The number of seabirds and sea mammals killed by marine plastic pollution is quite small relative to the catch of fish
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.
Do you have any thoughts on the effects of plastic pollution on wild fish?
According to this section from Our World in Data:
“Microplastic ingestion rarely causes mortality in any organisms. As such, ‘lethal concentration’ (LC) values which are often measured and reported for contaminants do not exist”. Update on 29 December 2023: Nathalie Gil pointed out some studies have concluded microplastics increase mortality.
“There is increasing evidence that microplastic ingestion can affect the consumption of prey, leading to energy depletion, inhibited growth and fertility impacts”.
“Evidence of impacts of reduced food consumption include” (the links below were also taken from the OWID article):
“Slower metabolic rate and survival in Asian green mussels” (see this).
“Reduced reproducibility and survival in copepods” (see this).
“Reduced growth and development of Daphnia” (see this).
“Reduced growth and development of langoustine” (see this).
“Reduced energy stores in shore crabs and lugworms” (see this and this).
However, it is worth noting that reduced food consumption tends to decrease the size of the fish population, which might be beneficial if fish have net negative lives.
Sorry, but I don’t understand the meaning of this article because I am having trouble understanding the measurements. kg is kilograms, t is tonnes, but what is u and what is M? Also, is the conclusion that catching wild fish does more damage to the ecosystem than throwing plastic into the ocean? How should I interpret the sentences?
They are SI Prefixes: M stands for mega or 1 million, 10^6.
u (for μ) stands for micro or 1 millionth, 10 ^ −6.
If I understand correctly, the conclusion is that the direct effects of marine plastic pollution on seabirds / marine mammals are probably much smaller than the effects of fishing on fish.
Thanks for noting that, Raluca! Thanks for clarifying, Lorenzo!
I have now added links to the 1st instances of each of the prefixes.
Yes, I think this is exactly the right conclusion to take. We should be careful not to extrapolate to other animals. I have now updated the title to better reflect this.
Thanks for adding those links, definitely helpful.
I think it might be more comprehensible to use 10^x notation, given I imagine most readers would be more familiar with that concept (happy to be corrected). It would also make it so units would be comparable (i.e., it’s easy to see that 10^-8 is much less than 10^-4) without switching back and forth between a Wikipedia article (as I had to do).
Thanks for the suggestion, Mitchell, and welcome to the EA Forum!
Now I use words to introduce the data, and only afterwards provide the prefixes in parentheses:
In the calculations, I also clarify what is the meaning of the prefix I introduce there:
I agree with you that 10^x notation is more well known, so you do have a point! On the other hand, I wonder whether using prefixes could be useful for people to get familiar with more notations.
Proposed corrections to some possible typing errors:
Original text: “Seabirds killed by per capita plastic marine pollution in 2010”
Proposed edit: “Seabirds killed by plastic marine pollution in 2010, per capita”
Similarly:
Original text: “Sea mammals killed by per capita plastic marine pollution in 2010”
Proposed edit: “Sea mammals killed by plastic marine pollution in 2010, per capita”
Discussion:
It’s birds-killed-per-capita, not pollution-per-capita.
Thanks! Corrected.
First of all, I am very sorry if this was cited on the comments before, I did not have time to read all of it. I’d like to share some views on this: I completely agree that fishing is way more impactful for the ocean than plastic nowadays! However, it is not in the same proportion it’s been shared here in this logic above. The main reason why is that it only calculates the death of birds and marine mammals killed by plastic x fish caught by the fishing industry. They left fish (also other animals such as corals, cephalopods, turtles, etc.) that die from plastic aside on the measurement of deaths by plastic per year, and used fish and other comercialised marine life (a group of species much more abundant in termos of biomass than birds and seabirds) to calculate impact of fishing. There is no data on sea mammals or birds on fishing impact , no data of fish for plastic impact. It is apples compared to oranges, this calculation has a huge flaw! If we want to compare ‘like for like’ (knowing there is no study on the impact of plastic on the death of fishes yet done, due to the low conservationists’ interest in this), I then bring a comparison of deaths of sea mammals and sea birds from plastic pollution x fishing (as they also die in hoards because of bycatch!). There is the study that says that 300,000 mammals and that 320,000 seabirds are killed per year by fishing alone. This brings a much more comparative number, and it does show that plastic certainly impacts in a similar way or more (as per your numbers above, it kills around 1,000,000 birds/ 100,000 marine mammals). So yeah, as this more just comparison indicates: fighting plastic, as well as fighting commercial fishing, is ESSENTIAL to protect marine lives.
Let me know our thoughts on this. Best,
Nathalie Gil
President of Sea Shepherd Brazil
Hi Nathalie,
Thanks for the comment, and welcome to the EA Forum!
I agree plastic pollution may affect many more animals besides the seabirds and sea mammals I included in the calculation. Michael St. Jules also asked about the effects on wild fish, and I shared some related information. You may want to check Brian Tomasik’s posts on fishing too.
I am confused by this part. If fishing is responsible for even more deaths of other animals, then the conclusion of the post that fishing may be causing many more deaths than plastic pollution is reinforced, right?
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.
Thanks for the comprehensive reply! Strongly upvoted.
