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Dirty water and biomagnification

Humans leave a legacy in the ocean. Because of the way we live, whales that die in our waters are often polluted enough to qualify as toxic waste.

A pink coloured translucent piece of plastic floating in the water above a rocky seafloor

When thinking about the unfathomable depth and breadth of the world’s oceans, it can feel like any pollutants from humans that wind up there must be diluted beyond carrying any risks. And while in some ways this is true, it’s also not the reality when considering the way a food web and its environment interact.

Organochlorines

One particularly worrisome class of chemical pollutants are organochlorines, such as PCBs. These have been widely used as insecticides; as a sheep dip, for treating timber, and within the home, among other uses. Many of these substances do not break down easily and persist in the environment.

Substances like these find their way into all levels of the food chain and persist in the body. Every time a predator eats its prey, it accumulates all the toxin load its prey has accumulated (and the load of its prey’s prey before it). Whales (and humans) are at the top of their respective food chains, meaning they wind up with the highest toxin level.

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This content is taken from
Museum of New Zealand Te Papa Tongarewa online course,

The Significance of Whales to Aotearoa New Zealand

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Though these compounds were restricted in the 1970s and banned in Aotearoa New Zealand in 2004, 20% of PCBs ever made have found their way into the ocean, and into the systems of the creatures that live there. According to the Department of Conservation:

The World Health Organisation standard classifies any material with a PCB level of 50 parts per million (ppm) as highly toxic waste. Levels of organochlorines found in marine mammals in some parts of the world far exceed this level.

Biomagnification

The video below, by Whale and Dolphin Conservation UK, helps explain the concept of biomagnification, and why pollutants (particularly those from industry and agriculture) are of such particular risk to cetaceans and other apex predators of the ocean.

It is also a fine example of the efforts such organisations make to educate the public on these issues, often appealing to our emotions in an effort to break through the media saturation that often leaves us disconnected from the natural world and our impacts on it.

This is an additional video, hosted on YouTube.

Though Lulu’s story focuses on her chemical-induced inability to have calves, the situation is just as dire for those that do. Many of these accumulated contaminants end up being stored in the animal’s blubber, and are released back into the system – where they can do greater damage – during times of stress or higher energy output.

Both cases are especially relevant for pregnant and nursing mothers. The foetus is first exposed to these circulating toxins in utero and then even more as the mother burns off huge amounts of blubber to produce high-fat milk for them in their first months or years. This means the calves begin life with a high burden of chemical toxins that only builds for the rest of their lives.

Climate changes

Other forms of pollution and changing weather patterns contribute to huge toxic algal blooms, made up of some of the most potent natural poisons in the world. These ‘red tide’ blooms can and have killed whales en masse in Europe and the Americas.

Changes to the climate threaten whales in a number of other ways too; the depletion of ozone protection, changes in sea temperature and salinity, and the depletion of key food sources such as krill.

Plastic ocean

Plastic waste is a massive killer of cetaceans too. UNESCO estimates that 100,000 marine mammals die because of plastic pollution each year.

Plastic waste can look like prey; a plastic bag drifting in the current is easily mistaken for a passing squid by a hungry whale. The problem is that much of this plastic does not pass through the whale, instead slowly accumulating, filling its stomach. Eventually this means the whale feels permanently full, stops feeding, and dies of starvation and thirst (whales absorb their water from their food).

The scale of the problem is as hard to fathom as the size of a blue whale. According to the World Wildlife Fund in 2021:

Currently, more than 11 million metric tons of plastic are flowing into the ocean each year. By 2050, there could be more plastic in the sea by weight than fish.

Cetaceans are far from the only animals dying in droves from plastic pollution. As consumers, it’s on each one of us to become more conscious of how we buy, use, and dispose of plastic packaging.