Global nutrient cycling by commercially targeted marine fish

Abstract. Throughout the course of their lives fish ingest food containing essential elements, including nitrogen (N), phosphorus (P), and iron (Fe). Some these elements are retained in body to build new biomass, which acts as a stored reservoir nutrients, while rest is excreted or egested, providing recycling flux water. Fishing activity has modified biomass distribution worldwide consequently may have altered fish-mediated nutrient cycling, but this possibility remains largely unassessed, mainly due difficulty estimating global metabolic rates. Here we quantify role commercially targeted marine between 10 g 100 kg (CTF10g100kg) cycling N, P, Fe ocean its change fishing activity, by using size-spectrum model populations calibrated observations catches. Our results show that amount nutrients potentially pristine CTF10g100kg generally small compared ambient surface concentrations might be significant nutrient-poor regions world: North Atlantic for oligotrophic gyres high-nutrient, low-chlorophyll (HNLC) Fe. Similarly, rate removal from through globally inputs can important locally, especially equatorial Pacific along western margin South America Africa. We also estimate was on order 3 % primary productivity demand globally, prior industrial fishing. The corresponding export egestion fecal matter 2.3 3.0 1 %–22 (Fe) total particulate more low-export tropical gyres. study supports significant, direct fraction ichthyosphere most notably Fe, been substantially Although were not able roles smaller species such mesopelagic because sparsity observational data, likely significantly trophic cascades, with impacts biogeochemical could comparable magnitude changes assess here.