Disclaimer: plastic pollution may well kill way more animals besides seabirds and sea mammals. There are 6.20*10^14 wild fish and 1.00*10^20 wild marine arthropods, but only 6.75*10^11 wild mammals.
Summary
- 1 kg of plastic is emitted to the ocean per capita per year[1].
- 0.0001 seabirds and 0.00001 sea mammals are killed by marine plastic pollution per capita per year.
- 200 wild fish are caught per capita per year.
- The catch of wild fish is 2 M times as large as the number of seabirds, and 20 M times as large as the number of sea mammals killed by marine plastic pollution.
The data and calculations are presented below.
Data
- The plastic emitted to the ocean in 2010 was 8 million tonnes according to OWID (PEO = 8 Mt).
- The world population in 2010 was 6.92 billion according to The World Bank (WP = 6.92 G).
- Marine plastic debris kills up to 1 million seabirds and 100 thounsand sea mammals each year according to the United Nations (SB = 1 M, and SM = 100 k).
- The catch of wild fish is 0.97 to 2.7 trillion/year according to fishcount.org (WFL = 0.97 T/year to WFH = 2.7 T/year).
Calculations
- Plastic emitted to the ocean per capita in 2010 (PEOpC): PEO / WP = 8 Gkg / (6.92 G) = 1.16 kg.
- Plastic emitted to the ocean to cause one death of a seabird (PEOpDSB): PEO / SB = 8 Mt / (1 M) = 8 t.
- Plastic emitted to the ocean to cause one death of a sea mammal (PEOpDSM): PEO / SM = 8 Mt / (0.1 M) = 80 t.
- Seabirds killed by plastic marine pollution in 2010, per capita (DSBpC): PEOpC / PEOpDSB = 1.16 / (8 k) = 145 μ (145 seabirds killed per million people).
- Sea mammals killed by plastic marine pollution in 2010, per capita (DSMpC): PEOpC / PEOpDSM = 1.16 / (80 k) = 14.5 μ (14.5 sea mammals killed per million people).
- Wild fish caught per year (WF): (WFL * WFH)^0.5 = (0.97 * 2.7)^0.5 T = 1.62 T.
- Catch of wild fish per capita per year (WFpC): WF / WP = 1.62 T / (6.92 G) = 234.
- Ratio between the catch of wild fish and the number of seabirds killed by marine plastic pollution: WFpC / DSBpC = 234 / (145 μ) = 1.62 M.
- Ratio between the catch of wild fish and the number of sea mammals killed by marine plastic pollution: WFpC / DSMpC = 234 / (14.5 μ) = 16.2 M.
This work is licensed under a Creative Commons Attribution 4.0 International License.
Hello Vasco, thank you a lot for your reply. Some food for thought (as I did not extend a full analysis of all being mentioned and shared):
First, I'll respond to your second comment. As you can see in the numbers, fishing is responsible for more seabird deaths, but less death of mammals. But what I wanted to point out is that this is a more comparable number (and shows a group of animal can indeed suffer more by plastic than fishing or vice-versa) and it only reveals a part of the numbers, as I stated too in my response. As I said from the start: fishing is the single most cause of death in the ocean, if you include all fish, crustacea (if krills are included the numbers, the numbers of lives can be estimated to the quatrillions, as we fish 2.7 million tons of krill per year, and a krill's weight is 1 gram per average), though we shan't ignore the huge impact of plastic in the ocean, as the numbers shown can give higher impact to some of the groups of animals versus others.
Secondly, I read your reply from Michael St Jules, though affirming that 'microplastic ingestion rarely causes mortality in any organism' can't be farther from the truth. As an example from what we already debated, this is what led to the seabird numbers (as there are dozens of studies proving that plastic debris is their cause of death, as you had also pointed out). An example of study here: https://www.nature.com/articles/s41598-018-36585-9 .
For fish, the influence of plastic and microplastic causing deaths can be seen in some rare studies, some here:
An interesting study with Rainbow Trouts, is that when fish is exposed to MP and a virus, the chances of dying from the virus goes from 20% than up to 80%! Study here: https://www.sciencedirect.com/science/article/abs/pii/S004896972208295X?via%3Dihub
https://iopscience.iop.org/article/10.1088/1755-1315/631/1/012006/pdf#:~:text=The%20microplastics%20can%20have%20a,oxidative%20damage%20and%20abnormal%20behavior. - This brings an analysis of the plankton Daphinia magna you also shared a study from, showing the death effects of a 0,001 millimetre of plastic (microplastics are debris of 0,5mm or less, so this fits the size with a lot to spare) on their death rate (page 5).
Important to note that these types of research pose a difficulty, as death because of microplastic ingestion takes a while to study and is not realistic to be done in labs/ aquaria. There are more studies on marine mammals, turtles and seabirds in their natural habitat as these are examined more commonly by WW environmental agencies when reaching the surface/ ashore (and thus the numbers can be better extrapolated) than fish, frankly revealing the massive speciesism in the marine biology/ environmental studies arena. Also, important to note that these studies we both brought above focus on microplastic, and not cover the ingestion of larger plastic litter by fish, which we know can be the cause of deaths by entanglement, filled stomach (starvation) and choking. In short, there is a clear lack of study on fish deaths by consumption of plastic debris in general.
Another fact to point out on the fishing x plastics debate is that if we immediately stop fishing, the alleviation of the impact on marine life will be immediate, and complete. If we stop using plastics today, we would still have to manage the millions of tons of plastic we had already produced, and that are still in the environment. A study shows that if we stop using virgin plastic right now, in 2050 the amount of microplastics in the ocean will more than double by 2050, coming from the existing plastic pollution: https://www.researchgate.net/publication/358446217_Impacts_of_plastic_pollution_in_the_oceans_on_marine_species_biodiversity_and_ecosystems
I am roughly aware of Brian Tomasik's numbers on fishing as I work to fight against it myself.
Just to be dead clear, I still am in complete alignment with you regarding the impact of fishing x plastics for the ocean's ecosystem, as a fighter for the end of fishing myself. I just wanted to shed a light on why not to de-prioritise the efforts on fighting plastic pollution for the protection of the ocean.
Thanks for sharing and for the debate.