Preprints
https://doi.org/10.5194/bg-2021-251
https://doi.org/10.5194/bg-2021-251

  27 Sep 2021

27 Sep 2021

Review status: this preprint is currently under review for the journal BG.

Global nutrient cycling by commercially-targeted marine fish

Priscilla Le Mézo1,2, Jérôme Guiet3, Kim Scherrer1, Daniele Bianchi3, and Eric Galbraith1,4,5 Priscilla Le Mézo et al.
  • 1Institut de Ciencia i Technologia Ambientals (ICTA), Universitat Autonoma de Barcelona (UAB), Barcelona, Spain
  • 2Laboratoire de Météorologie Dynamique, ENS Ulm, Paris, France
  • 3Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, United States
  • 4Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, Spain
  • 5Earth and Planetary Sciences, McGill University, Montreal, QC, Canada

Abstract. Throughout the course of their lives fish ingest food containing essential elements, including nitrogen (N), phosphorus (P) and iron (Fe). Some of these elements are retained in the fish body to build new biomass, which acts as a stored reservoir of nutrients, while the rest is excreted or egested, providing a recycling flux to water. Fishing activity has modified the fish biomass distribution worldwide and consequently may have altered fish-mediated nutrient cycling, but this possibility remains largely unassessed, mainly due to the difficulty of estimating global fish biomass and metabolic rates. Here we quantify the role of commercially-targeted marine fish between 10 g and 100 kg () in the cycling of N, P and Fe in the global ocean, and its change due to fishing activity, by using a global size-spectrum model of marine fish populations calibrated to observations of fish catches. Our results show that the amount of nutrients stored in the global pristine , biomass was generally small compared to the ambient surface nutrient concentrations but significant in the nutrient-poor regions of the world: the North Atlantic for P, the oligotrophic gyres for N and the High Nutrient Low Chlorophyll (HNLC) regions for Fe. Similarly, the rate of nutrient removed from the ocean through fishing is globally small compared to the inputs, but can be important locally especially for Fe in the equatorial Pacific and along the western margin of South America and Africa. This model allowed us to compute the spatial distribution of the cycling of elements by the biomass at pristine and global peak catch state, which is relatively small compared to the estimated primary production demand for nutrients and estimated export production of nutrients. Pristine cycling (excretion + egestion) accounted for less than 2.7 % of the primary productivity demand for N, P and Fe globally. Relative to the export of nutrients, modeled global pristine egestion represents on average 2.3 %, 3.0 % and 1.1–22 % for N, P and Fe (low-high estimates), respectively, with a higher fraction in the low-export oligotrophic tropical gyres. Our study highlights the role of the fraction of the icthyosphere (i.e. does not include non-commercial species such as mesopelagic fish) on nutrient storage and cycling, and the potential role of fishing activities on this cycling, which could be of importance in regions of low nutrient concentration, high fish biomass and/or high productivity demand, and especially at the more local scale for Fe.

Priscilla Le Mézo et al.

Status: open (until 08 Nov 2021)

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Priscilla Le Mézo et al.

Priscilla Le Mézo et al.

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Short summary
This study analyses if the amount of nutrients in the fish biomass is significant compared to the nutrients available in the water column and also if the cycling rates of nutrients by the fish biomass is significant compared to how much nutrients primary producers need to grow. The use of a global model of commercially-targeted fish biomass allow us to assess these contributions of fish at the global scale, in a pristine ocean as well at the time of the global peak catch.
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