The statement you quote refers to microplastic ingestion, but the study you link does not contain “microplastic”, so it may be focussing just on larger pieces of plastic:
However, based on the other studies you linked, I agree the statement “microplastic ingestion rarely causes mortality in any organism” was misleading. I was quoting a page from Our World in Data which has meanwhile been modified, and no longer seems to discuss impacts on wildlife. However, they now have a FAQ on microplastics which reflects uncertainty about the effects on mortality, rather than confidence in the absence of effects (emphasis mine):
I have added to the comment replying to Michael the following. “Update on 29 December 2023: Nathalie Gil pointed out some studies have concluded microplastics increase mortality”.
Nitpick, microplastics have a diameter of less than 5 mm (which makes your point even more valid).
Besides often having numbers, another common thread of Brian’s posts is that the impact of reducing fishing may be quite unclear due to indirect effects. To illustrate, here is the summary of How Wild-Caught Fishing Affects Wild-Animal Suffering:
I guess wild animals have net positive lives, although it is quite unclear, so I think we had better minimise fishing and plastic pollution.
Makes sense! I have added the following at the top of the post. “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”.
Thanks for your reply, Vasco—all clear and comprehensive. I’d only dispute the claim from How Wild-Caught Fishing Affects Wild-Animal Suffering: ‘for example, catching big piscivorous fish may reduce zooplankton populations, while catching small zooplanktivorous fish may increase zooplankton populations.’ - this does not consider the full balance of the trophic chain, and the fact that if you remove big piscivorous fish, you are in fact on the SHORT TERM increasing the population of zooplankton, however, this have many complex effects, one example: the decrease in the Caribbean shark population is met by an increase in its prey, the grouper fish. The expanding grouper population takes parrotfish, normally responsible for clearing coral of algae, in greater numbers. This could explain why algae now dominates many degraded reefs in the Caribbean. It also shows how the systematic elimination of one species—a key link in a complex web of relationships—can destabilize the entire ecosystem. When it comes to wild animals, no impact is so straightforward and isolated as we’d like to measure. This is my pet critic with EA, as the difficulty in measuring the clean direct impact of efforts in wildlife conservation can be hindering funds to these efforts, however, in the larger sense, the strategy to leave the ocean alone to rebalance its ecosystems is about saving all life on Earth—therefore the investment on ocean conservation has strong direct links to Existential Risk—ours and of all life on Earth. Perhaps this is a conversation to another topic/ thread...!!
I think it is crucial to point out that while there may be little direct effect of plastic pollution on morality of animals, plastic (mainly microplastic) is a vessel for pollutants and can therefore transport in chemicals, which can cause death in the organism. Therefore the effect of plastic is indirect, while clearly still playing a very crucial role.
very true
I really appreciated this short, clear post. Thank you!
Thanks for the post. I learnt about the size of the plastic pollution problem for animals.
I can’t entirely agree with the framing of the article. 1M seabirds dying per year from plastic is not “small”. It makes me think that this is not a big problem, and I shouldn’t worry at all about it.
I would frame it as “1M seabirds die every year from plastic pollution, so it’s a big problem (malaria kills 0.5M people per year), but it’s still 1 million times less than 1T fish slaughtered per year.”
Great to know that you found it useful!
In my mind, the meaning of words such as “small” and “large” is always context-dependent. In this case, I think it is fair to say that the impact, measured as the number of deaths, from marine plastic pollution on seabirds and marine animals is small in comparison with the impact of catching fish.
In order to make comparisons between species, I think it is worth having in mind the number of neurons (a proxy for sentience) respecting each death toll.
Estimates for the number of neurons:
Humans: 86 G (see this).
Marine mammals: 7.10 G.
Geometric mean of the neurons for “Harp seal” and “Killer whale”, which are the species in this list with the least and most neurons that are marine mammals.
Seabirds: 606 M.
Geometric mean of the neurons for “Mallard” and “Mute swan”, which are the animals in this list with the least and most neurons that look somewhat similar to seabirds.
Fish: 10 M (see “Adult zebrafish” in this list).
Number of neurons respecting each death toll:
Malaria: 627 k * 86 G = 53.9 P.
Marine mammals: 100 k * 7.10 G = 0.710 P.
Seabirds: 1 M * 606 M = 0.606 P.
Fish: 1.62 T * 10 M = 16.2 kP.
Consequently, the number of neurons regarding:
Marine mammals and seabirds is similar.
Malaria is ~ 2 orders of magnitude larger than that of marine mammals / seabirds.
Fish is ~ 2.5 orders of magnitude larger than that of malaria.
From the above, it naively seems that:
The death toll of marine mammals / seabirds caused by marine plastic pollution is small relative to the death toll caused by malaria.
The death toll caused by malaria is small relative to the death toll concerning wild fish catch.
However, this is not by all means a definite analysis:
It is unclear whether sentience should be measured as a linear function of the number of neurons (see section “Brain size” of this page).
Even for the same level of sentience, the intensity of the death could vary.
There are other effects which are not captured by the number of deaths.
I didn’t know fish had 10M neurons. Thanks!
I appreciate your quantitative thinking. But I believe it’s unfair to say that a fish is 10,000X worth less than a human because a fish has fewer neurons. What if suffering has a minimum threshold of neurons and then declining marginal suffering after that? We don’t know (as you point out in your last paragraph).
“Not everything that can be counted counts and not everything that counts can be counted.”
—Einstein
Yes, I agree, there is lots of uncertainty! Moreover:
In addition to the importance of the death toll, one has to take into account its neglectedness and tractability.
Longterm effects should also be assessed, as they can concern most the expected impact of averting deaths (e.g. via expansion of the moral circle).
Thanks for sharing this!