How many fish are in the sea?
June 27, 2021 8:33 PM   Subscribe

Are there any good counts of mesopelagic fish biomass by species or family?

I was reading about the deep scattering layer caused by lanternfish, and came across the following: "Sampling via deep trawling indicates that lanternfish account for as much as 65% of all deep sea fish biomass. Indeed, lanternfish are among the most widely distributed, populous, and diverse of all vertebrates."

This seems to contradict this info about another mesopelagic fish, the bristlemouth: "bristlemouths make up for their lack of diversity with numbers: Cyclothone, with 13 species, is thought to be (along with Vinciguerria) the most abundant vertebrate genus in the world, numbering in the hundreds of trillions to quadrillions."

Are there any counts of estimated mesopelagic fish biomass that reconcile these two statements? Or am I comparing apples and oranges - there are more Cyclothone bristlemouths than any other genus, but overall more fish of the Myctophidae (lanternfish) family? Or do we just not have a good census of global fish biomass by which to make this comparison?
posted by Paragon to Science & Nature (4 answers total)
You are comparing number to biomass--both can be true if bristlemouth are much smaller.
posted by agentofselection at 10:46 PM on June 27, 2021

Response by poster: Yeah, that's a completely logical read on the quotes above, thank you. But as far as I can tell lanternfish and bristlemouths are roughly the same size (no more than 30cm long, less depending on the species etc.), so my confusion remains.
posted by Paragon at 2:54 AM on June 28, 2021

Lanternfish belongs to a family, the specific bristlemouths to a genus. So cyclothone, one genus, can be the most abundant single genus, while lanternfish, which have a large number of genuses in the family, can compose more of the overall biomass as long as no one genus has more fish than cyclothone.
posted by tchemgrrl at 6:14 AM on June 28, 2021

The podcast Unexplainable did an episode about the mesopelagic layer, "The Twilight Zone of the Ocean" (transcript) not too long ago. Relevant to this question, a 2014 study found there were perhaps 10 times as many fish in the mesopelagic as were previously thought. The podcast emphasizes that even that is a very rough estimate, and there's still a lot that's unknown about the mesopelagic.

In the two Wikipedia articles you link, the lanternfish claim is cited to a 1998 work, and the bristlemouth claim to a 2015 NYT article, so it may just reflect a change in our understanding of mesopelagic life between 1998 and 2015.
posted by DevilsAdvocate at 8:17 AM on June 28, 2021 [3 favorites]

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