From siphonophores to deep scattering layers: uncertainty ranges for the estimation of global mesopelagic fish biomass

Roland Proud, Nils Olav Handegard, Rudy Kloser, Martin Cox, Andrew Stuart Brierley

Research output: Contribution to journalArticlepeer-review

58 Citations (Scopus)

Abstract

The mesopelagic community is important for downward oceanic carbon transportation and is a potential food source for humans. Estimates of global mesopelagic fish biomass vary substantially (between 1 and 20 Gt). Here, we develop a global mesopelagic fish biomass model using daytime 38 kHz acoustic backscatter from deep scattering layers. Model backscatter arises predominantly from fish and siphonophores but the relative proportions of siphonophores and fish, and several of the parameters in the model, are uncertain. We use simulations to estimate biomass and the variance of biomass determined across three different scenarios; S1, where all fish have gas-filled swimbladders, and S2 and S3, where a proportion of fish do not. Our estimates of biomass ranged from 1.8 to 16 Gt (25–75% quartile ranges), and median values of S1 to S3 were 3.8, 4.6, and 8.3 Gt, respectively. A sensitivity analysis shows that for any given quantity of fish backscatter, the fish swimbladder volume, its size distribution and its aspect ratio are the parameters that cause most variation (i.e. lead to greatest uncertainty) in the biomass estimate. Determination of these parameters should be prioritized in future studies, as should determining the proportion of backscatter due to siphonophores.
Original languageEnglish
Pages (from-to)718-733
JournalICES Journal of Marine Science
Volume76
Issue number3
Early online date19 Apr 2018
DOIs
Publication statusPublished - May 2019

Keywords

  • Myctophids
  • DSLs
  • Acoustics
  • Swimbladder
  • Pneumatophore
  • Scattering models
  • Resonance

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