Bottom-up drivers of global patterns of demersal, forage, and pelagic fishes

• Published in: Progress in oceanography 2019-09, Vol.176, p.102124, Article 102124
• Main Authors: Petrik, Colleen M., Stock, Charles A., Andersen, Ken H., van Denderen, P. Daniël, Watson, James R.
• Format: Article
• Language: English
• Subjects: Allometry; Ecosystem; Fisheries oceanography; Mechanistic model; Trophodynamics
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2019.102124

•Global, spatially explicit, mechanistic model of forage, pelagic, and demersal fish.•Includes life cycle transitions, trophic interactions, and allometry of rates.•Captures cross-ecosystem differences in fish assemblages and productivity.•Dominance of large pelagics vs. demersals linked to the zooplankton to benthos ratio.•Can be coupled to earth system models for climate change projections. Large-scale spatial heterogeneity in fisheries production is predominantly controlled by the availability of zooplankton and benthic organisms, which have a complex relationship with primary production. To investigate how cross-ecosystem differences in these drivers determine fish assemblages and productivity, we constructed a spatially explicit mechanistic model of three fish functional types: forage, large pelagic, and demersal fishes. The model is based on allometric scaling principles, includes basic life cycle transitions, and has trophic interactions between the fishes and with their pelagic and benthic food resources. The model was applied to the global ocean, with plankton food web estimates and ocean conditions from a high-resolution earth system model. Further, a simple representation of fishing was included, and led to moderate matches with total, large pelagic, and demersal catches, including re-creation of observed variations in fish catch spanning two orders of magnitude. Our results highlight several ecologically meaningful model sensitivities. First, coexistence between forage and large pelagic fish in productive regions occurred when forage fish survival is promoted via both favorable metabolic allometry and enhanced predator avoidance in adult forage fish. Second, the prominence of demersal fish is highly sensitive to the efficiency of energy transfer to benthic invertebrates. Third, the latitudinal distribution of the total catch is modulated by the temperature dependence of metabolic rates, with increased sensitivity pushing fish biomass toward the poles. Fourth, forage fish biomass is suppressed by strong top-down controls on temperate and subpolar shelves, where mixed assemblages of large pelagic and demersal fishes exerted high predation rates. Last, spatial differences in the dominance of large pelagics vs. demersals is strongly related to the ratio of pelagic zooplankton production to benthic production. We discuss the potential linkages between model misfits and unresolved processes including movement, spawning phenology, seabird and marine m