The number of seabirds and sea mammals killed by marine plastic pollution is quite small relative to the catch of fish

Vasco Grilo

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 M t (PEO) according to OWID.
The world population in 2010 was 6.92 G (WP) according to The World Bank.
Marine plastic debris kills up to 1 M seabirds (SB) and 100 k sea mammals (SM) each year according to the United Nations.
The catch of wild fish is 0.97 T/year (WFL) to 2.7 T/year (WFH) according to fishcount.org.

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 per capita plastic marine pollution in 2010 (DSBpC): PEOpC / PEOpDSB = 1.16 / 8 k = 145 μ.
Sea mammals killed by per capita plastic marine pollution in 2010 (DSMpC): PEOpC / PEOpDSM = 1.16 / 80 k = 14.5 μ.
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.

^{^}
1 kg is the global value, and it is much smaller for many countries. Most of the countries emit less than 0.1 % of the plastic waste to the ocean (see this map), although 3 % of the global plastic waste is emitted to the ocean.

Forecasting & estimation1Cause prioritization1Animal welfare1Wild animal welfare4Fermi estimate2

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[-]MichaelStJules1y110

Do you have any thoughts on the effects of plastic pollution on wild fish?

[-]Vasco Grilo1y50

According to this section from OWID:

"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".
"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.

[-]Raluca Laslo2mo40

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?

[-]Lorenzo Buonanno2mo40

kg is kilograms, t is tonnes, but what is u and what is M?

They are SI Prefixes: M stands for mega or 1 million, 10^6.
u (for μ) stands for micro or 1 millionth, 10 ^ -6.

Is the conclusion that catching wild fish does more damage to the ecosystem than throwing plastic into the ocean

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.

[-]Vasco Grilo2mo40

Thanks for noting that, Raluca! Thanks for clarifying, Lorenzo!

I have now added links to the 1st instances of each of the prefixes.

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.

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.

[-]LMKull5mo40

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.

[-]saline_A2mo20

very true

[-]Rory Fenton1y40

I really appreciated this short, clear post. Thank you!

[-]AndreFerretti1y30

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."

[-]Vasco Grilo1y60

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.

[-]AndreFerretti1y101

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

[-]Vasco Grilo1y20

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).

[-]Marshal1y20

Thanks for sharing this!