animal tissues already has a strong impact on their fertility and immune system. “It’s like a killer whale apocalypse” says Paul Jepson, of the Zoological Society of London and co-author of the study.
The researchers are all the more concerned that female orcas don’t reach maturity before the age of 20 and that the gestation lasts not less than 18 months. According to their projections, the world’s population of wild killer whales could be reduced by half in 30 to 50 years in the most polluted areas.
The areas where orcas are most at risk include those bordering Brazil, the United Kingdom and the Strait of Gibraltar. “In these areas, we rarely see newborn killer whales,” said Ailsa Hall, who co-produced the models used by the marine mammal research unit in Scotland.
But that’s not all. PCBs are not the only threat to orcas, there are also microplastics, plus overfishing, noise created by humans… The researchers found that only orcas living far away from pollution, particularly around the Faroe Islands, Iceland, Norway, Alaska and Antarctica, are relatively spared