Marine debris (or litter) is commonly defined as human-created persistent solid material that is manufactured or processed and directly or indirectly, deliberately or accidentally, disposed of or abandoned into the marine or coastal environment (UNEP 2016). This ranges from plastic bags, soda cans to ruined/old fishing gear and abandoned vessels. Marine litter – especially plastic debris in the ocean – is a major global environmental issue (ibid.). Between 5 and 13 million metric tons of plastic enter the oceans annually (Jambeck et al. 2015). Only 14% of plastics are currently effectively collected for recycling, while another 14% is incinerated and/or recovered into energy on a global average (NPI 2018). 40% end up in the landfill while the resting 32% ends up in the ecosystems (ibid.), including the ocean.The total of plastic in the ocean is estimated to weight more than every blue whale left in the world’s ocean today (IWC 2020).
Like other pollutants, marine debris lives its own life, following currents and winds, and ending-up far away from their sources. It is found floating in all the world’s oceans, everywhere from polar regions to the equator, even in remote areas far from human presence and obvious sources. Plastic debris also accumulates pollutants such as PCBs up to 100,000 to 1,000,000 times the levels found in seawater.
Plastics are increasingly used and much is wasted, deliberately or not, and end-up in the oceans: around 8 million tons a year of plastic bottles, bags, toys, six-pack rings, packaging bands and other plastic trash. Globally, plastic items (including microplastics) are the most abundant type of marine litter and the material the most often encountered by marine organisms. The physical effects of plastic debris due to both entanglement and ingestion have been clearly demonstrated. They injure and kill many marine life, including marine mammals.
Abandoned, lost or discarded fishing gears (ALDFG), such as nets and mono-filament lines, but also six-pack rings and strapping bands can cause entanglement. This causes injuries (laceration or cuts) and decreases swimming efficiency, and thereby efficiency in finding food and escaping predators. It can also cause death by drowning, suffocation or strangulation.
Over 50% of all marine mammal species have suffered from ingestion of marine debris or entanglement. Seals and sea lions are particularly affected, probably due to their very inquisitive nature. Of the large whales, the northern right whale and the humpback whale are the most affected by entanglement.
Plastic bags and packaging have become more resistant and plastic trash takes long time to degrade and disappear. The table below indicate how long things take for disappearing in the marine environment. Meanwhile they pose a serious threat to fish, seabirds and marine reptiles and mammals.
Biodegradation time in a marine environment (Mote Marine Laboratory 1993)
Plastic bags, in their 10-20 years of marine life, can be swallowed by many marine animals, either voluntarily – mismatched for food and prey, or involuntarily. The bags fill up or/and block the stomach, causing the animal to starve to death. Plastic bags can also cripple and entangle.
But the story does not stop there. Any dead animal will likely end-up as food for someone, and the plastic bag will continue filling another stomach or re-appear in the sea.