Some human impacts are much more discreet than hunting and by-catch. They may not kill directly, and their impact is more difficult to assess, but their long-term effects might be detrimental at the population level. Pollution and ocean acidification are such “soft” or “silent” killers.
Pollution is the introduction in the natural environment of an unnatural constituent, substance or energy, that causes adverse effect. It can take the form of chemical substances (such as contaminants and oil spills), energy (such as noise) and debris (such as plastic, nets, rubber and other persistent trash). Some pollution is naturally occurring but the vast majority originates from human activities.
Marine pollution poses a chronic, vast, dynamic and growing threat to the marine environment and marine mammals. It mostly consists of substances (contaminants, plastic, fishing gears) that degrade slowly, if at all. The continuous input of large quantities of all kinds of pollutants means a gradual build-up in the marine environment, so the situation is continuously worsening. Pollution by polychlorinated biphenyl (PCBs) continues to impact populations of marine top predators in European waters long after their production and use were banned in Europe in the mid 1980s. Reproductive failure observed today in European harbour porpoise, killer whale and bottlenose dolphin populations has been correlated to their PCBs burdens.
But pollution does not stay in European waters – it travels to the Arctic. Marine pollution such as persistent organic pollutants (POPs) and mercury undermines food quality, sometimes with levels above accepted standards for human consumption. The high level of contaminants in some marine mammals has led the Health Authorities in the Faroe Islands and Greenland to recommend a reduced intake of marine mammal meat and a 0-intake for some specific groups.
Contaminants or chemical pollutants represent a significant threat to the environment and marine mammal populations. Environmental contaminants affect the reproductive, immune and nervous systems of organisms. In Svalbard, 1.5% of polar bear females have partially-developed male sexual organs – pseudohermaphrodites, and in East Greenland, polar bears exhibit reduced bone density (osteoporosis) and size reduction in sexual and reproductive organs, both linked to high concentrations of environmental contaminants.
You can read more on contaminants here.
Marine debris in the ocean, especially plastic debris, is an increasing environmental issue globally. Between 5 and 12 million metric tons of plastic are dumped in the ocean every year from coastal countries. Plastic debris injures and kills many marine life, including marine mammals, through entanglement and ingestion. Over 50% of all marine mammal species have suffered from ingestion of marine debris or entanglement.
You can read more on marine debris here.
Microplastics are tiny plastic particles ranging from 5 mm in diameter to nano proportions. They are turning up in all the major oceans, including the Arctic and Antarctic, and are likely the most numerically abundant items of marine plastic debris. They are ingested by filter-feeding marine organisms such as oysters and mussels, but also the filter-feeding baleen whales, potentially inducing a reaction within the tissue.
You can read more on microplastics here.