Summary

  • 1 kg of plastic is emitted to the ocean per capita per year[1].
  • 0.0002 seabirds / marine 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 1 M times as large as the number of seabirds / marine mammals killed by marine plastic pollution.

The data and calculations are presented below.

Data

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 or marine mammal (PEOpD): < PEO / (DS + DMM) = 8 Mt / (1 M + 100 k) = 7.27 t.
  • Seabirds / Marine mammals killed by per capita plastic marine pollution in 2010 (DpC): > PEOpC / PEOpD = 1.16 / 7.27 k = 159 u.
  • 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 / marine mammals killed by marine plastic pollution: WFpC / DpC = 234 / 159 u = 1 M.
  1. ^

    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.

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

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.

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!