Threats to the World’s Oceans: Pollution and Over-Fishing – 20th and 21st centuries

During the 20th century, our oceans were fouled by pollution of all kinds and now contain increasing numbers of dead zones, where pollution-fed algae deprive existing marine life of oxygen. Oil spills from tankers are the most visible manifestation of pollution, but make up only a small percentage of the total. As holidaymakers avoid flying to limit their carbon footprints, more and more cruise liners take to the seas, and these floating towns discharge millions of gallons of detergent-laden ‘grey water’, oily bilge water and raw sewage. Even worse is the effect of runoff pollution: all over the world, a toxic cocktail of chemicals from factories and agriculture, along with the steady drip of oil from engines of all sorts, slowly but surely leaches into the water. We also toss waste of all kinds directly into the sea where floating plastic litter kills millions of seabirds, marine mammals and fish.

We also kill fish intentionally, and the 20th century population explosion greatly increased demands on fish stocks worldwide, resulting in the near extinction of several species. Quotas and controls may have saved some, such as cod and tuna, but marine biologists are concerned by the decrease in variety of species, as well as numbers, in the fishing grounds. Invasive and indiscriminate fishing methods endanger not just fish, but also ocean life – deep trawling, for example, destroys the fragile ecosystem of the seabed, where unknown species are still occasionally discovered.

The oceans cover 70 per cent of our planet and remain largely unexplored. We know more about outer space than we do about what goes on in the depths of the ocean, and we are only just beginning to appreciate both the importance and the vulnerability of our oceans and seas. As the warnings of environmentalists start to be heeded, we just have to hope it is not already too late.

When: 20th and 21st centuries

Where: Worldwide

Toll: incalculable

You should know: In 1992 a cargo of thousands of brightly colored bath toys fell into the Pacific; they spent nearly a year in the Subpolar Gyre, a counter-clockwise current, before circling the Pacific. For more than ten years, flotillas of yellow ducks were tracked as they journeyed around the world in different directions. They have been valuable to oceanographers studying currents and a delight to beachcombers who find them.