Abstract
AbstractThe 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.
Highlights
IntroductionThe mesopelagic community plays an important role in global biogeochemical cycling and the biological carbon pump, and is attracting increasing attention from commercial fishers (St John et al, 2016)
In this article, we consider, from the standpoint of available acoustic survey data, what the global biomass of mesopelagic fish might be.The importance of the mesopelagic communityThe mesopelagic community plays an important role in global biogeochemical cycling and the biological carbon pump, and is attracting increasing attention from commercial fishers (St John et al, 2016)
Our method was as follows: (i) define a generalized acoustic biomass model, (ii) obtain a global mean value of mesopelagic backscatter from the literature (Proud et al, 2017), (iii) with reference to acoustic scattering models, review the dominant sources of backscatter found within the mesopelagic zone, (iv) define mesopelagic fish biomass model and identify unknown parameters and possible confounding animal behaviours, (v) define plausible statistical distributions to capture the full range of uncertainty in the unknown parameters and develop scenarios to simulate a range of animal behaviours, (vi) quantify uncertainty across all scenarios where g is the group index, m is the group member index and rbsg;m (m2) is the backscattering cross-section for member m of group g
Summary
The mesopelagic community plays an important role in global biogeochemical cycling and the biological carbon pump, and is attracting increasing attention from commercial fishers (St John et al, 2016). Biogeochemical and ecosystem models which simulate the biological carbon pump require validation of the mesopelagic component to provide confidence in their predictions of vertical carbon flux, which itself feeds into climate/Earth-system models (Giering et al, 2014). A substantial amount of mesopelagic biomass in the 1 mmþ size fraction is contained, during the day, within deep scattering layers (DSLs), primarily made up of fish, zooplankton, squid, and jellyfish.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
