Estimating Fishing Exploitation Rates to Simulate Global Catches and Biomass Changes of Pelagic and Demersal Fish

• Published in: Earth's future Vol. 12; no. 10
• Main Authors: Denderen, P. D., Jacobsen, N., Andersen, K. H., Blanchard, J. L., Novaglio, C., Stock, C. A., Petrik, C. M.
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.10.2024; Wiley
• Subjects: Biomass; Climate change; Climate effects; Climate models; demersal; Ecosystems; Estimates; Exploitation; Fish; fish guilds; Fisheries; Fishery policy; Fishing; marine ecosystem model; Marine ecosystems; Mortality; Ocean models; Oceans; pelagic; Predation; Simulation; Sustainable yield; Time series; trophic cascade
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2024EF004604

Robust projections of future trends in global fish biomass, production and catches are needed for informed fisheries policy in a changing climate. Trust in future projections, however, relies on establishing that models can accurately simulate past relationships between exploitation rates and ecosystem states. In addition, historical simulations are important to describe how the oceans have changed due to fishing. Here we use fisheries catch, catch‐only assessment models and effort data to estimate regional fishing exploitation levels, defined as the fishing mortality relative to fishing mortality at maximum sustainable yield (F/FMSY). These estimates are given for large pelagic, forage and demersal fish types across all large marine ecosystems and the high seas between 1961 and 2004; and with a ‘ramp‐up’ between 1841 and 1960. We find that global exploitation rates for large pelagic and demersal fish consistently exceed those for forage fish and peak in the late 1980s. We use the rates to globally simulate historical fishing patterns in a mechanistic fish community model. The modeled catch aligns with the reconstructed catch, both for total catch and catch distribution by functional type. Simulations show a clear deviation from an unfished model state, with a 25% reduction in biomass in large pelagic and demersal fish in shelf regions in recent years and a 50% increase in forage fish, primarily due to reduced predation. The simulations can set a baseline for assessing the effect of climate change relative to fishing. The results highlight the influential role of fishing as a primary driver of global fish community dynamics. Plain Language Summary Fishing can heavily impact the number and types of fish in a region. Yet, simulating the historical impacts of fishing on fish communities is challenging, especially on a global scale. This is because for many places, we do not know how many fish are in the sea and what fraction of these fish die from fishing each year. In this study, we estimated the historical rate by which fisheries have caught fish globally. We used these data in a mathematical model to simulate the number of fish in the sea; both with and without fishing. The model shows that fishing has reduced the biomass of big predators (large pelagic and demersal fish) by 25% in shelf regions. This decline led to less predation on forage fish and a 50% increase in forage fish biomass, despite fishing of forage fish. These simulations will allow estimating the relative effects of climate change and fishing on current and future fish communities. Key Points We estimated global gridded fishing exploitation patterns for large pelagic, forage and demersal fish types using catch and effort data Food‐web simulations with reconstructed fishing exploitation rates broadly replicated catch trends of diverse ecosystems on a global scale Global biomass declines due to fishing of large pelagic and demersal fish leads to increases in forage fish via a trophic cascade